Identification and expression analysis of group III WRKY transcription factors in cotton

The WRKY proteins constitute a large family of transcription factors in plants containing highly conserved WRKYGQK sequences and zinc-finger-like motifs. To comprehensively study WRKY III genes in cotton, we analyzed the genome sequences of Gossypium hirsutum, G. raimondii and G. arboreum. According to the three genome sequences, 18 group III GhWRKY genes were identified in G. hirsutum, 12 both in G. raimondii and G. arboreum. Phylogenetic and motif analysis showed that proteins with high similarities could be clustered together and had the same motif components. The ratios of non-synonymous (Ka) to synonymous (Ks) of the GhWRKY to GrWRKY or GaWRKY were lower than 1, which indicated that group III WRKY genes in Gossypium species are under purifying selection. Expression analysis revealed that group III GhWRKY genes expressed during fiber development and leaf senescence, and most of them could be induced by salicylic acid (SA), jasmonic acid (JA), ethylene, abscisic acid (ABA), mannitol, and NaCl both in roots and cotyledons. Our study gives a briefly introduction on cotton group III WRKY genes and implicates their potential function in cotton fiber development, leaf senescence and abiotic stresses.