The CsMYB44/73-CsmiR408-CsLAC13 module regulates lignin biosynthesis to enhance drought tolerance in tea plants

Tea plants are susceptible to drought stress, with significant impacts on growth, development, and quality. Lignin plays a critical role in tea plants' drought tolerance, while the underlying molecular mechanisms remain largely unexplored. In this study, we found that CsmiR408 was significantly downregulated under drought stress in tea plants, and its expression trend exhibited a significant negative correlation with changes in lignin content. Overexpression of CsmiR408 significantly reduced lignin levels and compromised drought tolerance in transgenic Arabidopsis and tea plants. Meanwhile, our results showed that CsLAC13, as the target gene of CsmiR408, positively regulated lignin accumulation to enhance drought tolerance in tea plants. In addition, we found that drought stress induced the expression of CsMYB44 and CsMYB73, which bind to MBS1 and MBS2 cis-elements in the CsmiR408 promoter to suppress the expression of CsmiR408. Similarly, overexpression of CsMYB44/73 can increase the drought tolerance of tea plants by facilitating lignin biosynthesis. Furthermore, overexpression of CsMYB44/73 suppressed the expression of genes in the flavonoid biosynthetic pathway, leading to a significant reduction in catechin, which indirectly increased the accumulation of lignin. In conclusion, our study proposes a multilevel regulatory module, CsMYB44/73-CsmiR408-CsLAC13, that enhances the drought tolerance of tea plants by promoting lignin accumulation. These findings provide important insights into the molecular mechanisms of drought stress response in tea plants and offer a theoretical basis for breeding drought tolerance varieties.