Enhanced production of phenolic acids and tanshinones in hairy roots culture of Salvia miltiorrhiza Bunge by the auxin elicitation

The Salvia miltiorrhiza hairy root culture was established more than 20 years ago and is a potential alternative biotechnological system for the production of bioactive compounds in this herb. However, the contents of phenolic acids and tanshinones in S. miltiorrhiza hairy root culture are relatively lower compared with the naturally grown S. miltiorrhiza plants. Auxin is the first identified phytohormone and involved in biosynthesis of various SMs in plants, whether it could be used as elicitor to increase the yield of target metabolites in S. miltiorrhiza hairy root culture is worthy of investigation. In this study, we treated S. miltiorrhiza hairy roots with different concentration of indole-3-acetic acid (IAA) and the synthetic auxin analog 1-naphthylacetic acid (NAA) to investigate their effects on the growth and secondary metabolite accumulation profiles of S. miltiorrhiza hairy roots. The effects of auxin application on the expression of genes in the biosynthetic pathways of phenolic acids and tanshinones, genes in the auxin signaling pathway, and transcription factor (TF) genes were also analyzed. In addition, the gene co-expression network analysis was performed to screen the genes and TFs that may be involved in the auxin induced phenolic acids and tanshinones accumulation in S. miltiorrhiza hairy roots. Our results provide a reference for efficiently promoting the accumulation bioactive compounds in S. miltiorrhiza hairy roots and shed new light on the molecular mechanisms of regulatory roles of auxin in the secondary metabolism of this species.