AUTHOR=Du Tangzhi , Niu Junfeng , Su Jiao , Li Shasha , Guo Xiaorong , Li Lin , Cao Xiaoyan , Kang Jiefang 

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

JOURNAL=Frontiers in Plant Science

VOLUME=9

YEAR=2018

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2018.01720

DOI=10.3389/fpls.2018.01720

ISSN=1664-462X

ABSTRACT=<p>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 SCF<sup>COI1</sup> on perception of JA. We previously reported that overexpression of <italic>SmMYC2</italic> promotes the production of salvianolic acid B (Sal B) in <italic>Salvia miltiorrhiza.</italic> However, the responsible molecular mechanism is unclear. Here, we showed that SmMYC2 binds to and activates the promoters of its target genes <italic>SmTAT1</italic>, <italic>SmPAL1</italic>, and <italic>SmCYP98A14</italic> to activate Sal B accumulations. <italic>SmbHLH37</italic>, a novel bHLH gene significantly up-regulated by constitutive expression of <italic>SmMYC2</italic>, was isolated from <italic>S. miltiorrhiza</italic> for detailed functional characterization. SmbHLH37 forms a homodimer and interacts with SmJAZ3/8. Overexpression of <italic>SmbHLH37</italic> substantially decreased yields of Sal B. SmbHLH37 binds to the promoters of its target genes <italic>SmTAT1</italic> and <italic>SmPAL1</italic> 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 <italic>S. miltiorrhiza</italic>.</p>