SmJAZ1/8 inhibits the stimulation of SmbHLH59, which limits the accumulation of salvianolic acids and tanshinones in Salvia miltiorrhiza.

Salvia miltiorrhiza is a model medicinal plant that is typically used to treat cardiovascular and cerebrovascular diseases. The primary active medicinal ingredients of S. miltiorrhiza are salvianolic acids and tanshinones. Jasmonate (JA) is a vital phytohormone that regulates secondary metabolism. The exogenous application of methyl jasmonate (MeJA) can promote the accumulation of active ingredients in S. miltiorrhiza. Here, we identified a MeJA-responsive SmbHLH59 gene that encodes for a bHLH IIIe family transcription factor. The overexpression of SmbHLH59 in S. miltiorrhiza increased the contents of salvianolic acids and tanshinones, while the opposite effect was observed when SmbHLH59 was knocked out via CRISPR. Meanwhile, SmbHLH59 was observed to activate the expressions of SmPAL1, SmC4H1, SmHPPR1, SmCPS1, and SmKSL1 genes by binding to the E/G-box elements of their promoters. Further investigations demonstrated that SmJAZ1 and SmJAZ8 interacted with SmbHLH59 to inhibit its activation of these five genes. In summary, a JA signaling pathway component (SmbHLH59) was identified that strongly enhanced the accumulation of salvianolic acids and tanshinones through the direct activation of multiple enzyme genes in their biosynthetic pathways. Consequently, this study enriches our knowledge toward further elucidating the molecular mechanisms behind the regulation of JA in the secondary metabolism of S. miltiorrhiza.