Genome-wide Identification of WRKY transcription factor family members in sorghum (Sorghum bicolor(L.) moench)

WRKY transcription factors regulate diverse biological processes in plants, including abiotic and biotic stress responses, and constitute one of the largest transcription factor families in higher plants. Although the past decade has seen significant progress towards identifying and functionally characterizingWRKYgenes in diverse species, little is known about the WRKY family in sorghum (Sorghum bicolor(L.) moench). Here we report the comprehensive identification of 94 putative WRKY transcription factors (SbWRKYs). TheSbWRKYs were divided into three groups (I, II, and III), with those in group II further classified into five subgroups (IIa-IIe), based on their conserved domains and zinc finger motif types. WRKYs from the model plant Arabidopsis (Arabidopsis thaliana) were used for the phylogenetic analysis of allSbWRKYgenes. Motif analysis showed that allSbWRKYs contained either one or two WRKY domains and thatSbWRKYs within the same group had similar motif compositions.SbWRKYgenes were located on all 10 sorghum chromosomes, and some gene clusters and two tandem duplications were detected.SbWRKYgene structure analysis showed that they contained 0-7 introns, with mostSbWRKYgenes consisting of two introns and three exons. Gene ontology (GO) annotation functionally categorized SbWRKYs under cellular components, molecular functions and biological processes. Acis-element analysis showed that allSbWRKYscontain at least one stress response-relatedcis-element. We exploited publicly available microarray datasets to analyze the expression profiles of 78SbWRKYgenes at different growth stages and in different tissues. The induction ofSbWRKYsby different abiotic stresses hinted at their potential involvement in stress responses. qRT-PCR analysis revealed different expression patterns forSbWRKYsduring drought stress. Functionally characterizedWRKYgenes inArabidopsisand other species will provide clues for the functional characterization of putative orthologs in sorghum. Thus, the present study delivers a solid foundation for future functional studies ofSbWRKYgenes and their roles in the response to critical stresses such as drought.