MX2007006110A - Plants having increased yield and a method for making the same - Google Patents

Abstract

The present invention concerns a method for increasing plant yield by increasing activity in a plant of an OsMADS18-like polypeptide or a homologue thereof. One such method comprises introducing into a plant an OsMADS18-like nucleic acid or variant thereof. The invention also relates to transgenic plants having introduced therein an OsMADS18-like nucleic acid or variant thereof, which plants have increased yield relative to corresponding wild type plants. The present invention also concerns constructs useful in the methods of the invention.

Description

PLANTS WHICH HAVE INCREASED PERFORMANCE AND A METHOD FOR PREPARING THE SAME FIELD OF THE INVENTION The present invention relates generally to the field of molecular biology and has to do with a method to increase the yield of plants in relation to the corresponding wild plants. . More specifically, the present invention relates to a method for increasing the yield of plants, increasing the activity in a plant of a polypeptide similar to Oryza sativa (Os) MADS18 or a homologue thereof. The present invention also relates to plants having increased activity of a polypeptide similar to OsMADS18 or a homologue thereof, which plants have an improved yield relative to the corresponding wild plants. The invention also provides constructs useful in the methods of the invention. BACKGROUND OF THE INVENTION The growing world population and the increasingly smaller reserve of arable land, available for agricultural food research to improve the efficiency of agriculture. Conventional means for growing and horticultural improvements use selective breeding techniques to identify plants that have desirable characteristics. However, such selective breeding techniques have several disadvantages, that is, these techniques are typically labor-intensive and result in plants that frequently contain heterogeneous genetic components, which may not always result in the desirable characteristic that is transmitted from the original plants. Advances in molecular biology have allowed man to modify the germplasm of animals and plants. Plant genetic engineering involves the isolation and manipulation of genetic material (typically in the form of DNA or RNA) and the subsequent introduction of genetic material into a plant. Such technology has the capacity to supply crops or plants that have several economic, agronomic or horticultural characteristics, improved. A characteristic of particular economic interest is performance. Yield is usually defined as the measurable product of economic value of a crop. This can be defined in terms of quantity and / or quality. The performance depends directly on several factors, for example, the number and size of the organs, the architecture of the plant (for example, the number of branches), seed yield and more. Root development, nutrient absorption and tolerance to extreme conditions can also be important factors in determining yield. Therefore optimization of one of the aforementioned factors can increase crop yield. The ability to increase plant yield could have many applications in areas such as agriculture, including the performance of ornamental plants, arboriculture, horticulture and forestry. It has now been found that the increased activity in a plant of a polypeptide similar to 0sMADS18 gives plants that have an increased yield relative to the corresponding wild plants. The MADS-box genes (MCM1 in yeast, Agamous and Deficiens in plants, and SRF (serum response factor) in humans) constitute a large family of genes of transcriptional, eukaryotic regulators, involved in various aspects of the development of yeasts, plants And animals. The MADS-box genes encode a strongly conserved MADS domain, responsible for the binding of DNA to specific boxes in the regulatory region of their target genes. The gene family can be divided into two main lineages, type I and type II. Type II genes are also called MIKC type proteins, they refer to the four functional domains they possess (see Figure 1, from Jack (2001) Plant Molec Biol 46: 515-520): -MADS for the link of DNA, approximately 60 amino acids (highly conserved) located at the N-terminal end of the protein; -I for the intervention domain (less conserved), involved in the selective training of the MADS dimer; -K for the keratin domain (well conserved) responsible for the dimerization; -C for the C-terminal region (variable in sequence and length) involved in the transcriptional activation, or in the formation of a multimeric complex of transcription factor. More than 100 MADS-box genes have been identified in the Arabidopsis, and have been phylogenetically classified in 12 ciados (group of organisms that are defined by exclusive characters to all their members and that distinguish the group from all the others), each one has specific derivations of the MADS consensus (Thiessen et al. (1996) J Mol Evol 43: 44-516). The OsMADS18 (formerly called FDRMADS7 or OsMADS28) belongs to the SQUA (for SQUAMOSA, of Antirrhinum majus), together with the following genes of the Arabidopsis: FUL / Agl8 (FRUITFULL), CAL / AgllO (CAULIFLOWER), APl / Agl7 (APETALA1 ) and the less characterized MADS AGL79. The genes of the CED SQUA are identification genes of organs of function A with reference to the identification model of floral organs ABC as proposed by Coen and Meyerowitz in 1991 (Nature 353: 31-7). Rice has four genes from group A: 0sMADS14, 0sMADS15, 0sMADS18, and OsMADS20, each being a member of the SQUA group. The CATA SQUA in the dicotyledons is subdivided into two subgroups, the API and FUL subclades. These subclades diverge essentially with respect to specific amino acid motifs or portions, located at the C-terminal end of their respective proteins (Litt and Irish (2003) Genetics 165: 821-833). In addition to the presence of a specific API amino acid motif, the related proteins of the dicot API, usually comprise a farnesylation motif or radical at its C-terminus (this motif is CAAX, where C is cysteine, A is usually a aliphatic amino acid, and X is methionine, glutamine, serine, cysteine or alanine). In monocotyledons, the proteins of the SQUA protein are also subdivided into two main groups, which can be distinguished based on the C-terminal motifs, located within the last 15 amino acids of the proteins: LPP MLRT (SEQ ID NO: 18 ) and LPP MLSH (SEQ ID NO: 19) (Figure 2). In contrast to the dicotyledonous sequences of the SQUA, monocot sequences of the SQUA ciate, it does not possess a farnesylation motif at its C-terminal end.

The ADS18 Os is pooled with the ZMM28 polypeptide from corn and the m3 polypeptide from barley (Becker and Thiessen (2003) Moli Phylogenet Evol 29 (3): 464-89). All three proteins comprise the amino acid motif LPP MLRT within approximately 15 amino acids of its C-terminal end. The other two MADS box proteins from the SQUA rice, OsMADS14 and OsMADS15, belong to the subclass with the motif LPPWWMLSH within approximately the last 15 amino acids of its C-terminal end. For both of these motifs, LPPWMLRT (SEQ ID NO: 18) and LPPWMLSH (SEQ ID NO: 19), the most conserved amino acids are located in the second (P for proline) and fourth (W for tryptophan) positions. OsMADS18 is a widely expressed gene and its RNA can be detected in roots, leaves, fluorescence and tissue of growing seeds (Masiero et al (2002) J Biol Chem 277 (29): 26429-35). The OsMADS18 can be involved in the transition from vegetative growth to flowering (Fornara et al. (2004) Plant Physiol 135 (4): 2207-19). The constitutive overexpression of OsMADS18 in rice, dwarfs the plants and makes them bloom early as a consequence of the accelerated maturation of the plant. In yeast two hybrid experiments, it has been shown that OsMADS18 forms heterodimers with OsMADS6, OsMADS24, OsMADS45 and OsMADS47. It also interacts specifically with the OsNF-YBl, which shares the highest sequence identity with the Cotyledon 1 of Arabidopsis Leaves (LEC1 or AtNF-YB9). The formation of the ternary complex between the three proteins 0sMADS18, 0sMADS6 and OsNF-YBl (Masiero et al. (2002) J Biol Chem 277 (29): 26429-35) has also been shown. In US 6,229,068 Bl, Yanofsky et al., Describes a method for increasing the size of the seed (or fruit) in a plant using a genetic product related to the AGL8 and expressing it ectopically in the plant. The preferred regulatory elements mentioned in the document for the ectopic expression of a gene product related to the AGL8 are constitutive, inducible or preferred seed elements. The international patent application WO 02/33091 describes a MADS-box transcription factor of monocotyledon (of English ryegrass) for the manipulation of the flowering and architecture of the plant. International patent application WO 03/057877 describes a MADS-box cDNA having a single nucleotide polymorphism (SNP) among different varieties of barley. According to one embodiment of the present invention, there is provided a method for increasing the yield of plants, which comprises increasing the activity in a plant of a polypeptide similar to 0sMADS18 or a homologue thereof, which polypeptide similar to 0sMADS18 or homologue same, it is: (i) MADS-box type II transcription factor of monocotyledonous SQUAMOSA; and (ii) it has DNA and DNA and protein binding activity; and (iii) comprises the LPP MLRT motif (SEQ ID NO: 18) in the last 15 amino acids of the C-terminal end of the protein, allowing amino acid substitution anywhere in the motif but not in the second and fourth positions of the motif, which are respectively a proline and a tryptophan; and (iv) has at least 65% sequence identity with the Os ADSl8 protein of SEQ. ID. NO: 2. Advantageously, the performance of the methods according to the present invention results in plants having increased yield, particularly seed yield. The term "increased yield" as defined herein is considered to mean an increase in any one or more of the following, each in relation to the corresponding wild plants: (i) increased biomass (weight) of one or more parts of a plant, particularly parts on the ground (harvestable) or increased biomass of any harvestable part; (ii) increased seed yield; which includes an increase in seed biomass (seed weight) and which may be an increase in seed weight per plant or on an individual seed basis or an increase in seed weight per hectare or acre; (iii) increased number of flowers (florets) per panicle, which is expressed as a ratio of the number of filled seeds to the number of primary panicles; (iv) increased number of seeds (stuffed); (v) increased seed filling ratio (which is the number of filled seeds divided by the total number of seeds and multiplied by 100); (vi) increased seed size, which can also influence the composition of the seeds; (vii) increased seed volume, which may also influence the composition of the seeds (for example due to an increase in the amount or a change in the composition of oil, protein or carbohydrate); (viii) increased area of seed; (ix) increased length of seed; (x) increased perimeter of seed; (xi) increased harvest index, which is expressed as a ratio of the yield of harvestable parts, such as seeds, to total biomass; and (xii) increased weight of thousands of seeds (TKW), which is extrapolated from the number of seeds filled, quantified and their total weight. An increased TKW may result in an increased size of seed and / or increased seed weight and may also result in an increase in embryo size and / or size of the endosperm. Taking corn as an example, an increase in yield may manifest itself as one or more of the following: increase in the number of plants per hectare or acre, an increase in the number of spikes per plant, an increase in the number of rows , number of seeds per row, weight of the seeds, weight of thousands of seeds, length / diameter of the ears, among others. Taking rice as an example, an increase in yield can be manifested by an increase in one or more of the following: number of plants per hectare or acre, number of panicles per plant, number of spikelets per panicle, number of flowers per panicle, increase