The ethylene response factor SmERF6 co-regulates the transcription of SmCPS1 and SmKSL1 and is involved in tanshinone biosynthesis in Salvia miltiorrhiza hairy roots

The SmERF6, which recognizes the GCC-box of SmCPS1 and SmKSL1 promoter in nucleus, regulates the tanshinone biosynthesis in Salvia miltiorrhiza hairy roots. Tanshinone, an important medicinal ingredient in Salvia miltiorrhiza, is best known for its use in medicine. However, the transcription factor regulation of tanshinone biosynthesis is unclear. Here, we isolated and identified a transcription factor in the ERF family of S. miltiorrhiza, SmERF6, which was screened from an S. miltiorrhiza cDNA library by the promoters of two key tanshinone synthesis genes (SmKSL1 and SmCPS1); this factor regulated tanshinone biosynthesis. The gene was highly expressed in the root and responded to ethylene treatment. SmERF6 modulated tanshinone biosynthesis by directly binding to an ethylene-responsive element (GCC-box) of the SmKSL1 and SmCPS1 promoters and activating their transcription. Overexpression of SmERF6 in the hairy roots increased their tanshinone accumulation, and SmERF6 silencing by RNAi led to a lower tanshinone content. Furthermore, tanshinone accumulation maintained homeostasis with the total phenolic acid and flavonoid contents in S. miltiorrhiza. These findings elucidated how SmERF6 directly co-regulates the transcription of SmCPS1 and SmKSL1 and modulates tanshinone synthesis to accelerate the metabolic flux of tanshinone accumulation in S. miltiorrhiza.