Extensive intragenic divergences amongst ancient WRKY transcription factor gene family is largely associated with their functional diversity in plants

Abstract

Diversity at gene sequence and function level is an evolutionary outcome of a constantly expanding gene family in plants. Genome sequences have provided a platform to comprehend the evolutionary architecture of genes and gene families, especially in plant genera. Apparently, regulatory sequences and the selection of trans-binding proteins have massive impressions of gene expression evolution as compared with a transformation at genic-level itself. Therefore, it becomes essential to comprehensively dissect the genome-wide structure-function evolution of regulatory regions'-binding trans-proteins. WRKY gene family members are developmentally and functionally diverged ancient transcription factors that notably regulates numerous cellular as well as stress responsive phenotypes in plant species. To comprehend the evolutionary consequences of WRKY genes during plant development, a meta-phylogenetic analyses of at least 266 WRKY amino acid sequences of alga, monocot and eudicots plant species was accomplished. Phylogenetic clustering identified assorted groups and sub-groups of WRKY orthologous or paralogous sequences. Paralogous gene divergences of monocot and eudicot species showed strong ‘purifying’ selection during the sequence evolution. Evidently, evolutionary exon-intron structural diversification predominantly arose by ‘exon/intron-gain’ and insertion/deletion during primeval sequence-exonization. The structural DNA-binding domain, and global structures of WRKY proteins are exceedingly divergent and also explicit to the classified phylogenetic clusters. Expression profiling displayed that Group IIe WRKY members are profusely expressed in root tissues of the representative species. Remarkably, the spatial and temporal gene expression patterns of WRKY genes in plants apprise our perception about their contributions in the regulation of cellular functions; and structural-functionalism of these members speculate their probable employment into future crop improvement programs.