in the ratio of seed filling, increase in the weight of thousands of seeds, among others. An increase in performance can result in a modified architecture, or it can occur as a result of a modified architecture. DESCRIPTION OF THE INVENTION According to a preferred aspect, the performance of the methods of the invention results in plants having increased seed yield. Therefore, in accordance with the present invention, there is provided a method for increasing the yield of plant seeds, which method comprises increasing the activity in a plant of a polypep similar to 0sMADS18 or a homologue thereof. Since the transgenic plants in accordance with the present invention, have an increased yield, it is likely that these plants exhibit an increased relationship of growth (during at least part of their life cycle), in relation to the growth rate of the corresponding wild plants at a corresponding stage in their life cycle . The increased growth ratio may be specific to one or more parts of a plant (including the seeds), or may be substantially throughout the plant. A plant that has an increased growth relationship may even exhibit early flowering. The increase in the growth ratio can take place in one or more stages in the life cycle of a plant or substantially during the entire life cycle of the plant. The increased relationship of growth during the early stages in the life cycle of a plant may reflect improved vigor. The increase in the growth ratio can alter the harvest cycle of a plant allowing planting later and / or harvesting before it could be possible. If the growth ratio is increased enough, it can allow the subsequent planting of seeds of the same plant species (for example planting and harvesting of rice plants followed by sowing and harvesting of additional rice plants all within a conventional growth period). Also, if the growth ratio is increased enough, it can allow a subsequent seeding of seeds of different plant species (for example the planting and harvesting of rice plants followed, for example, by the optional planting and harvesting of beans). soy, potato or any other suitable plant). Additional harvest times of the same rhizome may also be possible in the case of some crop plants. Altering the harvest cycle of a plant can lead to an increase in annual biomass production per acre (due to an increase in the number of times (say for example in a year) that any particular plant can grow and be harvested). An increase in the growth ratio may also allow the cultivation of transgenic plants in a wider geographical area than their wild-type counterparts, since the territorial limits for cultivating a crop are often determined by environmental, adverse conditions, whether in planting time (early season) or harvest time (late season). Such adverse conditions can be avoided if the harvest cycle is shortened. The growth relationship can be determined by deriving several parameters of the growth curves, such parameters can be: T-Mid (the time it takes the plants to reach 50% of their maximum size) and T-90 (the time takes plants reach 90% of their maximum size), among others. The carrying out of the methods of the invention gives plants that have an increased growth ratio. Therefore, in accordance with the present invention, there is provided a method for increasing yield in plants, which method comprises increasing the activity in a plant of a polypeptide similar to 0s ADS18 or a homologue thereof. An increase in yield and / or growth ratio occurs if the plant is under non-stressed conditions or if the plant is exposed to several stressed conditions compared to the wild type / control plants. Plants typically respond to exposure to stressed conditions by making them grow more slowly. In conditions of severe stress, the plant can even stop its growth completely. On the other hand the condition of moderate stress is defined herein as any stress to which a plant is exposed which does not result in the plant ceasing to grow completely without the ability to resume growth. Due to advances in agricultural practices (irrigation, fertilization, pesticide treatments), severe stress conditions are often not found in crop plants, cultivated. As a consequence, committed growth induced by moderate stress conditions is often an undesirable aspect of agriculture. The conditions of moderate stress are the typical stress conditions to which a plant can be exposed. These stress conditions can be stress conditions (environmental), biotic and / or abiotic, daily. Typical abiotic or environmental stress conditions include temperature stress conditions, caused by atypical temperatures of heat or cold / freezing; salt stress condition; Water stress condition (drought or excess water). Chemical substances can also cause abiotic stress conditions. Abiotic stress conditions are typically those stress conditions, caused by pathogens, such as bacteria, viruses, fungi and insects. The aforementioned increases in yield can advantageously be obtained in any plant during the execution of the methods of the invention. The term "plant" as used herein encompasses whole plants, progenitors and the progeny of the plants and parts of the plant, including seeds, shoots, stems, leaves, roots (including tubers), flowers, and tissues and Organs, wherein each of the aforementioned comprises the gene / nucleic acid of interest. The term "plant" also encompasses plant cells, suspension cultures, callus tissue, embryos, meristematic regions, gametophytes, sporophytes, pollen, and microspores, again wherein each of the aforementioned comprises the gene / nucleic acid of interest. Plants that are particularly useful in the methods of the invention include all plants belonging to the Viridiplantae super family, in particular monocotyledonous and dicotyledonous plants which include forage grass or legumes, ornamental plants, food crops, trees or shrubs selected from the list comprising Acacia spp. , Acer spp. , Actinidia spp. , Aesculus spp. , Agathis australis, Albizia amara, Alsophila tricolor, Andropogon spp., Arachis spp, Areca catechu, Astelia fragrans, AsLragalus cicer, Baikiaea plurijuga, Betula spp., Brassica spp., Bruguiera gymnorrhiza, Burkea africana, Butea leafy, Cadaba farinosa, Calliandra spp, Camellia sinensis, Canna indica, Capsicum spp., Cassia spp., Centroema pubescens, Chaenomeles spp., Cinnamomum cassia, Coffea arabica, Colophospermum mopane, Coronillia varia, Cotoneaster serotype, Crataegus spp. , Cucumis spp. , Cupressus spp. , Cyathea dealbata, Cydonia oblonga, Cryptomeria japonica, Cymbopogon spp. , Cynthea dealbata, Cydonia oblonga, Dalbergia monetaria, Davallia divaricata, Desmodium spp., Dicksonia squarosa, Diheteropogon amplectens, Dioclea spp, Dolíchos spp., Dorycnium rectu, Echinochloa pyramidalis, Ehrartia spp., Eleusine coracana, Eragrestis spp., Erythrina spp. , Eucalyptus spp., Euclea schimperi, Eulalia villosa, Fagopyrum spp., Feijoa sellowiana, Fragaria spp., Flemingia spp, Freycinetia banksii, Geranium thunbergii, Ginkgo biloba, Glycine javanica, Gliricidia spp, Gossypium hirsutum, Grevillea spp., Guibourtia coleosperma, Hedysaru spp., Hemarthia altissima, Heteropogon contortus, Hordeu vulgare, Hyparrhenia rufa, Hypericum erectum, Hyperthelia dissoluta, Indigo incarnata, Iris spp., Leptarrhena pyrolifolia, Lespediza spp., Lettuca spp., Leucaena leucocephala, Loudetia simplex, Lotonus baínesii, Lotus spp., Macrotyloma axillare, Malus spp., Manihot esculenta, Medicago sativa, Metasequoia glyptostroboides, Musa sapientum, Nicotianu spp., Onobrychis spp., Ornithop Us spp., Oryza spp., Peltophorum africanum, Pennisetum spp., Persea gratissi a, Petunia spp., Phaseolus spp., Phoenix canariensis, Phormium cookianum, Photinia spp., Picea glauca, Pinus spp., Pisum sativum, Podocarpus totara, Pogonarthria fleckii, Pogonarthria squarrosa, Populus spp., Prosopis cineraria, Pseudotsuga menziesii, Pterolobium stellatum, Pyrus com unis, Quercus spp. , Rhaphiolepsis umbellata, Rhopalostylis sapida, Rhus natalensis, Ribes grossularia, Ribes spp. , Robinia pseudoacacia, Rosa spp., Rubus spp., Salix spp., Schyzachyrium sanguineum, Sciadopitys verticillata, Sequoia se pervirens, Sequoiadendron giganteu, Sorghum bicolor, Spinacia spp. , Sporobolus firnbriatus, Stiburus alopecuroides, Stylosanthos humilis, Tadehagi spp, Taxodium distichum, Themeda triandra, Trifolium spp. , Triticum spp. , Tsuga heterophylla, Vaccinium spp. , Vicia spp., Vitis vinifera, Watsonia pyramidata, Zantedeschia aethiopica, Zea mays, amaranth, artichoke, asparagus, broccoli, cabbage of Brúcelas, cabbage, cañola, carrot, cauliflower, celery, smooth leafy cabbage, flax, pecunia, lentil, rapeseed oilseed , okra, onion, potato, rice, soy, strawberry, sugar beet, sugar cane, sunflower, tomato, pumpkin, tea and seaweed, among others. According to a preferred embodiment of the present invention, the plant is a crop plant such as soybean, sunflower, cañola, alfalfa, rapeseed, cotton, tomato, potato or tobacco. Further preferably, the plant is a monocotyledonous plant, such as sugarcane. More preferably the plant is a cereal, such as rice, corn, wheat, barley, millet, rye, sorghum or oats. 1 The activity of a polypeptide similar to 0sMADS18 can be increased by raising the levels of the polypeptide. Ms levels of 0sMADS18 can also be increased. Alternatively, activity may also be increased when there is no change in the levels of a polypeptide similar to 0sMADS18, or even when there is a reduction in the levels of a polypeptide similar to 0sMADS18. This can occur when the intrinsic properties of the polypeptide are altered, for example, by making mutant versions that are more active than the wild-type polypeptide. The term "OsMADS18-like polypeptide or a homolog thereof" as defined herein, refers to a polypeptide (i) that is a MADS-box monocotyledonous transcription factor of the SQUA OSA member; and (ii) having DNA and protein binding activity; and (iii) comprising the motif LPPWMLRT (SEQ ID NO: 18) in the last 15 amino acids of the C-terminal end of the protein, which allows substitution of amino acids anywhere in the motif but not in the second and fourth positions of the motif, which are respectively a proline and a tryptophan; and (iv) having at least 65% sequence identity with the 0sMADS18 protein of SEQ. ID. NO: 2. The substitution in the motive may be a conservative constitution although it is not limited to conservative substitutions. The conservative amino acid substitution can replace any one or more of the amino acid residues of the aforementioned motif, which includes positions 2 and 4 which are occupied by proline and tryptophan respectively. The following table gives examples of conserved amino acid substitutions. Table 1: Examples of conserved amino acid substitutions Residual Conservative Substitutions Residual Conservative Substitutions Ala Ser Leu lie; Val Arg Lys Lys Arg; Gln Asn Gln; His Met Leu; lie Asp Glu Phe Met; Leu; Tyr Cys Ser Thr Ser; Val Glu Pro Tyr Tyr Gly Pro Tyr Trp; Phe His Asn; Gln Val lie; Leu lie Leu; Val A "polypeptide similar to OsMADSl 3 or a homologue thereof" can be easily identified using routine techniques well known in the art. For example, DNA binding activity and protein-protein interactions can be easily determined in vitro or in vivo using techniques well known in the art. Examples of in vitro assays for DNA linker activity include: gel delay analysis using known MADS-box DNA binding domains (West et al. (1998) Nucí Acid Res 26 (23): 5277-87) , or trials with a single yeast hybrid. An example of an in vitro assay for protein-protein interactions is the analysis with two yeast hybrids (Fields and Song (1989) Nature 340: 245-6). In addition, the previously defined motif (SEQ ID NO: 18) can also be easily identified by a person skilled in the art, by simply making an alignment and looking for the motif at the C-terminal end of a polypeptide. Also, a polypeptide having at least 65% identity with the amino acid sequence represented by SEQ. ID. NO: 2, can also be easily established by sequence alignment. Methods for alignment of sequences for comparison are well known in the art, such methods include