The jasmonate-responsive transcription factor SmbHLH22 acts as a dual enhancer of salvianolic acid and tanshinone biosynthesis in Salvia miltiorrhiza Bunge

Salvia miltiorrhiza Bunge ( S. miltiorrhiza ), a traditional medicinal plant, is renowned for its bioactive compounds, including salvianolic acids and tanshinones. In this study, we characterized SmbHLH22, a jasmonate (JA)-responsive transcription factor, to elucidate its role in regulating the biosynthesis of these metabolites. SmbHLH22 was cloned from S . miltiorrhiza , and its molecular properties—such as nuclear localization and transcriptional activation activity—were confirmed. Overexpression of SmbHLH22 in transgenic hairy roots significantly enhanced the accumulation of salvianolic acid B, rosmarinic acid, and tanshinones, though it suppressed root biomass. Conversely, dominant repression of SmbHLH22 reduced the levels of these metabolites but promoted growth. Transcriptomic profiling identified 10,817 differentially expressed genes (DEGs), encompassing key enzymes involved in the biosynthesis of medicinal compounds and regulators associated with multiple hormones signaling pathways. Using yeast one-hybrid and dual-luciferase assays, we demonstrated that SmbHLH22 binds to G-box elements in the promoters of SmRAS1 , SmDXS2 , and SmGGPPS1 , thereby activating their expression. Notably, SmbHLH22 interacts with the JA repressor SmJAZ4, which suppresses its transcriptional activity toward target genes and integrates it into the JA regulatory network. These findings provide new insights into the transcriptional regulation of secondary metabolism in S . miltiorrhiza and suggest SmbHLH22 as a potential target for metabolic engineering to enhance the production of its medicinal compounds. • SmbHLH22 activates SmRAS1 , SmDXS2 and SmGGPPS1 by binding to G-box cis-elements. • SmbHLH22 positively regulates both salvianolic acid and tanshinone biosynthesis. • The JA‑signaling repressor SmJAZ4 suppresses the transcriptional activity of SmbHLH22 toward its target genes. • SmbHLH22 orchestrates hormone networks and transcriptional programs as a novel metabolic engineering target.