Isolation and expression analysis of 18 CsbZIP genes implicated in abiotic stress responses in the tea plant (Camellia sinensis)

Basic leucine zipper (bZIP) transcription factors (TFs) play essential roles in regulating stress processes in plants. Despite the economic importance of this woody crop, there is little information about bZIP TFs in tea plants. In this study, 18 bZIP genes were isolated from the tea plant (Camellia sinensis) and named sequentially from CsbZIP1 to CsbZIP18. According to the phylogenetic classification as in Arabidopsis, the CsbZIP genes spanned ten subgroups (Group A, B, C, D, E, F, H, I, S and K) of bZIP TFs. When analyzed for organ specific expression, all CsbZIP genes were found to be ubiquitously expressed in roots, stems, leaves and flowers. Expression analysis of CsbZIP genes in response to four abiotic stresses showed that in leaves, 9, 9, 15 and 11 CsbZIPs have 2-fold greater variation in transcript abundance under cold, exogenous ABA, high salinity and dehydration conditions, respectively. In roots, 5, 12, 14 and 11 CsbZIPs were differentially expressed under conditions of cold, exogenous ABA, high salinity and dehydration stresses. Moreover, CsbZIP genes in Groups F, H, S and K exhibited several folds up-and/or down-regulation against the above four stresses. Notably, CsbZIP18 of group K showed significant up-regulation in response to these same stresses, suggesting a vital functional role in stress response. Together, these findings increase our knowledge of bZIP TFs in the tea plant and suggest the significance of CsbZIP genes in plant abiotic responses.