CsBPC6 – CsNACX2 – CsTCS1 Module Positively Regulates Caffeine Biosynthesis Under PEG‐Induced Drought Stress in Tea Plants (Camellia sinensis)

Caffeine biosynthesis in tea plants ( Camellia sinensis ) is dynamically regulated by environmental cues; however, the mechanisms linking early drought signals to caffeine accumulation remain unclear. Here, we show that acute PEG‐induced osmotic stress induces rapid caffeine accumulation, accompanied by transcriptional activation of the key biosynthetic gene CsTCS1 . Through integrative analyses, including GWAS and co‐expression network modeling, we identified a CsBPC6 – CsNACX2 – CsTCS1 module as a central regulatory hub. Mechanistically, CsNACX2 directly binds the promoter of the caffeine synthase gene CsTCS1 , activating its transcription and promoting caffeine accumulation. Moreover, the drought‐responsive transcription factor CsBPC6 acts upstream to transactivate CsNACX2 . Functional validation using gene silencing and transient overexpression assays confirmed that the CsBPC6 – CsNACX2 – CsTCS1 module positively regulates caffeine biosynthesis under PEG‐induced drought conditions. Collectively, our findings uncover a previously uncharacterized drought‐responsive transcriptional module governing caffeine biosynthesis, providing new mechanistic insights into how environmental cues regulate secondary metabolism in tea plants.