GAP, BESTFIT, BLAST, FASTA and TFASTA. The GAP uses the algorithm of Needleman and Wunsch ((1970) J Mol Biol 48: 443-453) to find the alignment of two complete sequences that minimizes the number of matches and minimizes the number of empty spaces. The BLAST algorithm (Altschul et al (1990) J Mol Biol 215: 403-10) calculates the percentage of sequence identity and performs a statistical analysis of the similarity between the two sequences. The computer program to perform the BLAST analysis is available to the general public through the National Center for Biotechnology Information. Homologs of 0sMADS18 comprising the LPP motif LRT (SEQ ID NO: 18) within the last 15 amino acids of the protein, and having at least 65% identity with the amino acid sequences represented by SEQ. ID. NO: 2, can be easily identified using, for example, the algorithm for multiple sequence alignment ClustalW (version 1.83) available at http://clustalw.genome.jp/sit-bin/nph-clustalw, with the following alignment parameters in pairs: K-tuple size (word) of 1, window size of 5, penalty for empty space of 4, upper diagonal number of 5, and a percentage scoring method. Examples of plant-derived polypeptides, encompassed by the term "polypeptide similar to 0sMADS18 or a homologue thereof", include (see also Table 2): Oryza sativa (SEQ ID NO: 2), ZMM28 (or m28) AJ430695 from Zea mays (SEQ ID NO: 4), MADS3 AY198328 from Lolium perenne (SEQ ID NO: 6), m3 AJ249143 from Hordeum vulgare (SEQ ID NO: 8). A protein similar to ZMM28 was deduced from a contiguity of several overlapping ESTs of Saccharum officinarum, CA285442 (SEQ ID NO: 9), CA200888 (SEQ ID NO: 10), CA247266 (SEQ ID NO: 11) ), CA282968 (SEQ ID NO: 12), and CA299090 (SEQ ID NO: 13). The Saccharum officinarum protein (SEQ ID NO: 15) was deduced from the consensus sequence (SEQ ID NO: 14), 2 obtained by aligning five different ESTs. The SEQ. ID. NO: 16 is a nucleotide consensus sequence with a nucleotide change (G to T) at the 578 bp position of the ATG, compared to the SEQ. ID. NO: 14. The SEQ. ID. NO: 17 polypeptides were deduced from SEQ. ID. NO: 16, and is identical to SEQ. ID. NO: 15 except for an amino acid change at position 193 of the protein (V193G). Table 2: Examples of monocot orthologs similar to 0SMADS18 It is understood that the sequences that fall under the definition of "polypeptide similar to OsMADS18 or a homologue thereof", are not limited to the sequences represented by SEQ. ID. NO: 2, SEQ. ID. NO: 4, SEQ. ID. NO: 6, SEQ. ID. NO: 8, SEQ. ID. NO: 15 or SEQ. ID. NO: 17, although any polypeptide meets the criteria of: (i) being a MADS-box monocotyledonous transcription factor of SQUAMOSA; and (ii) have DNA and protein linker activity; and (iii) comprising the motif LPPWMLRT (SEQ ID NO: 18) in the last 15 amino acids at the C-terminal end of the protein, which allows a substitution of amino acids in any part of the motif but not in the second and fourth positions of the motif, which are respectively a proline and a tryptophan; and (iv) have at least 65% sequence identity with the 0sMADS18 protein of SEQ. ID. NO: 2 may be suitable for use in the methods of the invention and for obtaining plants that have increased yield in relation to the corresponding wild plants. The nucleic acid encoding the polypeptide similar to 0sMADS18 or a homologue thereof, can be any natural or synthetic nucleic acid. Therefore, the term "nucleic acid / gene similar to OsMADS18" as defined herein is any nucleic acid / gene encoding a polypeptide similar to OsMADS18 or a homologue thereof as defined herein above. Examples of nucleic acids similar to OsMADS18, include those represented by any of SEQ. ID. NO: 1, SEQ. ID. NO: 3, SEQ. ID. NO: 5, SEQ. ID. NO: 7, SEQ. ID. NO: 14 and SEQ. ID. NO: 16. Nucleic acids / genes similar to 0sMADS18 and variants thereof, may be suitable for carrying out the methods of the invention. Nucleic acids / genes similar to 0sMADS18 include portions of a nucleic acid / gene similar to 0sMADS18 and / or nucleic acids capable of hybridizing to a nucleic acid / gene similar to 0SMADS18. The term "portion" as defined herein refers to a piece of DNA (a nucleic acid / gene similar to 0sMADS18) comprising at least 747 nucleotides, which portion encodes a polypeptide of at least 249 amino acids, which polypeptide comprises minus features (i) and (ii) as follows, preferably together with characteristic (iii) and / or characteristic (iv), characteristics (i) to (iv) that is: (i) a transcription factor of monocotyledon type II MADS-box from Ciado SQUAMOSA; (ii) having DNA and protein linker activity; and (iii) comprising the motif LPPWMLRT (SEQ ID NO: 18) in the last 15 amino acids of the C-terminal end of the protein, which allows substitution of amino acids anywhere in the motif but not in the second and fourth positions of the motif, which are respectively a proline and a tryptophan; and (iv) having at least 65% sequence identity with the OsMADS18 protein of SEQ. ID. NO: 2. A portion can be prepared, for example, by making one or more deletions to a nucleic acid similar to OsMADS18. The portions can be used in isolation or they can be fused with other coding (or not coding) sequences in order, for example, to produce a protein that combines several activities. When fused with other coding sequences, the resulting polypeptide, produced in the translation, may be larger than that predicted for the fragment similar to 0s ADS18. Preferably, the functional portion is a portion of a nucleic acid as represented by any of SEQ. ID. NO: 1, SEQ. ID. NO: 3, SEQ. ID. NO: 5, SEQ. ID. NO: 7, SEQ. ID. NO: 14 and SEQ. ID. NO: 16. Another variant of a nucleic acid / gene similar to OsMADS18 is a nucleic acid capable of hybridizing under conditions of reduced stringency, preferably under severe conditions, with a nucleic acid / gene similar to 0sMADS18 as defined herein above, which hybridization sequence encodes a polypeptide comprising at least features (i) and (ii) as follows, preferably together with characteristic (iii) and / or characteristic (iv), characteristics (i) to (iv), is : (i) a MADS-box type II monocot transcription factor from the SQUAMOSA; and (ii) a polypeptide having DNA and protein linker activity; and (iii) a polypeptide comprising the motif LPPWMLRT (SEQ ID NO: 18), located in the last 15 amino acids of the protein, which allows a substitution of amino acids anywhere in the motif but not in the second and fourth positions of the motif, which are respectively a proline and a tryptophan; and (iv) having at least 65% sequence identity with the 0sMADS18 protein of SEQ. ID. NO: 2. In addition to having the aforementioned characteristics, preferably the hybridization sequence is one that is capable of hybridizing with a nucleic acid as represented by any of SEQ. ID. NO: 1, SEQ. ID. NO: 3, SEQ. ID. NO: 5, SEQ. ID. NO: 7, SEQ. ID. NO: 14, and SEQ. ID. NO: 16, or with a portion of any of the aforementioned sequences as defined herein above. The term "hybridization" as defined herein, is a process wherein complementary, substantially homologous nucleotide sequences are recombined in the form of a double strand to each other. The hybridization process can occur entirely in solution, ie both complementary nucleic acids are in solution. The hybridization process can also occur with one of the complementary nucleic acids, immobilized in a matrix such as magnetic beads, Sepharose beads or any other resin. The hybridization process can also take place with one of the immobilized complementary nucleic acids. on a solid support such as a nitro-cellulose or nylon membrane, or immobilized for example by photolithography on, for example, a siliceous glass support (the latter known as arrays or micro-arrays of nucleic acid or as nucleic acid fragments) ). In order to allow hybridization to take place, the nucleic acid molecules are usually denatured thermally or chemically to melt a double strand into two individual strands and / or to remove the forks or other secondary structures of the nucleic acids from a single strand The severity of the hybridization is influenced by conditions such as temperature, salt concentration, ionic strength and hybridization buffer composition. "Severe hybridization conditions" and "severe hybridization washing conditions" in the context of nucleic acid hybridization experiments, such as Southern and Northern hybridizations, depend on the sequence and differ under different environmental parameters. The skilled worker is aware of several parameters which can be altered during hybridization and washing either to maintain or change severity conditions. The Tm is the temperature under defined ionic strength and pH, at which 50% of the target sequence is hybridized to a perfectly coupled probe. The Tm depends on the conditions of the solution and the base composition and length of the probe. For example, longer sequences hybridize specifically at higher temperatures. The maximum hybridization ratio is obtained from approximately 16 ° C to 32 ° C below the Tm. The presence of monovalent cations in the hybridization solution reduces the electrostatic repulsion between the two strands of nucleic acid thus promoting a hybrid formation; this effect is visible for sodium concentrations of up to 0.4M. Formamide reduces the fusion temperature of DNA-DNA and DNA-RNA duplexes with 0.6 to 0.7 ° C for each percentage of formamide, and in addition 50% of formamide allows hybridization at 30 to 45 ° C, notwithstanding the Hybridization ratio will be reduced. Mismatches of base pairs reduce the hybridization ratio and thermal stability of the duplices. On average and for large probes, the Tm is decreased by approximately 1 ° C per% base mismatch. The Tm can be calculated using the following equations, depending on the types of hybrids: 1. DNA-DNA hybrids (Meinkoth and Wahl, Anal. Biochem., 138: 267-284, 1984): Tm = 81.5 ° C + 16.6xlog [Na +] a + 0.41x% [G / Cb] - 500x [Lc] _1 - 0.61x% formamide 2. DNA-RNA or RNA-RNA hybrids: Tm = 79.8 + 18.5 (log10 [Na +] a) + 0.58 (% G / Cb) + 11.8 (% G / Cb) 2 - 820 / Lc 3. Oligo-DNA or oligo-ARNd hybrids: For < 20 nucleotides: Tm = 2 (ln) For 20-35 nucleotides: Tm = 22 + 1.46 (ln) ao for another monovalent cation, but only accurate in the range of 0.01-0.4 b only accurate for% GC in the range of 30 % to 75%. c L = length of duplex in base pairs. d Oligo, oligonucleotide; ln, effective length of primer = 2x (No. of G / C) + (No. of A / T). Note: for each 1% of formamide, the Tm is reduced from approximately 0.6 to 0.7 ° C, while the presence of 6 M urea reduces the Tm to approximately 30 ° C. Hybridization specificity is typically the function of post-hybridization washes. To remove the background resulting from non-specific hybridization, the samples were washed with diluted salt solutions. Critical factors for such washes include the ionic strength and temperature of the final wash solution: the lowest salt concentration and the highest wash temperature, the highest wash severity. Washing conditions are typically performed at or below the severity of hybridization. Generally, severe conditions, suitable for nucleic acid hybridization assays or gene amplification detection methods, are as set forth above. Conditions of greater or lesser severity can also be selected. Usually, the low severity conditions that are selected are approximately 50 ° C lower than the thermal melting point (Tm) for the specific sequence at a defined ionic strength and pH. The conditions of medium severity are when the temperature is 20 ° C below the Tm, and the conditions of high severity are when the temperature is 10 ° C below the Tm. For example, severe conditions are those that are at least as severe as, for example, conditions A-L; and the conditions of reduced severity are at least as severe as, for example, the M-R conditions. The non-specific binding can be controlled using any of a number of known techniques such as, for example, blocking the membrane with solutions containing proteins, RNA, DNA, heterologous, and SDS additions to the hybridization buffer, and RNAse treatment. Examples of hybridization and washing conditions are listed in Table 3 below.

