The ABA-responsive transcription factor <i>SmMYB32</i> positively modulates tanshinone biosynthesis in <i>salvia miltiorrhiza</i>

Abstract Tanshinones are natural products primarily biosynthesized in the root of Salvia miltiorrhiza. Their accumulation can be promoted by abscisic acid (ABA) treatment, however, the underlying regulatory mechanisms remain largely unclear. Here, an ABA-responsive R2R3-MYB transcription factor SmMYB32 was identified from the ABA-induced transcriptome. Overexpression of SmMYB32 significantly increased the tanshinone content in transgenic S. miltiorrhiza hairy roots by upregulating the expression of tanshinone-biosynthesis genes SmCYP76AH3 and SmCYP71D411, whereas RNA interference (RNAi)-mediated silencing of SmMYB32 produced the opposite effect. Further analysis using yeast one-hybrid (Y1H), dual-luciferase reporter, and electrophoretic mobility shift (EMSA) assays demonstrated that SmMYB32 directly activates the transcription of SmCYP76AH3 and SmCYP71D411. Furthermore, SmMYB32 physically interacts with the ABA receptor SmPYL8, and this interaction inhibits the transcriptional activity of SmCYP76AH3 and SmCYP71D411. These findings uncover a novel regulatory mechanism underlying tanshinone biosynthesis and provide new insights for metabolic engineering in S. miltiorrhiza.