SmJRB1 positively regulates the accumulation of phenolic acid in Salvia miltiorrhiza

Phenolic acids rank high among the major active metabolites produced in the Chinese herb, Salvia miltiorrhiza, which has a rapidly escalating medicinal demand. Phenolic acid biosynthesis can be induced by methyl jasmonate (MeJA), although the underlying molecular mechanism remains obscure. A jasmonic acid-responsive basic helix-loop-helix (bHLH) transcriptional factor, SmJRB1, was identified in this study from the MeJA-induced transcriptome library of S. miltiorrhiza. The SmJRB1 is localized in the nuclei illustrated by the transient-transformation of epidermal cells in tobacco leaves. Overexpression of the SmJRB1 significantly promoted the accumulation of phenolic acids and upregulated the genes that encode the principal enzymes such as rosmarinic acid synthase I (RAS1) and cytochrome P450-dependent monooxygenase (CYP98A14), which are known to promote the phenolic acid biosynthetic pathway. Further investigation revealed that SmJRB1 triggered the activation of RAS1 transcription, according to the Dual-Luciferase (Dual-LUC) and yeast one-hybrid (Y1H) assays. Furthermore, yeast two-hybrid (Y2H) and biomolecular fluorescence complementation (BiFC) assays demonstrated that SmJRB1 interacted with the Jasmonate ZIM-domain proteins (JAZ) SmJAZ3 and SmJAZ9, and was most likely responsible for the co-regulation of the biosynthesis of phenolic acids. Overall, these results demonstrate that the SmJRB1 is an activator that enhances the phenolic acid accumulation in S. miltiorrhiza, and the study provides insights into the phenolic acid accumulation-related regulatory mechanisms in S. miltiorrhiza, as well as on the metabolic manipulation of the bioactive substances present.