Table 3: Examples of hybridization and washing conditions "Hybrid length" is the anticipated length for nucleic acid hybridization. When the nucleic acids of known sequence hybridize, the length of the hybrid can be determined by aligning the sequences and identifying the conserved regions described herein. † SSPE (lxSSPE is 0.15 M NaCl, 10 mM NaH2P04, and 1.25 mM EDTA, pH 7.4) can be replaced by SSC (lxSSC is 0.15 M NaCl and 15 mM sodium citrate) in solutions of hybridization buffers and washing; the washes are performed for 15 minutes after the hybridization is complete. Hybridizations and further washing may include 5 × Denhardt's reagent, 0.5-1.0% SDS, 100 g / ml salmon sperm DNA, fragmented, denatured, 0.5% sodium pyrophosphate, and up to 50% formamide. * Tb-Tr: The hybridization temperature for the anticipated hybrids will be less than 50 base pairs in length, it should be 5-10 ° C less than the melting temperature Tm of the hybrids; Tm is determined according to the aforementioned equations. * The present invention also encompasses the substitution of any, or more, hybrid DNA or RNA partners with either a PNA, or a modified nucleic acid. For the purpose of defining the level of severity, reference can be made to Sambrook et al. (2001) Molecular Cloning: a laboratory manual, 3rd Edition Cold Spring Harbor Laboratory Press, CSH, New York or Current Protocols in Molecular Biology, John Wiley & Sons, N.Y. (1989). The nucleic acid similar to OsMADS18 or variant thereof can be derived from any natural or artificial source. The nucleic acid / gene or variant thereof can be isolated from a microbial source, such as yeast or fungus, or from a source of plant, algae or animal (including human). This nucleic acid can be modified from its natural form in composition and / or genomic environment through deliberate human manipulation. The nucleic acid can be isolated from a monocotyledonous species, preferably from the Poaceae family, preferably in addition to Oryza sativa. More preferably, nucleic acid similar to 0sMADS18, isolated from Oryza sativa, is represented by SEQ. ID. NO: 1 and the amino acid sequence similar to 0sMADS18, is as represented by SEQ. ID. NO: 2. The activity of a polypeptide similar to 0sMADS18 or a homologue thereof can be increased by introducing a genetic modification (preferably at the locus of a gene similar to 0sMADS18). The locus of a gene as defined herein is considered to mean a genomic region, which includes the gene of interest and 10 kb upstream or downstream of the coding region. Genetic modification can be introduced, for example, by any (or more) of the following methods: T-DNA activation, TILLING, site-directed mutagenesis, directed evolution, homologous recombination or by introducing and expressing in a plant a nucleic acid encoding a similar polypeptide to 0sMADS18 or a counterpart of it. After the introduction of the genetic modification, a step of selecting the increased activity of a polypeptide similar to 0sMADS18 follows, which increases the activity of plants that have an increased yield. The T-DNA activation label (Hayashi et al., Science (1992) 1350-1353) involves the insertion of T-DNA, which usually contains a promoter (it can also be a translation enhancer or an intron), in the genomic region of the gene of interest or 10 kb upstream or downstream of the coding region of a gene in a configuration such that the promoter directs the expression of the particular gene. Typically, the regulation of expression of the particular gene by its natural promoter is destabilized and the gene falls under the control of the newly introduced promoter. The promoter is typically embedded in a T-DNA. This T-DNA is inserted randomly into the genome of the plant, for example, through infection with Agrobacterium and leads to over-expression of genes near the inserted T-DNA. The resulting transgenic plants show dominant phenotypes due to over-expression of the genes close to the introduced promoter. The promoter to be introduced can be any promoter capable of directing the expression of a gene in the desired organism, in this case a plant. For example, constitutive, preferred tissue, cell-type and inducible promoters are completely suitable for use in the activation of T-DNA. A genetic modification can also be introduced into the locus of a gene similar to OsMADS18 using the TILLING technique (Targeted Induced Local Lesions in Genomes) Induced Local Lesions, Focused on Genomes). This mutagenesis technology is useful for generating, identifying and isolating mutagenized variants of a nucleic acid similar to 0sMADS18 capable of exhibiting activity similar to 0sMADS18. TILLING also allows the selection of plants that carry such mutant variants. These mutant variants may even exhibit activity similar to 0sMADS18 greater than that exhibited by the gene in its natural form. TILLING combines high-density mutagenesis with high-throughput screening methods. The steps typically followed in the TILLING are: (a) EMS mutagenesis (Redei GP and Koncz C (1992) in Methods in Arabidopsis Research, Koncz C, Chua NH, Schell J, eds. Singapore, World Scientific Publishing Co, pp. 16-82; Feldmann et al., (1994) In eyerowitz EM, Somerville CR, eds, Arabidopsis. Cold Spring Harbor Laboratory Press, Cold Spring Harbor, NY, pp. 137-172; Lightner J and Caspar T (1998) In J Martinez-Zapater, J Salinas, eds, Methods on Molecular Biology, Vol. 82. Humana Press, Totowa, NJ, pp. 91-104); (b) DNA preparation and grouping of individuals; (c) PCR amplification of a region of interest; (d) denaturing and re-combining to allow the formation of hetero-doubles; (e) DHPLC, where the presence of a heteroduplex in a collection is detected as an extra peak in the chromatogram; (f) identification of the mutant individual; and (g) sequencing of the mutant PCR product. Methods for TILLING are well known in the art (McCallum et al., (2000) Nat Biotechnol 18: 455-457, reviewed by Stemple (2004) Nat Rev Genet 5 (2): 145-50). Site-directed mutagenesis can be used to generate nucleic acid variants similar to 0sMADS18. Several methods are available to achieve targeted mutagenesis, the most common are PCR-based methods (current protocols in molecular biology, Wiley Eds. Http: // www .4ulr.com/products/currentprotocols/index.html). Directed evolution can also be used to generate nucleic acid variants similar to OsMADS18. This consists of iterations of DNA restructuring followed by appropriate selection and / or selection to generate nucleic acid variants similar to 0sMADS18 or variants thereof encoding polypeptides similar to 0sMADS18 or homologues thereof having a biological activity , modified (Castle et al., (2004) Science 304 (5674): 1151-4, US patents 5,811,238 and 6,395,547). The activity of T-DNA, TILLING, directed mutagenesis, and directed evolution, are examples of technologies that make possible the generation of new alleles and variants similar to 0sMADS18. Homologous recombination allows the introduction into a genome of a selected nucleic acid at a selected, defined position. Homologous recombination is a standard technology routinely used in biological sciences for lower organisms such as yeasts or Physco itrella moss. Methods for performing homologous recombination in plants have been described not only for model plants (Offringa et al (1990) EMBO J 9 (10): 3077-84) but also for crop plants, for example rice (Terada et al. (2002) Nat Biotech 20 (10): 1030-4; Iida and Terada (2004) Curr Opin Biotech 15 (2): 132-8). The nucleic acid to be considered as target (which may be a nucleic acid similar to OsMADS18 or variant thereof as defined herein above) does not need to be targeted to the locus of a gene similar to 0sMADS18, although it can be introduced, for example, in regions of high expression. The nucleic acid to be considered as the target may be an improved allele used to replace the endogenous gene or it may also be introduced into the endogenous gene. According to a preferred embodiment of the invention, the yield of the plant can be improved by introducing and expressing in a plant a nucleic acid encoding a polypeptide similar to OsMADS18 or a homologue thereof. A preferred method for introducing a genetic modification (which in this case need not be at the locus of a gene similar to 0sMADS18) is to introduce and express in a plant a nucleic acid encoding a polypeptide similar to 0sMADS18 or a homologue thereof. A polypeptide similar to 0sMADS18 or a homologue thereof as mentioned above, is (i) a MADS-box type II monocot transcription factor of the SQUAMOSA molecule; and (ii) has DNA and protein linker activity; and (iii) comprises the motif LPPWMLRT (SEQ ID NO: 18) located in the last 15 amino acids of the protein, which allows a substitution of amino acids anywhere in the motif but not in the second and fourth positions of the motif, which are respectively a proline and a tryptophan; and (iv) has at least 65% sequence identity with the OsMADS18 protein of SEQ. ID. NO: 2. The nucleic acid to be introduced into a plant can be a full-length nucleic acid or it can be a portion or a hybridization sequence as defined above. The "homologs" of a protein encompass peptides, oligopeptides, polypeptides, proteins and enzymes that have substitutions, deletions and / or amino acid insertions, relative to the unmodified protein in question and that have biological and functional activity similar to the unmodified protein. from which they are derived. To produce such homologues, the amino acids of the protein can be replaced by other amino acids having similar properties (such as hydrophobicity, hydrophilicity, antigenicity, similar propensity to form or break helical structures or β-sheet structures). The conservative substitution tables are well known in the art (see for example Creighton (1984) Proteins, W.H. Freeman and Company, and Table 1 above). Also encompassed by the term "homologous" are two special forms of homology, which include orthologous sequences and paralogical sequences, which encompass evolutionary concepts used to describe ancestral gene relationships. The term "parologist" refers to duplicates of genes within the genome of a species that lead to parologous genes. The term "ortholog" refers to homologous genes in different organisms because of the evolution of species. Orthologs, for example, in other species of monocotyledonous plants can be easily found by performing a so-called reciprocal search for repulsion or comparison. This can be done by a first repulsion or comparison that involves repulsing a search sequence (eg, SEQ ID NO: 1 or SEQ ID NO: 2) against any sequence database, such as the database NCBI available to all public, which can be found at: http://www.ncbi.nlm.nih.gov. BLASTn or tBLASTX (using predetermined, standard values) can be used from a nucleotide sequence and BLASTP or TBLASTN can be used (using predetermined, standard values) starting from a protein sequence. The BLAST results can optionally be filtered. The sequences of results, whether filtered or unfiltered, are compared in the BLAST back (second comparison with BLAST) against the sequences of the same organism as the organism of the search sequence, (where the search sequence is SEQ. ID NO: 1 or SEQ ID NO: 2 and the second repulsion could then be against the sequences of Oryza sativa (rice)). The results of the first and second BLASTs are then compared. A parologist identifies whether a superior hit of the second repulsion or comparison is of the same species from which the search sequence is derived; an orthologous is identified if a superior hit is not of the same species from which the search sequence is derived. The top hits are those that have a low E value. The lowest E value, the most significant score (or in other words the lowest change that the hit found by chance). In the case of large families, ClustalW can be used, followed by a close binding hierarchy, to help visualize the grouping of related genes