Isolated polynucleotides are provided. Each of the isolated polynucleotidescomprise a nucleic acid sequence encoding a polypeptide having an amino acidsequence at least 80 % homologous to SEQ ID NO: 26, 106, 107, 109, 110, 112,114, 115, 118, 119, 122, 123, 124, 126, 95 or 96, wherein the polypeptide iscapable of regulating cotton fiber development. Also provided are methods ofusing such polynucleotides for improving fiber quality and/or yield of a fiberproducing plant, as well as methods of using such polynucleotides forproducing plants having increased biomass/vigor/yield.
