The WRKY gene family plays a very diverse role in plant growth and development. These genes contained an evolutionarily conserved WRKY DNA binding domain, which shows functional diversity and extensive expansion of the gene family. In this study, we conducted a genome-wide comparative analysis to investigate the evolutionary aspects of the WRKY gene family across various plant species and revealed significant expansion and diversification ranging from aquatic green algae to terrestrial plants. Phylogeny reconstruction of WRKY genes was performed using the Maximum Likelihood (ML) method; the genes were grouped into seven different clades and further classified into algae, bryophytes, pteridophytes, dicotyledons, and monocotyledons subgroups. Furthermore, duplication analysis showed that the increase in the number of WRKY genes in higher plant species was primarily due to tandem and segmental duplication under purifying selection. In addition, the selection pressures of different subfamilies of the WRKY gene were investigated using different strategies (classical and Bayesian maximum likelihood methods (Data monkey/PAML)). The average dN/dS for each group are less than one, indicating purifying selection. Our comparative genomic analysis provides the basis for future functional analysis, understanding the role of gene duplication in gene family expansion, and selection pressure analysis.

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