Genome- and Transcriptome-Wide Characterization of bZIP Gene Family Identifies Potential Members Involved in Abiotic Stress Response and Anthocyanin Biosynthesis in Radish (Raphanus sativus L.)

Basic leucine zipper (bZIP) transcription factors play crucial roles in various abiotic stress responses as well as anthocyanin accumulation. Anthocyanins are most abundant in colorful skin radish, which exhibit strong antioxidant activity that offers benefits for human health. Here, a total of 135 bZIP-encoding genes were identified from radish genome. Synteny analysis showed that 104 radish and 63 Arabidopsis bZIP genes were orthologous. Transcriptome analysis revealed that 10 RsbZIP genes exhibited high-expression levels in radish taproot (RPKM>10). Specifically, RsbZIP010 exhibited down-regulated expression under Cd, Cr and Pb stresses, whereas RsbZIP031 and RsbZIP059 showed significant down-regulation under heat and salt stresses, respectively. RT-qPCR analysis indicated that RsbZIP011 and RsbZIP102 were significantly up-regulated in the tissues of radish with high anthocyanin contents. Furthermore, the promoter sequences of 39 anthocyanin-related genes were found to contain G-box or ACE-box elements that could be recognized by bZIP family members. Taken together, several RsbZIPs might be served as critical regulators in radish taproot under Cd, Cr, Pb, heat and salt stresses. RsbZIP011 and RsbZIP102 were the potential participants in anthocyanin biosynthesis pathway of radish. These results facilitate further investigation on functional characterization of bZIP genes in response to abiotic stress and anthocyanin biosynthesis in radish.