Phylogenetic analysis and transcriptional profiling of WRKY genes in sunflower (Helianthus annuus L.): Genetic diversity and their responses to different biotic and abiotic stresses

Abstract

WRKY proteins constitute a large family of transcription factors that play important roles in many aspects of physiological processes and adaptation to environmental challenge. Although previous studies have identified and characterized WRKY genes from sunflower (Helianthus annuus L.) expressed sequence tag and genomic databases, the phylogenetic diversity of WRKY repertoires of oil crop species and the responses of sunflower WRKY proteins to various stressors have not been elucidated. In this study, a total of 860 WRKY members from seven oil crop species, namely, sunflower, sesame, castor bean, soybean, canola, Arachis duranensis, and Arachis ipaensis, were subjected to comparative genomic analysis. Genetic diversity within the WRKY family among these oil crop species was revealed through pairwise comparisons of orthologous groups and phylogenetic analysis. Sequence features and phylogenetic analysis revealed that the WRKY genes of oil crop species belong to well-defined groups or subgroups, and different oil plant species exhibit obvious expansion or loss to different degrees. One hundred nineteen sunflower WRKY (HaWRKY) genes were found to be unevenly distributed across each chromosome. Segmental and tandem duplications contributed to the expansion of group II and III WRKY genes in sunflower, respectively. The duplicated genes generally exhibit divergent expression patterns, which may indicate that neofunctionalization or subfunctionalization of these genes tends to occur after duplication. Moreover, expression profiles derived from transcriptomic data exhibited distinct expression patterns of HaWRKY genes in various tissues and in response to different stress treatments, including hormone treatments, salt and drought stress, infection by the fungus Verticillium dahliae, and colonization by the fungus Rhizoglomus irregulare. According to these results, WRKY genes may be involved in the strong adaptability of sunflower to various environments, thereby contributing to the importance of sunflower as a widely cultivated oil resource. This systematic analysis provides a foundation for further functional characterization of WRKY genes among oil crop species for the improvement of stress resistance.