The CsWRKY21-CsDREB17 module regulates bud dormancy and bud break of tea plants

The timing of spring bud break is a key economic trait in tea (Camellia sinensis) production, as early-harvested tea leaves possess substantially higher commercial value. While CsDREB17 has been implicated in the regulation of bud break, the mechanisms underlying its transcriptional control remain largely unresolved. In this study, we identified CsWRKY21 as a upstream transcription factor of CsDREB17 and demonstrated that CsWRKY21 directly binds to the CsDREB17 promoter and activates its transcription, using yeast one-hybrid, electrophoretic mobility shift assays (EMSA), and dual-luciferase reporter assays. Furthermore, both exogenous abscisic acid (ABA) and low temperature were found to upregulate CsWRKY21 expression and enhance its promoter activity, as revealed by qRT-PCR and GUS histochemical staining, respectively. Functional studies in tea plants showed that silencing CsWRKY21 promoted bud break, whereas overexpression of CsWRKY21 in Arabidopsis delayed seed germination, inhibited growth, and increased sensitivity to ABA and cold stress. Collectively, our results reveal that the CsWRKY21-CsDREB17 module plays a crucial role in spring bud dormancy release, providing new insights into the molecular regulation of this important agronomic trait in tea plants.