Genome-Wide Fractionation and Identification of WRKY Transcription Factors in Chinese Cabbage (Brassica rapa ssp. pekinensis) Reveals Collinearity and Their Expression Patterns Under Abiotic and Biotic Stresses

The WRKY transcription factor (TF) plays an important role in plant developmental processes and stress responses. However, little is known about the WRKY TF family in Chinese cabbage (Brassica rapa ssp. pekinensis), although its genome has been completely sequenced. In this study, 145 genes of Chinese cabbage were identified that were anchored onto chromosomes 1–10 and further fractionated into three subgenomes. Organization and syntenic analysis indicated genomic distributions and collinear relationships of the BrWRKYs. Simultaneously, the selection pressures and evolutionary divergence of duplicated gene pairs were analyzed using nonsynonymous substitutions (Ka)/synonymous substitutions (Ks). Phylogenetic analyses showed that 145 BrWRKYs were clustered into three large groups and shared typical characters of WRKY TFs. In addition, Illumina RNA-Seq transcriptome of different tissues (i.e., roots, stems, and leaves) revealed tissue-specific and differential expression profiles of the BrWRKYs, and quantitative real-time polymerase chain reaction analysis showed the distinct and corresponsive expression patterns of the BrWRKYs in response to abiotic and biotic stresses in leaves. This study showed that these gene family members might play several roles in plant development, and abiotic and biotic stress responses might benefit from their functional characterization and utilization in the resistance engineering of Chinese cabbage.