Gibberellin-Induced Transcription Factor SmMYB71 Negatively Regulates Salvianolic Acid Biosynthesis in Salvia miltiorrhiza

<i>Salvia miltiorrhiza</i>, the valuable traditional Chinese medicinal plant, has been used in clinics for thousands of years. The water-soluble salvianolic acid compounds are bioactive substances used in treating many diseases. Gibberellins (GAs) are growth-promoting phytohormones that regulate plant growth and development. Previous studies have demonstrated that GAs can promote salvianolic acid accumulation in <i>S. miltiorrhiza</i>; however, the underlying mechanism requires further investigation. Here, we identified a GA-induced R2R3MYB transcription factor (TF), <i>Sm</i>MYB71, from a transcriptome library of GA-treated <i>S. miltiorrhiza</i>. <i>Sm</i>MYB71 was highly expressed in the root of <i>S. miltiorrhiza</i> and localized to the nucleus. <i>Sm</i>MYB71-knockout hairy roots showed higher salvianolic acid accumulation compared to wild lines. Overexpressing <i>Sm</i>MYB71 in <i>S. miltiorrhiza</i> hairy roots significantly decreased the content of salvianolic acid by downregulating key salvianolic acid biosynthesis enzymes such as <i>Sm</i>RAS and <i>Sm</i>CYP98A14. The GCC box in the promoter of <i>Sm</i>MYB71 can bind with <i>Sm</i>ERF115, suggesting that <i>Sm</i>MYB71 is regulated by <i>Sm</i>ERF115 in salvianolic acid biosynthesis. These findings demonstrate a novel regulatory role of <i>Sm</i>MYB71 in GA-mediated phenolic acid biosynthesis. With the development of CRISPR/Cas9-based genome editing technology, the <i>Sm</i>MYB71 regulation mechanism of salvianolic acid biosynthesis provides a potential target gene for metabolic engineering to increase the quality of <i>S. miltiorrhiza</i>.