SmbHLH37 Functions Antagonistically With SmMYC2 in Regulating Jasmonate-Mediated Biosynthesis of Phenolic Acids in Salvia miltiorrhiza

Abstract

Jasmonates (JAs) are integral to various defense responses and induce biosynthesis of many secondary metabolites. MYC2, a basic helix-loop-helix (bHLH) transcription factor (TF), acts as a transcriptional activator of JA signaling. MYC2 is repressed by the JASMONATE ZIM-domain (JAZ) proteins in the absence of JA, but de-repressed by the protein complex SCFCOI1 on perception of JA. We previously reported that overexpression of SmMYC2 promotes the production of salvianolic acid B (Sal B) in Salvia miltiorrhiza. However, the responsible molecular mechanism is unclear. Here, we showed that SmMYC2 binds to and activates the promoters of its target genes SmTAT1, SmPAL1, and SmCYP98A14 to activate Sal B accumulations. SmbHLH37, a novel bHLH gene significantly up-regulated by constitutive expression of SmMYC2, was isolated from S. miltiorrhiza for detailed functional characterization. SmbHLH37 forms a homodimer and interacts with SmJAZ3/8. Overexpression of SmbHLH37 substantially decreased yields of Sal B. SmbHLH37 binds to the promoters of its target genes SmTAT1 and SmPAL1 and blocks their expression to suppress the pathway for Sal B biosynthesis. These results indicate that SmbHLH37 negatively regulates JA signaling and functions antagonistically with SmMYC2 in regulating Sal B biosynthesis in S. miltiorrhiza.

The methyl jasmonate-responsive transcription factor SmMYB1 promotes phenolic acid biosynthesis in Salvia miltiorrhiza

“…MYC2 is a central transcriptional regulator of jasmonate signaling 41 . SmMYC2 activates the expression of CYP98A14 to promote phenolic acid accumulation in S. miltiorrhiza 42 , 43 , 56 . To date, the molecular mechanism through which SmMYC2 coregulates phenolic acid biosynthesis together with MYB proteins in S. miltiorrhiza remains unknown.…”

Transcription Factor: A Powerful Tool to Regulate Biosynthesis of Active Ingredients in Salvia miltiorrhiza

“… Zhang et al (2020) overexpressed bHLH3 in S. miltiorrhiza , and contents of caffeic acid (CA), salvianolic acid B (Sal B), and rosmarinic acid (RA) were decreased by 50, 62, and 50%, respectively, compared with the control; in addition, the four tanshinone ingredients, the cryptotanshinone (CT), tanshinone I (T-I), tanshinone II A (T-II A), and dihydrotanshinone I (DT-I) decreased to 3, 14.48, 9, and 38% of the control, respectively. Interestingly, SmbHLH37, another bHLH TF of subfamily R like SmbHLH3, negatively regulates the biosynthesis of phenolic acids due to a dual effect, both by repressive binding to promoters of biosynthetic genes, and by a negative feedback loop on jasmonic acid accumulation ( Du et al, 2018 ). Along with suppressing key enzyme genes of the biosynthetic pathway, SmbHLH37 antagonizes transcription activator SmMYC2 and can interact with SmJAZs.…”

Genome-wide Survey of the bHLH Super Gene Family in Brassica napus

“…ZmPTF1 (S26) respond to drought stress [47,64]. Meanwhile, many MYC2 homologous genes in the S2 subfamily (e.g., Catharanthus roseus CrMYC2 [65] and Salvia miltiorrhiza SmMYC2 [66]) are known to be involved in cellular responses to ABA and JA [20][21][22]. Similarly, members in subfamilies S15 and S26 have been demonstrated to respond to ABA [47,64], while members of the S19 subfamily negatively regulate the BR signaling pathway [67].…”