and identify orthologs and parologists. A homolog can be in the form of a "substitution variant" of a protein, i.e. where at least one residue in an amino acid sequence has been removed and a different residue in its place. Amino acid substitutions are typically individual residues, but can be grouped depending on functional limitations placed on the polypeptide; the insertions will usually be in the order of approximately 1 to 10 amino acid residues. Preferably substitutions comprise conservative amino acid substitutions. A homolog can also be in the form of an "insertion variant" of a protein, i.e. where one or more amino acid residues are introduced at a predetermined site in a protein. The inserts may comprise amino-terminal and / or carboxy-terminal fusions as well as intra-sequence insertions of single or multiple amino acids. Generally, insertions within the amino acid sequence will be smaller than amino- or carboxy-terminal fusions, on the order of about 1 to 10 residues. Examples of amino- or carboxy-terminal fusion proteins or peptides include the binding domain or activation domain of a transcriptional activator as used in the yeast two-hybrid system, phage coat proteins, (histidine) -6 -tag, glutathione S-transferase-tag, protein A, maltose-binding protein, dihydrofolate reductase, TAG_100_ epitope, c-myc epitope, FLAG® epitope, lacZ, CMP (calmodulin-binding peptide), HA epitope, epitope of protein C and epitope VSV. Homologs in the form of "deletion variants" of a protein, are characterized by the removal of one or more amino acids from a protein. The amino acid variants of a protein can be easily made using synthetic peptide techniques, known in the art, such as solid phase peptide synthesis and the like, or by manipulation of recombinant DNA. Methods for manipulating DNA sequences to produce substitution, insertion or deletion variants of a protein, well known in the art. For example, techniques for making substitution mutations at predetermined sites in DNA, well known to those skilled in the art, include M13 mutagenesis, in vitro mutagenesis of the T7 gene (USB, Cleveland, OH), QuickChange Directed Mutagenesis (Stratagene, San Diego, CA), directed mutagenesis mediated with PCR or other directed mutagenesis protocols.

The polypeptide similar to 0sMADS18 or homologue thereof can be a derivative. The "derivatives" include peptides, oligopeptides, polypeptides, proteins and enzymes, which comprise substitutions, deletions or additions of amino acid residues of natural origin, compared to the amino acid sequence of a naturally occurring form of the protein, for example, as presented in SEQ. ID. NO: 2. "Derivatives" of a protein encompass peptides, oligopeptides, polypeptides, proteins and enzymes, which may comprise altered, glycosylated or naturally occurring amino acid residues, compared to the amino acid sequence of a form of natural origin of the polypeptide. A derivative may also comprise one or more non-amino acid substituents in comparison to the amino acid substitution from which it is derived, for example a reporter molecule or another ligand, covalently or non-covalently linked to the amino acid sequence, such as a reporter molecule which is united to facilitate its detection, and amino acid residues of natural origin, in relation to the amino acid sequence of a protein of natural origin. The polypeptide similar to 0sMADS18 or homolog thereof can be encoded by an alternative splice variant of a nucleic acid / gene similar to 0sMADS18. The term "alternative splice variant" as used herein, encompasses variants of a nucleic acid sequence in which the selected introns and / or exons have been cut, replaced or added, or in which the introns have shortened or elongated. Such variants will be ones in which the biological activity of the protein is retained, which can be achieved by selectively retaining the functional segments of the protein. Such splice variants can be found in nature or can be made by man. Methods for making such splice variants are well known in the art. Preferred splice variants are splice variants of the nucleic acid represented by SEQ. ID. NO: 1, SEQ. ID. NO: 3, SEQ. ID. NO: 5, SEQ. ID. NO: 7, SEQ. ID. NO: 14 and SEQ. ID. NO: 16. Also preferred are splice variants that encode a polypeptide that comprises at least the characteristics (i) and (ii) as follows, preferably together with the characteristic (iii) and / or characteristic (iv), characteristics (i) to (iv), which is (i) a MADS-box type II monocot transcription factor of the SQUAMOSA molecule; (ii) having DNA and protein linker activity; and (iii) comprising the motif LPPWMLRT (SEQ ID NO: 18) located in the last 15 amino acids of the protein, which allows a substitution of amino acids anywhere in the motif but not in the second and fourth positions of the motif. , which are respectively a proline and a tryptophan; and (iv) having at least 65% sequence identity with the 0sMADS18 protein of SEQ. ID. NO: 2. The homolog can also be encoded by an allelic variant of a nucleic acid encoding a polypeptide similar to 0sMADS18 or a homologue thereof, preferably an allelic variant of a nucleic acid, represented by SEQ. ID. NO: 1, SEQ. ID. NO: 3, SEQ. ID. NO: 5, SEQ. ID. NO: 7, SEQ. ID. NO: 14 or SEQ. ID. NO: 16. Further preferably, the polypeptide encoded by the allelic variant comprises at least features (i) and (ii) as follows, preferably together with characteristic (iii) and / or characteristic (iv), characteristics (i) and (iv), which is: (i) a MADS-box type II monocot transcription factor from SQUAMOSA; (ii) having DNA and protein linker activity; and (iii) comprising the motif LPPWMLRT (SEQ ID NO: 18) located in the last 15 amino acids of the protein, which allows a substitution of amino acids anywhere in the motif but not in the second and fourth positions of the motif. , which are respectively a proline and a tryptophan; and (iv) having at least 65% sequence identity with the OsMADS18 protein of SEQ. ID. NO: 2. Allelic variants exist in nature and are encompassed within the methods of the present invention, the use of these natural alleles. Allelic variants include Single Nucleotide Polymorphism (SNPs), as well as Small Insertion / Elimination Polymorphisms (INDELs). The size of INDELs is usually less than 100 bp. The SNPs and INDELs form a larger set of sequence variants in polymorphic strains, of natural origin, of most organisms. According to a preferred aspect of the present invention, enhanced or increased expression of the nucleic acid similar to 0sMADS18 or variant thereof is conceived. Methods for obtaining improved or increased expression of genes or gene products are well documented in the art and include, for example, overexpression manipulated by appropriate promoters, the use of transcription enhancers or translation enhancers. The isolated nucleic acids which serve as promoter or enhancer elements can be introduced at an appropriate (typically upstream) position of a non-heterologous form of a polynucleotide to regulate the expression of a nucleic acid similar to 0sMADS18 or variant thereof. For example, endogenous promoters can be altered in vivo by mutation, elimination or substitution (see, Kmiec, US Pat. No. 5,565,350; Zarling et al., PCT / US93 / 03868), or isolated promoters can be introduced into a cell of the plant in the proper orientation and distance of a gene of the present invention, to control the expression of the gene. If expression of the polypeptide is desired, it is generally desirable to include a polyadenylation region at the 3 'end of a coding region of the Polynucleotide. The polyadenylation region can be derived from the natural gene, from a variety of other plant genes, or from T-DNA. The sequence of the 3 'end to be added may be derived, for example, from the genes of nopaline synthase or octopine synthase, or alternatively from another gene of the plant, or less preferably from any other eukaryotic gene. A sequence of introns can also be added to the 5 'untranslated region or the coding sequence of the partial coding sequence to increase the amount of mature message that accumulates in the cytosol. It has been shown that the inclusion of a spliced intron in the transcription unit in the expression constructs of plants and animals, increases the genetic expression at both mRNA and protein levels, up to 1000 times, Buchman and Berg, Mol. Cell biol. 8: 4395-4405 (1988); Callis et al., Genes Dev. 1: 1183-1200 (1987). Such introns improvement of gene expression is typically greater when placed near the 5 'end of the transcription unit. The use of maize introns, intron 1, 2, 6, of Adhl-S, the Bronze-1 intron, are well known in the art. See generally, The Maize Handbook, Chapter 116, Freeling and Walbot, Eds. , Springer, N.Y. (1994). The invention also provides genetic constructs and vectors to facilitate the introduction and / or expression of nucleotide sequences useful in the methods according to the invention to give plants having an increased yield relative to the corresponding wild plants. Therefore, a genetic construct is provided comprising: (i) a nucleic acid similar to 0sMADS18 or variant thereof; (ii) One or more control sequences capable of manipulating the expression of the nucleic acid sequence of (i); and optionally (iii) A transcription termination sequence. The constructs useful in the methods according to the present invention can be constructed using recombinant DNA technology well known to those skilled in the art. Genetic constructs can be inserted in vectors, which may be commercially available, suitable for transformation into plants and suitable for the expression of the gene of interest in the transformed cells. The plants are transformed with a vector comprising the sequence of interest (i.e., a nucleic acid similar to OsMADS18 or variant thereof). The sequence of interest is operably linked to one or more control sequences (at least one promoter). The terms "regulatory element", "control sequence" and "promoter" are all used interchangeably herein and will be understood in a broad context to refer to nucleic acid regulatory sequences, capable of effecting the expression of sequences to which they are linked. The aforementioned terms encompass regulatory, transcriptional sequences derived from a genomic, eukaryotic, classical gene (which includes the TATA box which is required for the exact start of transcription, with or without a sequence of the CCAAT box) and additional, regulatory elements ( ie upstream activation sequences, enhancers and silencers) which alter gene expression in response to the developmental and / or external stimulus, or in a tissue-specific manner. Also included within the term is a transcriptional regulatory sequence of a classical prokaryotic gene, in which case it may include a sequence of -35 box and / or regulatory sequences of box-10 transcripts. The term "regulatory element" also encompasses a synthetic fusion molecule or derivative that confers, activates or enhances the expression of a nucleic acid molecule in a cell, tissue or organ. The term "operably linked" as used herein, refers to a functional link between the promoter sequence and the gene of interest, such that the promoter sequence is capable of initiating transcription of the gene of interest. Nucleic acid similar to 0sMADS18 or variant thereof is therefore preferably operably linked to an apical meristem promoter of early regrowths. A "promoter of apical meristem of early regrowths" as defined herein is a promoter that is transcriptionally activated in the apical meristem of the regrowth of the globular stage of the embryo up to the stage of the young seedling; These steps are well known to those skilled in the art. Preferably, the early regrowth apical meristem promoter is an OSH1 promoter (rice; SEQ ID NO: 22 (Matsuoka et al., (1993) Plant Cell 5: 1039-1048; Sato et al., (1996)). Proc Nati Acad Sci USA 93 (15): 8117-22) It should be clarified