CsWRKY57L enhances freezing tolerance through flavonoid accumulation and modulates growth via SWEETs in tea plants

Tea plant (Camellia sinensis (L.) O. Kuntze) is a cold-sensitive leaf-harvesting crop whose growth, yield, and processed tea quality are all inhibited by low temperatures. Therefore, identifying the regulatory genes involved in tea plant growth and freezing tolerance is crucial for genetic improvement. WRKY transcription factors regulate various plant processes, including growth and development, stress responses, and metabolite biosynthesis. However, the molecular network through which WRKY coordinates these pathways in tea plants remains unclear. In this study, we revealed that CsWRKY57L, a cold-inducible WRKY IIc subfamily member, positively regulated freezing tolerance by directly promoting flavonoid accumulation in tea plants. Transient suppression of CsWRKY57L weakened the freezing tolerance of tea plants by reducing flavonoid content and suppressing the C-repeat-binding factor (CBF) - cold-responsive (COR) gene pathway. In contrast, heterologous overexpression of CsWRKY57L in Arabidopsis had the opposite effect. Additionally, overexpression of CsWRKY57L inhibited reproductive development and accelerated senescence in Arabidopsis. Interaction analysis revealed that CsWRKY57L directly binds to the promoters of CsSWEET1a, CsSWEET15, and AtSWEET15, which encode sugar transporters essential for plant reproductive development, and inhibits their transcription. Overall, the study revealed a dual role of CsWRKY57L in promoting freezing tolerance via flavonoid biosynthesis and inhibiting reproductive development by regulating SWEETs expression. This study uncovers a novel mechanism whereby CsWRKY57L coordinately regulates both stress responses and growth in tea plants, providing a molecular basis for breeding low-temperature-tolerant varieties with restricted reproductive development.