ScMYC2 Participates in Methyl Jasmonate-Induced Indole Alkaloid Biosynthesis in Strobilanthes cusia

Indole alkaloids are major bioactive compounds in Strobilanthes cusia. Although methyl jasmonate treatment can promote the accumulation of indole alkaloids in S. cusia, the transcriptional regulation remains unclear. In this study, the jasmonic acid responsive bHLH transcription factor ScMYC2 was cloned and characterized. It encodes a protein containing 477 amino acids, which features typical bHLH-MYC_N and HLH domains. ScMYC2 localized in the nucleus, showed tissue specific expression consistent with indole alkaloid accumulation, and was significantly induced by methyl jasmonate. Furthermore, the coding sequence of ScMYC2 was cloned into an expression vector and overexpressed in Arabidopsis thaliana via Agrobacterium-mediated transformation technology. Alkaloid metabolic analysis was performed on three homozygous A. thaliana lines (ScMYC2-OE1, OE2, OE3) stably transformed using UPLC-MS/MS. The results indicated that, compared with wild-type, 14 differential metabolites were detected in the A. thaliana lines overexpressing ScMYC2. Among them, the content of indole increased to 2.83-fold that of the wild-type, while the indole glycoside component indole-3-cyano-6-O-glucoside increased to 2.35-fold. Yeast two-hybrid screening identified 35 ScMYC2-interacting proteins, including UDP-glycosyltransferase, TOPLESS-related proteins, and E3 ubiquitin-protein ligase. BiFC assays further confirmed the in vivo interaction between ScMYC2 and ScUGT1. These findings suggest that ScMYC2 is associated with methyl jasmonate-responsive regulation of indole alkaloid biosynthesis and provides genetic resources for the cultivation of S. cusia with high medicinal value.