SmNAC36 promotes the biosynthesis of bioactive compounds and drought tolerance in Salvia miltiorrhiza.

Although drought stress typically suppresses plant growth and reduces crop yields, mild drought stress paradoxically enhances the accumulation of bioactive compounds such as salvianolic acids and tanshinones in the medicinal plant Salvia miltiorrhiza. However, the regulatory mechanisms that underlie this phenomenon remain poorly understood. In this study, we identified the NAC transcription factor (TF) SmNAC36 as a key regulator of bioactive compound synthesis and drought response in S. miltiorrhiza. Overexpression of SmNAC36 enhanced the accumulation of tanshinones and salvianolic acids and increased drought resistance. By contrast, SmNAC36 knockout impaired drought tolerance and markedly reduced the contents of bioactive compounds. Further mechanistic studies revealed that SmNAC36 directly binds to the promoters of SmPAL and Sm4CL in the salvianolic acid biosynthetic pathway and to the promoter of SmDXS in the tanshinone biosynthetic pathway, activating the expression of key enzymes that promote the accumulation of lignin and bioactive compounds. SmNAC36 also interacts with the promoter of SmDREB1C, whose encoded AP2/ERF TF regulates drought tolerance by activating the expression of enzymes such as superoxide dismutase and peroxidase that are responsible for mitigating oxidative stress. Our results reveal a dual mechanism by which SmNAC36 integrates drought stress adaptation with bioactive compound synthesis, providing a potential target for metabolic engineering to improve the quality and stress resilience of S. miltiorrhiza.