bHLH transcription factor negatively regulates biosynthesis of phenolic acids and tanshinones in .

Objective: is a valuable herbal medicine with tanshinone and phenolic acid as the main biological active ingredients. The biosynthetic regulation of these bioactive compounds is controlled by a set of transcription factors (TFs). The basic helix-loop-helix (bHLH) transcription factor plays an important role in various physiological and biochemical processes in plants. However, research on bHLH TFs regulating phenolic acid or tanshinone biosynthesis in is limited.

Methods: qRT-PCR was used for gene expression analysis. The subcellular localization of SmbHLH92 was detected by transient transformation into tobacco leaves, and its fluorescence was observed using a confocal laser scanning microscope. The transcriptional activity of SmbHLH92 was confirmed in the yeast strain. RNA interference hairy roots of -RNAi transgenic lines were obtained through mediated genetic transformation. Ultra performance liquid chromatography (UPLC) was used to detect the changes of phenolic acids and tanshinones.

Results: is a bHLH transcription factor that is highly expressed in the root and phloem of . The subcellular localization and transcriptional activity of SmbHLH92 indicated that SmbHLH92 was located in the nucleus and may be a transcription factor. RNA interference (RNAi) of in hairy roots of significantly increased the accumulation of phenolic acid and tanshinone. Quantitative RT-PCR (RT-qPCR) analysis showed the transcription level of genes encoding the key enzymes involved in the phenolic acid and tanshinone biosynthetic pathways was increased in the hairy roots of the -RNAi transgenic line, comparing with the control line.

Conclusion: These data indicate that is a negative regulator involved in the regulation of phenolic acid and tanshinone biosynthesis in .