The invention provides an isolated polynucleotide encoding a polypeptide with the sequence of SEQ ID NO: 1 or a variant thereof, wherein the variant is a polypeptide capable of modulating in a plant at least one of: i) biomass, ii) seed yield, and iii) tolerance to at least one environmental stress selected from dought, cold, freezing, heat and salinity. The invention also provides, construct, vectors, host cells, plant cells and plants genetically modified to comprise the polynucleotide. The invention also provides methods for producing and selecting plants that are altered for at least one of: i) biomass, ii) seed yield, and iii) tolerance to at least one environmental stress selected from dought, cold, freezing, heat and salinity, making use of the polynucleotides of the invention.
