Genome-wide analysis of the WRKY transcription factor gene family in Gossypium raimondii and the expression of orthologs in cultivated tetraploid cotton

WRKY proteins are members of a family of transcription factors in higher plants that function in plant responses to various physiological processes. We identified 120 candidate WRKY genes from Gossypium raimondii with corresponding expressed sequence tags in at least one of four cotton species, Gossypium hirsutum, Gossypium barbadense, Gossypium arboreum, and G. raimondii. These WRKY members were anchored on 13 chromosomes in G. raimondii with uneven distribution. Phylogenetic analysis showed that WRKY candidate genes can be classified into three groups, with 20 members in group I, 88 in group II, and 12 in group III. The 88 genes in group II were further classified into five subgroups, groups IIa–e, containing 7, 16, 37, 15, and 13 members, respectively. We characterized diversity in amino acid residues in the WRKY domain and/or other zinc finger motif regions in the WRKY proteins. The expression patterns of WRKY genes revealed their important roles in diverse functions in cotton developmental stages of vegetative and reproductive growth and stress response. Structural and expression analyses show that WRKY proteins are a class of important regulators of growth and development and play key roles in response to stresses in cotton.