that the applicability of the present invention is not restricted to the nucleic acid similar to OsMADS18 represented by SEQ ID NO: 1, nor the applicability of the invention is restricted to the expression of a nucleic acid similar to OsMADS18 when manipulated by an 0SH1 promoter Examples of early sprouted apical meristem promoters are shown in Table 4. These are members of the homeobox or homeodomain (sequence of about 180 base pairs near the 3 'end of certain homeotic genes) class 1 of the KOX family, of parologous or orthologous genes.It should be understood that the following list is not complete Table 4: Examples of apical meristem promoters early Optionally, one or more terminator sequences can also be used in the construct introduced in a plant. The term "terminator" encompasses a control sequence which is a DNA sequence at the end of a transcriptional unit which signals 3 'processing and polyadenylation of a primary transcript and transcription termination. Additional regulatory elements may include transcription as well as translation enhancers. Those skilled in the art will be aware of the terminator and enhancer sequences that may be suitable for use in the embodiment of the invention. Such sequences would be known or can be easily obtained by a person skilled in the art. The genetic constructs of the invention may also include a replication sequence origin that is required for maintenance and / or replication in a specific cell type. An example is when it is required to maintain a genetic construct in a bacterial cell as a genetic, episomal element (eg, plasmid or cosmid molecule). Preferred origins of replication include, but are not limited to, fl-ori and colEl. The genetic construct may optionally comprise a selectable marker gene. When used herein, the term "selectable marker gene" includes any gene that confers a phenotype on a cell in which it is expressed to facilitate the identification and / or selection of cells that are transfected or transformed with a construct. of nucleic acid of the invention. Suitable markers can be selected from markers that confer antibiotic resistance or herbicide, that introduce a new metabolic trait or that allow a visual selection. Examples of selectable marker genes include genes that confer resistance to antibiotics (such as nptll that phosphorylates neomycin and kanamycin, or hpt, which phosphorylates hygromycin), to herbicides (eg, bar which provides Basta resistance; or gox that provides resistance against glyphosate), or genes that provide a metabolic trait (such as manA that allows plants to use mannose as the sole source of carbon). Visual marker genes result in the formation of color (eg, β-glucuronidase, GUS) luminescence (such as luciferase) or fluorescence (Green Fluorescent Protein, GFP, and derivatives thereof). The present invention also encompasses plants obtainable by the methods according to the present invention. The present invention therefore provides plants obtainable by the methods according to the present invention, which plants have introduced therein a nucleic acid similar to OsMADS18 or variant thereof. The invention also provides a method for the production of transgenic plants that have an increased yield in relation to the corresponding wild plants, comprising the introduction and expression in a plant of a nucleic acid similar to 0sMADS18 or a variant thereof. More specifically, the present invention provides a method for the production of transgenic plants that have an increased yield in relation to the corresponding wild plants, which method comprises: (i) introducing and expressing in a plant, part of the plant or cell of the plant, a nucleic acid similar to 0sMADS18 or variant thereof; and (ii) cultivate the plant cell under conditions that promote the growth and development of the plant. The nucleic acid can be introduced directly into a cell of the plant or the plant itself (including introduction into a tissue, organ or any other part of a plant). According to a preferred feature of the present invention, the nucleic acid is preferably introduced into a plant by transformation. The term "transformation" as mentioned herein encompasses the transfer of an exogenous Polynucleotide into a host cell, regardless of the method used for the transfer. The tissue of the plant capable of clonal propagation, subsequent, either by organogenesis or embryogenesis, can be transformed with a genetic construct of the present invention and a whole plant regenerated therefrom. The particular tissue chosen will vary depending on the clonal propagation systems available for, and more in accordance with, the particular species being transformed. Exemplary tissue targets include discs or leaf slices, embryos, cotyledons, hypocotyls, mega-gametophytes, callus tissues, existing merismatic roof (eg, apical meristem, auxiliary buds, and root meristems), and induced meristem tissue (for example, cotyledon meristem and hypocotyl meristem). The polynucleotide can be introduced temporarily or stably into a host cell and can be maintained non-integrated, for example, as a plasmid. Alternatively, it can be integrated into the host genome. The resulting cell of the transformed plant can then be used to regenerate a transformed plant in a manner known to those skilled in the art. The transformation of the plant species is now a fairly routine technique. Advantageously, any of the various transformation methods can be used to introduce the gene of interest into a suitable predecessor cell. Transformation methods include the use of liposomes, electroporation, chemical substances that increase the absorption of free DNA, injection of DNA directly into the plant, bombardment with a genetic gun, transformation using viruses or pollen and microprojection. The methods can be selected from the method with calcium / polyethylene glycol for the protoplasts (Krens, F.A. et al., (1982) Nature 296, 72-74; Negrutiu I et al. (1987) Plant Mol Biol 8: 363-373); protoplast electroporation (Shillito R.D. et al., 1985 Bio / Technol 3, 1099-1102); micro-injection into the plant material (Crossway A et al., (1986) Mol Gen Genet 202: 179-185); bombardment of particles coated with DNA or RNA (Klein TM et al., (1987) Nature 327: 70) virus infection (non-integrators) and the like. Transgenic rice plants that express a nucleic acid / gene similar to 0sMADS18, preferably are produced through Agrobacterium-mediated transformation using any of the well-known methods for rice transformation, as described in any of the following: European patent application, published EP1198985 Al; Aldemita and Hodges (Planta 199: 612-617, 1996); Chan et al. (Plant Mol Biol 22 (3): 491-506, 1993); Hiei et al. (Plant J 6 (2): 271-282, 1994), which descriptions are incorporated herein by reference as if they were fully established. In the case of corn transformation, the preferred method is as described in Ishida et al. (Nat. Biotechnol 14 (6): 745-50, 1996) or Frame et al. (Plant Physiol 129 (1): 13-22, 2002), which descriptions are incorporated herein by reference as if they were fully established. Generally after transformation, the cells of the plant or cell clusters are selected for the presence of one or more markers which are encoded by genes expressible in plants co-transferred with the gene of interest, after which the transformed material It regenerates in a whole plant. After DNA transfer and regeneration, putatively transformed plants can be evaluated, for example using Southern analysis, for the presence of the gene of interest, copy number and / or genomic organization. Alternatively or additionally, the levels of expression of newly introduced DNA can be monitored using Northern and / or Western analysis, both techniques are well known to those of ordinary skill in the art. The transformed transformed plants can be propagated by a variety of means, such as by clonal propagation or classical breeding techniques. For example, a first generation (or TI) transformed plant can itself give homozygous second generation (or T2) transformants, and the T2 plants are also propagated through classical breeding techniques.

Transformed, generated organisms can take a variety of forms. For example, they may be chimeras of transformed cells and untransformed cells; clonal transformants (for example, all cells are transformed to contain the expression cassette); grafts of transformed and untransformed tissues (for example, in plants, a transformed rhizome grafted to an untransformed stem). The present invention clearly extends to any cell of the plant or plant produced by any of the methods described herein, and to all parts of the plant and propagules thereof. The present invention also extends to encompass the progeny of a primary, transformed or transfected cell, tissue, organ or whole plant that has been produced by any of the aforementioned methods, the only requirement is that the progeny exhibit the same (s) genotypic characteristic (s) and / or phenotypic (s) to those produced by the parent in the methods according to the invention. The invention also includes host cells that contain a nucleic acid similar to 0sMADS18, isolated, or variant thereof. The preferred host cells according to the invention are the cells of the plant. The invention also extends to harvestable parts of a plant such as, but not limited to seeds, leaves, fruits, flowers, stems, rhizomes, tubers and bulbs. The invention further relates to products derived from a harvestable part of such a plant, such as dry granules or powders, oil, fat and fatty acids, starch or proteins. The present invention also encompasses the use of nucleic acids similar to Os ADS18 or variants thereof and the use of polypeptides similar to 0sMADS18 or homologs thereof. Such use refers to improving the yield of the plant in relation to the corresponding wild plants, in particular to improve the yield of the seeds. The increase in performance is as defined herein above. Nucleic acids similar to 0sMADS18 or variants thereof, or polypeptides similar to 0sMADS18 or homologs thereof, may find use in reproduction programs in which a DNA marker is identified which can be genetically linked to a gene similar to 0sMADS18 or variant thereof. Nucleic acids / genes similar to 0sMADS18 or variants thereof, or polypeptides similar to OsMADS18 or homologs thereof, can be used to define a molecular marker. This DNA or protein marker can then be used in breeding programs to select plants that have increased yield. The gene similar to 0sMADS18 or variant thereof, for example, can be a nucleic acid as represented by any of SEQ. ID. NO: 1, SEQ. ID. NO: 3, SEQ. ID. NO: 5, SEQ. ID. NO: 7, SEQ. ID. NO: 14, and SEQ. ID. NO: 16. Allelic variants of a nucleic acid / gene similar to 0sMADS18 may also find use in marker-assisted reproduction programs. Such breeding programs sometimes require the introduction of allelic variation by the mutagenic treatment of the plants, using for example EMS mutagenesis; alternatively, the program may begin with a collection of allelic variants of the so-called "natural" origin unintentionally caused. The identification of allelic variants then takes place, for example, by PCR. This is followed by a step for the selection of higher allelic variants of the sequence in question and which give an increased performance. The selection is typically carried out by monitoring the performance performance of plants containing different allelic variants of the sequence in question, for example, allelic variants different from any of the SEQ. ID. NO: 1, SEQ. ID. NO: 3, SEQ. ID. NO: 5, SEQ. ID. NO: 7, SEQ. ID. NO: 14, and SEQ. ID. NO: 16. Performance performance can be monitored in a greenhouse or in the field. Optional, additional steps include crossing or fertilizing plants, in which the superior allelic variant was identified with another plant. This could be used, for example, to make a combination of phenotypic, interesting characteristics.

