SmERF6 promotes the expression of terpenoid pathway in Salvia officinalis and improves the production of high value abietane diterpenes, carnosol and carnosic acid

Carnosol (CO) and carnosic acid (CA) are pharmaceutically important diterpenes predominantly produced in members of Lamiaceae, Salvia officinalis, Salvia fruticosa and Rosmarinus officinalis. Nevertheless, availability of these compounds in plant system is very low. With an effort to improve the in planta content of these diterpenes, SmERF6 (Salvia miltiorrhiza Ethylene Responsive Factor 6) transcription factor was expressed in S. officinalis heterologously. SmERF6 is known to bind at the promoter regions of Copalyl diphosphate synthase (CPS) and Kaurene synthase like (KSL) genes and improve ferruginol content, a common precursor for abietane diterpenes in Salvia genus. Transient expression of SmERF6 exhibited the inter-specific activity in promoting differential accumulation of diterpenes in S. officinalis. Overexpression studies showed elevation in the levels of CO (10-folds) and CA (8-folds). Further, in infiltrated leaves levels of ferruginol (50%) and CA derivatives (rosmanol, epirosmanal, methyl carnosic acid) were significantly upregulated along with the other signature terpenes. While, knockdown of homologous ERF6 resulted in drastic reduction of the metabolite content. Finally, stable transgenic lines of S. officinalis developed through in planta Agrobacterium mediated genetic transformation method accumulated higher levels of CO (4-folds) and CA (3-folds) as compared to wild plants. Overall, the present study is the first report on improving the content of pharmaceutically important diterpenes in S. officinalis by overexpressing pathway specific transcription factor. The current results showed convincing evidence for the concept of improving the content of specialized metabolite(s) in medicinal plants by manipulating the expression of key transcription factors.