Reivindicaciones

1. An expression cassette comprising at least one polynucleotide comprising a nucleotide sequence selected from the group consisting of: a) a nucleotide sequence that encodes a polypeptide having the amino acid sequence set forth in SEQ ID NOs. 13-24;and b) a nucleic acid sequence that encodes a polypeptide having the amino acid sequence sharing at least 50%, preferably at least 55%, 60%, 65%, 70%, 75%, 80%, 85%, especially preferably at least 90%, 95%, 97%, 98%, 99%, or more of sequence identity with a sequence selected in the group consisting of SEQ ID NOs. 13-24. 2. An expression cassette according to claim 1, wherein said expression cassette has a sequence selected from the sequences represented by SEQ ID NOs. 30-41. 3. A plant cell comprising the expression cassette according to any one of claims 1 or 2. 4. A transgenic plant comprising a plant cell according to claim 3. 5. The transgenic plant of claim 4, wherein said plant is a monocot or a dicot. 6. The transgenic plant of claim 4, wherein said plant is selected from the group consisting of: maize, soybean, sunflower, sorghum, canola, wheat, alfalfa, cotton, rice, barley, millet and sugar cane. 7. A transgenic seed from the transgenic plant of claim 4. 8. A method for the production of a transgenic plant, said method comprising the transformation of a plant by an expression cassette according to any one of claims 1 or 2. 9. A method for increasing or maintaining plant yield under non-optimal conditions for sulphur, nitrogen, and/or C/N balance, said method comprising a step of growing a transgenic plant according to claim 4 under conditions of non- optimal conditions for sulphur, nitrogen, and/or C/N balance, wherein: .cndot. the yield obtained from said transgenic plant grown under said non- optimal conditions is increased as compared to the yield obtained from a plant not containing the expression cassette according to any one of claims 1 or 2, grown under said non-optimal conditions, or .cndot. the yield obtained from said transgenic plants grown under said non- optimal conditions is maintained as compared to the yield obtained from a transgenic 53 plant according to claim 4, and grown in optimal conditions for sulphur, nitrogen, and/or C/N balance 10. A method for increasing or maintaining plant yield under optimal conditions for sulphur, nitrogen, and/or C/N balance, said method comprising a step of growing a transgenic plant according to claim 4 under conditions of optimal conditions for sulphur, nitrogen, and/or C/N balance, wherein the yield obtained from said transgenic plant is increased as compared to the yield obtained from a plant not containing the expression cassette according to any one of claims 1 or 2, grown under said optimal conditions. 11. A method for selecting a plant that can be used in a breeding process for obtaining a plant with improved yield under optimal or under non optimal conditions for sulphur, nitrogen, and/or C/N balance comprising the step of selecting, in a population of plant, the plants containing the recombinant expression cassette according to any one of claims 1 or 2. 12. A method for identifying a plant with improved yield under optimal or under non optimal conditions for sulphur, nitrogen, and/or C/N balance comprising the step of identifying, in a population of plant, the plants containing the recombinant expression cassette according to any one of claims 1 or 2.