A nucleic acid similar to 0sMADS18 or variant thereof can also be used as probes to genetically and physically map the genes that are a part of, and as markers for traits linked to those genes. Such information may be useful in the reproduction of plants in order to develop lines with appropriate phenotypes. Such use of nucleic acids similar to OsMADS18 or variants thereof, requires only a nucleic acid sequence of at least 15 nucleotides in length. Nucleic acids similar to OsMADS18 or variants thereof, can be used as restriction fragment length polymorphism (RFLP) markers. Southern hybridization methods (Sambrook J, Fritsch EF and Maniatis T (1989) Molecular Cloning, A Laboratory Manual) of restriction-digested genomic DNA can be probed with nucleic acids similar to 0sMADS18 or variants thereof. The resulting band patterns can then be subjected to genetic analysis using computer programs such as MapMaker (Lander et al. (1987) Genomics 1: 174-181) in order to construct a genetic map. In addition, nucleic acids can be used to probe Southern hybridization methods containing genomic DNAs treated with restriction endonuclease from a set of individuals representing the progenitor and the progeny of a defined genetic cross. A segregation of the DNA polymorphisms is observed and used to calculate the position of the nucleic acid similar to the 0sMADS18 or variant thereof in the genetic map previously obtained using this population (Botstein et al. (1980) Am. J. Hum. Genet 32: 314-331). The production and use of probes derived from genes for use in genetic mapping is described in Bematzky and Tanksley (1986) Plant Mol. Biol. Repórter 4: 37-41. Numerous publications describe the genetic mapping of specific cDNA clones using the methodology generally described above or variations thereof. For example, inter-F2 populations, retro-crossing populations, random mating populations, nearby isogenic lines, and other sets of individuals can be used for mapping. Such methodologies are well known to those skilled in the art. Nucleic acid probes can also be used for physical mapping (ie, placement of sequences on physical maps; see Hoheisel et al., In: Non-marranalian Genomic Analysis: A Practical Guide, Academic Press 1996, pp. 319-346, and the references cited therein). In another embodiment, nucleic acid probes can be used in mapping with direct fluorescence in situ hybridization (FISH) (Trask (1991) Trends Genet 7: 149-154). Although current methods of FISH mapping favor the use of large clones (from several kb to several hundred kb, see Laan et al (1995) Genome Res. 5: 13-20), improvements in sensitivity may allow performance of FISH mapping using shorter probes. A variety of methods based on nucleic acid amplification for genetic and physical mapping can be carried out using nucleic acids. Examples include amplification of specific alleles (Kazazian (1989) J. Lab. Clin. Med 11: 95-96), fragment polymorphism amplified with PCR (CAPS, Sheffield et al. (1993) Genomics 16: 325-332), ligation of specific alleles (Landegren et al. (1988) Science 241: 1077-1080), nucleotide extension reactions (Sokolov (1990) Nucleic Acid Res. 18: 3671), Hybrid Mapping by Radiation (Walter et al. 1997) Nat. Genet 7: 22-28) and Happy Mapping (Dear and Cook (1989) Nucleic Acid Res. 17: 6795-6807). For these methods, the sequence of a nucleic acid is used to design and produce primer pairs for use in the amplification reaction or in primer extension reactions. The design of such primers is well known to those skilled in the art. In methods that use genetic mapping based on PCR, it may be necessary to identify the differences in the DNA sequence between the progenitors of the mapping junction in the region corresponding to the instantaneous nucleic acid sequence. This, however, is generally not necessary for mapping methods. The methods according to the present invention result in plants having an increased yield, as described hereinbefore. The increased performance trait may also be combined with other economically advantageous traits, such as performance enhancing traits, tolerance to various stress conditions, traits that modify various architectural features and / or biochemical and / or physiological characteristics. DESCRIPTION OF THE FIGURES The present invention will now be described with reference to the following figures in which: Fig. 1 shows the structure of the domain typical of the MIKC MADS box transcription factors. The MADS domain is located at the amino-terminal end of the protein and encodes a DNA link and dimerization function. The conserved K domain is involved in protein dimerization. Domains I and C are less well preserved. The C domain can be involved in the transcriptional activation or formation of higher order MADS multimers (from Jack (2001) Plant Molec Biol 46: 515-520). Fig. 2 shows a multiple alignment of several transcription factors of the MADS domain of the SQUAMOSA plant, using the AlignX VNTI multiple alignment program, based on a modified Clustal algorithm (InforMax, Bethesda, MD, http: // www. .informaxinc.com), with default settings for the penalty for opening empty spaces of 10 and an empty space extension of 0.05). The specific SQUAMOSA residues of the MADS domain are presented through the alignment that includes the MADS consensus sequence. The two dicotyledonous subclades within the SQUAMOSA ciat are indicated as the dicotyledonous API and dicotyledonous FUL. Monocotyledon sequences are further subdivided with respect to their conserved motifs at the C-terminal end of the protein, LPPWMLRT and LPPWMLSH presented in bold. Fig. 3 depicts a close, non-root binding hierarchy derived from a sequence alignment using ClustalW 1.83 with default values. The two main groups, comprising monocotyledonous and dicotyledonous proteins, can each be further divided into API and FUL subclades for dicotyledons, and the motifs comprising the C-terrrdnal ends LPPWMLRT (SEQ ID NO: 18) and LPPWMLSH (SEQ ID NO: 19) LPPWMLRT (SEQ ID NO: 18) and LPPWMLSH (SEQ ID NO: 19) for monocotyledons. The source, description and access number of the polypeptide sequences used are given in the following table.

Fig. 4 shows a binary vector p0643, for the expression in Oryza sativa of an Oryza sativa similar to 0sMADS18 (internal reference CDS2787) under the control of a 0SH1 promoter (internal reference PRO0200). Fig. 5 details examples of sequences useful in carrying out the methods according to the present invention. Examples The present invention will now be described with reference to the following examples, which are by way of illustration only. DNA manipulation: unless otherwise stated, recombinant DNA techniques are performed in accordance with the standard protocols described in (Sambrook (2001) Molecular Cloning: a laboratory manual, 3rd Edition Cold Spring Harbor Laboratory Press, CSH, New York) or in Volumes 1 and 2 of Ausubel et al. (1994), Current Protocols in Molecular Biology, Current Protocols. Standard materials and methods for molecular work in plants are described in Plant Molecular Biology Labfase (1993) of R.D.D. Cray, published by BIOS Scientific Publications Ltd (UK) and Blackwell Scientific Publications (UK). Example 1: Genetic Cloning The gene similar to OsMADS18 of Oryza sativa (CDS2787) was amplified by PCR using a cDNA library of Oryza sativa seedlings (Invitrogen, Paisley, UK) as a template. After reverse transcription of the RNA extracted from the seedlings, the cDNAs were cloned into pCMV Sport 6.0. The average insert size of the bank was 1.6 kb and the original number of clones was of the order of 1.67 x 107 cfu. The original titration was determined to be 3.34 x 10 cfu / ml after the first amplification of 6 x 10 10 cfu / ml. After plasmid extraction, 200 ng of the template was used in a 50 μm mixture. of PCR. The primers prm05821 (SEQ ID NO: 20, sense, start codon in bold, AttBl site in italics: 5'- GGGGACAACAAGTTTGTACAAAAAAGCAGGCTTCACAATGGGGAGAGGGCCG 3 ') and prm05822 (SEQ ID NO: 21, inverse, complementary, site AttB2 in italics: 5 ' GGGGACCACTTTGTACAAGAAAGCTGGGTGAGTGGAGTGACGTTGAGA3 '), which includes the AttB sites for Gateway recombination, were used for PCR amplification. PCR was performed using Hifi Taq DNA polymerase under standard conditions. A PCR fragment of 849 bp (including the attB sites) was amplified and purified using standard methods as well. The first step of the Gateway procedure, the BP reaction, was then performed, during which the PCR fragment is recombined in vivo with the plasmid pDONR201 to produce, according to the Gateway terminology, an "entry clone", p05838. Plasmid pDONR201 was purchased from Invitrogen, as part of Gateway® technology. Example 2: Construction of Vector The entry clone p05838 was subsequently used in an LR reaction with p05294, a target vector used for the transformation of Oryza sativa. This vector contains as functional elements within the limits of T-DNA: a selectable marker of plants; a cassette for expression of the selectable marker; and a proposed Gateway cassette for LR recombination in vivo with the sequence of interest already cloned in the entry clone. A rice OSH1 promoter (SEQ ID NO: 22) for the expression of the early apical meristem (PRO0200) was located upstream of this Gateway cassette (Matsuoka et al., Plant Cell 5 1993, 1039-1048). After the LR recombination step, the resulting expression vector p0643 (Figure 4) was transformed into strain LBA4044 of Agrobacteriuw and subsequently to Oryza sativa plants. The transformed rice plants were grown and then examined for the parameters described in Example 3. Example 3: Evaluation and Results of OsMADS18 under the control of rice OSHl promoter Approximately 15 to 20 independent transformants of rice T0 were generated. The primary transformants were transferred from a tissue culture chamber to a greenhouse for the cultivation and harvest of the IT seed. 5 cases were retained, of which the IT progeny segregated 3: 1 for the presence / absence of the transgene. For each of these cases, approximately 10 IT seedlings containing the transgene (hetero- and homozygous) and approximately 10 IT seedlings lacking the transgene (nullizygotes), were selected by monitoring the expression of the visual marker. In addition, 4 IT cases were evaluated in the T2 generation following the same evaluation procedure in terms of the IT generation but with more individuals per case. Statistical analysis: Test F A two-factor ANOVA (variant analysis) was used as a statistical model for the total evaluation of the phenotypic characteristics of the plant. The F test was carried out on all the measured parameters of all plants of all cases transformed with the gene of the present invention. The F test was carried out to verify an effect of the gene on all cases of transformation and for a total effect of the gene, also known as a global gene effect. The threshold of importance for a true effect of the global gene was established at a 5% probability level for the F test. The significant value points of the F test for a gene effect means that not only the presence or position of the gene that causes the differences in the phenotype. Measurements of the parameter related to the seeds The primary panicles, mature, were harvested, placed in bags, labeled with a bar code and then dried for three days in an oven at 37 ° C. The panicles were threshed then and all the seeds were collected and counted. The filled pods were separated from the empty pods using an air insufflation device. The empty pods were discarded and the remaining fraction counted again. The stuffed pods were weighed on an analytical balance. The number of filled seeds was determined by counting the number of filled pods that remained after the separation step. The total yield of the seeds was measured by weighing all the filled pods harvested from a plant. The total number of seeds per plant was measured by counting the number of pods harvested from a plant. The Weight of Thousands of Seeds (TKW) was extrapolated from the number of filled seeds counted and their total weight. The individual parameters of the seed (including width, length, area, weight) were measured using a custom-made device consisting of two main components, a weighing and imaging device, coupled to the computer program for analysis of pictures. The results tables (Tables 5 and 6) below show the p values of the F test for the TI and T2 generations. The percentage difference between the transgenic plants and the corresponding nullicigotes is also shown. The TKW increases significantly in both the TI and T2 generations (Tables 5 and 6). In parallel, an increase in the individual seed area is observed, which contributes to the observed TKW increase. This increase in the seed area is due to a significant increase in the length of the individual seed (Tables 5 and 6), when the width of the individual seed does not change significantly (data not shown).

