Cloning and expression analysis of novel Aux/IAA family genes in Gossypium hirsutum

Members of the Aux/IAA gene family encode proteins that mediate the responses of auxin-regulated gene expression and regulate various aspects of plant morphological development. Here, we provide the first identification and characterization of nine cDNAs encoding the complete open reading frame (ORF) of the Aux/IAA family in cotton. These were designated GhAux1 to GhAux9 ( G ossypium h irsutum Aux/IAA ). The proteins encoded by these nine genes had either whole or partially conserved domains of the Aux/IAA superfamily, with sequence identity ranging from 14% to 69%. A pair of homeologs exists for each Aux/IAA in G. hirsutum acc. TM-1 with high identity both in ORF sequences and amino acid level. Tissue- and organ-specific analysis showed that transcripts of GhAux1 , GhAux2 , and GhAux3 were abundant in vegetative organs, whereas GhAux4 , GhAux5 , GhAux6 , and GhAux7 were preferentially expressed in ovules on the day of anthesis. GhAux8 and GhIAA16 (previously reported) were also preferentially expressed during fiber developmental stages, especially GhAux8 in fiber early elongation stages, and GhIAA16 in fiber initiation and secondary cell wall thickening stage. GhAux9 was specifically expressed in developing fibers. During the fiber initiation stage, except for GhAux 3 and GhAux 6, the expression of the other eight GhAux s in various lintless–fuzzless and linted–fuzzless mutants demonstrated that they were significantly up-regulated compared with linted–fuzzy TM-1.