Salicylic acid regulates phenolic acid biosynthesis via SmNPR1–SmTGA2/SmNPR4 modules in Salvia miltiorrhiza

Phenolic acids are the main active ingredients in Salvia miltiorrhiza, which can be used for the treatment of many diseases, particularly cardiovascular diseases. It is known that salicylic acid (SA) can enhance phenolic acid content, but the molecular mechanism of its regulation is still unclear. Nonexpresser of PR genes 1 (NPR1) plays a positive role in the SA signaling pathway. In this study, we identified a SmNPR1 gene that responds to SA induction and systematically investigated its function. We found that SmNPR1 positively affected phenolic acid biosynthesis. Then, we identified a novel TGA transcription factor, SmTGA2, which interacts with SmNPR1. SmTGA2 positively regulates phenolic acid biosynthesis by directly up-regulating SmCYP98A14 expression. After double-gene transgenic analysis and other biochemical assays, it was found that SmNPR1 and SmTGA2 work synergistically to regulate phenolic acid biosynthesis. In addition, SmNPR4 forms a heterodimer with SmNPR1 to inhibit the function of SmNPR1, and SA can alleviate this effect. Collectively, these findings elucidate the molecular mechanism underlying the regulation of phenolic acid biosynthesis by SmNPR1-SmTGA2/SmNPR4 modules and provide novel insights into the SA signaling pathway regulating plant secondary metabolism.