Integration of transcriptomics and metabolomics to identify key coumarin biosynthetic genes in Bupleurum chinense

Bupleurum chinense DC. is a perennial herb plant belonging to the Umbelliferae family, genus Bupleurum, that is used as a traditional Chinese medicine. Coumarins are characteristic secondary metabolites of the Apiaceous family, which possess anti-inflammatory, anti-cancer and antiviral activities, among others. Few studies on the coumarin biosynthesis pathways in B. Chinese have been reported. In this study, we identified 89 differentially expressed genes belonging to 7 gene families involved in the synthesis of coumarins in B. chinense, using transcriptome and metabolomic data obtained by high-throughput RNA-sequencing data analysis, and liquid chromatography tandem mass spectrometry. Five coumarin compounds: esculetin (2), fraxetin (4), psoralen (5), parmesan (6) and angelicin (7) were identified through metabolomic analysis. A total of 39 unigenes belonging to five gene families: shikimate O-hydroxycinnamoyltransferase (HCT), caffeic acid ο-methyltransferase (COMT), 4-coumarate: coenzyme A ligase (4CL), feruloyl-CoA 6'-hydroxylase (F6'H) and psoralen synthase (PS), were identified by correlating coumarin content with transcriptional changes. According to correlation network analysis, PS genes (Bc09210, Bc12711), COMT genes (Bc14830, Bc17539, Bc28792, Bc32856) and HCT genes (Bc32814, Bc10245) may be important factors affecting coumarin biosynthesis.