Table 6: Results of the generation Table 7: Results of generation T2

Claims (27)

1. CLAIMS 1. - Method for increasing the yield in relation to the corresponding wild plants, characterized in that it comprises increasing the activity in a plant, of a polypeptide similar to 0sMADS18 or a homologue thereof, and optionally selecting plants that have an increased yield, in wherein said polypeptide similar to 0sMADS18: (i) is a MADS-box monocotyledonous transcription factor of the SQUAMOSA family; and (ü) has DNA and protein linker activity; and (iii) comprises the LPPWML T motif or portion (SEQ ID NO: 18) in the last 15 amino acids of the C-terminal end of the protein, which allows a substitution of amino acids anywhere in the motif or portion but not in the second and fourth positions of the reason or portion, which are respectively a proline and a tryptophan; and (iv) has at least 65% sequence identity with the 0sMADS18 protein of SEQ. ID. NO: 2.
2. 2. The method according to claim 1, characterized in that said increased activity is carried out by introducing a genetic modification preferably into the locus or location of a gene encoding a polypeptide similar to 0sMADS18 or a homologue thereof.
3. 3. - The method according to claim 2, characterized in that said genetic modification is effected by means of one of: site-directed mutagenesis, homologous recombination, directed evolution, T-DNA activation and TILLING. 4. - The method to increase the yield in relation to the corresponding wild plants, characterized in that it comprises introducing and expressing in a plant a nucleic acid or a variant thereof, which nucleic acid encodes a polypeptide similar to 0sMADS18, which polypeptide similar to 0sMADS18: (i) it is a transcription factor of monocotyledonous type II ADS-box from the SQUAMOSA patient; and (ii) it has DNA and protein linker activity; and (iii) comprises the reason or portion LPPWMLRT (SEQ ID.
4. NO: 18) in the last 15 amino acids of the C-terminal end of the protein, which allows the substitution of amino acids anywhere in the motif or portion but not in the second and fourth positions of the motif or portion, which are respectively a proline and a tryptophan; and (iv) has at least 65% sequence identity with the OsMADS18 protein of SEQ. ID. NO: 2.
5. 5. - The method according to claim 4, characterized in that said variant is a portion of a nucleic acid similar to 0sMADS18 or a sequence capable of hybridizing with a nucleic acid similar to 0sMADS18, which portion or sequence of hybridization or complement thereof encodes a MADS-box type II monocot transcription factor of SQUAMOSA having DNA and protein linker activity and comprising: (i) the LPPWMLRT motif or portion (SEQ ID NO: 18) ) in the last 15 amino acids of the C-terminal end of the protein, which allows a substitution of amino acids anywhere in the motif or portion but not in the second and fourth positions of the motif or portion, which are respectively a proline and a tryptophan; and / or (ii) having at least 65% sequence identity with the OsMADS18 protein of SEQ. ID. NO: 2.
6. 6. - The method according to claim 4 or 5, characterized in that said nucleic acid similar to OsMADS18 or variant thereof is over-expressed in a plant.
7. 7. - The method according to any of claims 4 to 6, characterized in that said nucleic acid similar to OsMADS18 or variant thereof is of plant origin, preferably of a monocotyledonous plant, preferably in addition to the Poaceae family, more preferably the nucleic acid is of Oryza sativa.
8. 8. - The method according to any of claims 4 to 7, characterized in that said variant encodes an ortholog or parologist of a protein 0sMADS18 of SEQ. ID. NO: 2.
9. 9. - The method according to any of claims 4 to 8, characterized in that said nucleic acid similar to 0sMADS18 or variant thereof is operably linked to an apical meristem promoter from early shoots.
10. 10. The method according to claim 9, characterized in that said apical meristem promoter of early buds is a 0SH1 promoter.
11. 11. - The method according to any of claims 1 to 10, characterized in that said increased yield is selected from any one or more of: (i) increased weight of a thousand grains or seeds (TKW); (ii) increased seed size; (iii) increased seed volume; (iv) increased area of seed; (v) increased length of seed; and (vi) increased seed biomass.
12. 12. - The plant obtainable by means of a method according to any of claims 1 to 11.
13. 13. - A construct or construction, characterized in that it comprises: (a) a nucleic acid encoding a polypeptide similar to 0sMADS18 or variant of the same, which polypeptide similar to 0sMADS18: (i) is a transcription factor of monocotyledonous type II ADS-box of the cited SQUAMOSA; and (ii) has DNA and protein binding activity; and (iii) comprises the LPPWMLRT motif or portion (SEQ ID NO: 18) in the last 15 amino acids of the C-terminus of the protein, which allows substitution of amino acids anywhere in the motif or portion but not in the second and fourth positions of the reason or portion, which are respectively a proline and a tryptophan; and (iv) has at least 65% sequence identity with the 0sMADS18 protein of SEQ. ID. NO: 2; and (b) one or more control sequences capable of manipulating the expression of the nucleic acid sequence of (a)]; and optionally (c) a transcription termination sequence.
14. 14. - A construct according to claim 13, characterized in that said control sequence is an apical meristem promoter of early buds.
15. 15. The construct according to claim 14, characterized in that said promoter of apical meristem of early buds is a 0SH1 promoter.
16. 16. - The construct according to claim 15, characterized in that said 0SH1 promoter is as represented by SEQ. ID. NO: 22.
17. 17. The construct according to any of claims 13 to 16, for use in a method according to any of claims 4 to 11.
18. 18. - A plant transformed with a construct in accordance with any of claims 13 to 17.
19. 19. The method for the production of a transgenic plant having improved yield in relation to the corresponding wild plants, characterized in that the method comprises: (a) introducing and expressing in a plant, part of the plant, or plant cell, a nucleic acid encoding a polypeptide similar to 0sMADS18 or variant thereof, which: (i) it is a transcription factor of monocotyledon type II ADS-box of the SQUAMOSA patient; and (ii) has DNA and protein binding activity; and (iii) comprises the MLPT LPP motif or portion (SEQ ID NO: 18) in the last 15 amino acids of the C-terminus of the protein, which allows substitution of amino acids anywhere in the motif or portion but not in the the second and fourth positions of the reason or portion, which are respectively a proline and a tryptophan; and (iv) has at least 65% sequence identity with the OsMADS18 protein of SEQ. ID. NO: 2; (b) cultivate the plant cell under conditions that promote the growth and development of the plant.
20. 20. A transgenic plant characterized in that it has an increased yield resulting from a nucleic acid or a variant thereof, introduced into said plant, which nucleic acid encodes a polypeptide similar to Os ADS18 which: (i) is a MADS-box type II monocotyledono transcription factor from SQUAMOSA; and (ii) it has DNA and protein linker activity; and (iii) comprises the MLPT LPP motif or portion (SEQ ID NO: 18) in the last 15 amino acids of the C-terminal end of the protein, which allows substitution of amino acids anywhere in the motif or portion but not in the second and fourth positions of the reason or portion, which are respectively a proline and a tryptophan; and (iv) has at least 65% sequence identity with the OsMADS18 protein of SEQ. ID. NO: 2.
21. 21. A transgenic plant according to claim 12, 18 or 20, characterized in that said plant is a monocotyledonous plant, such as sugarcane or characterized in that the plant is a cereal, such as rice, corn , wheat, barley, millet, rye, oats or sorghum.
22. 22. - The harvestable parts of a plant according to any of claims 12, 18, 20 or 21.
23. 23. - The harvestable parts according to claim 22, characterized in that said harvestable parts are seeds.
24. 24. - The products derived from a plant according to claim 21 and / or harvestable parts of a plant according to claim 22 or 23.
25. 25. - The use of a nucleic acid / gene similar to 0sMADS18 or variant of the same, or use of a polypeptide similar to OsMADS18 or its counterpart, with improved performance, especially seed yield.
26. 26. - The use according to claim 25, characterized in that said seed yield includes one or more of the following: increased TKW, increased seed size, increased seed volume, increased seed area, increased length of seed and biomass Increased seed
27. 27. - The use of a nucleic acid / gene similar to OsMADS18 or variant thereof, or the use of a polypeptide similar to 0sMADS18 or its homologue, as a molecular marker.