Pathway engineering for phenolic acid accumulations in Salvia miltiorrhiza by combinational genetic manipulation

To produce beneficial phenolic acids for medical and commercial purposes, researchers are interested in improving the normally low levels of salvianolic acid B (Sal B) produced by Salvia miltiorrhiza. Here, we present a strategy of combinational genetic manipulation to enrich the precursors available for Sal B biosynthesis. This approach, involving the lignin pathway, requires simultaneous, ectopic expression of an Arabidopsis Production of Anthocyanin Pigment 1 transcription factor (AtPAP1) plus co-suppression of two endogenous, key enzyme genes: cinnamoyl-CoA reductase (SmCCR) and caffeic acid O-methyltransferase (SmCOMT). Compared with the untransformed control, we achieved a greater accumulation of Sal B (up to 3-fold higher) along with a reduced lignin concentration. This high-Sal B phenotype was stable in roots during vegetative growth and was closely correlated with increased antioxidant capacity for the corresponding plant extracts. Although no outward change in phenotype was apparent, we characterized the molecular phenotype through integrated analysis of transcriptome and metabolome profiling. Our results demonstrated the far-reaching consequences of phenolic pathway perturbations on carbohydrate metabolism, respiration, photo-respiration, and stress responses. This report is the first to describe the production of valuable end products through combinational genetic manipulation in S. miltiorrhiza plants. Our strategy will be effective in efforts to metabolically engineer multi-branch pathway(s), such as the phenylpropanoid pathway, in economically significant medicinal plants.