Integrated metabolomics and transcriptomics reveal differences in terpenoids and the molecular basis among the roots of three Bupleurum species.

Background: Radix Bupleuri is a popular traditional Chinese medicinal plant. Its root contains saikosaponin and volatile oil compounds with antipyretic, anti-inflammatory, and hepatoprotective pharmacological effects. However, there are differences in the content and type of main chemical components in the roots of three Bupleurum species: Bupleurum chinense DC. (Bchi), Bupleurum scorzonerifolium Willd. (Bsco), and Bupleurum marginatum var. stenophyllum (Wolff) Shan et Y.Li (Bmar). The molecular mechanism behind these differences is still unclear. The present study used integrated metabolome and transcriptome analyses to uncover the differences in metabolites and expressed genes among the three Bupleurum species.

Results: Metabolomics results revealed that Bmar contained more saikosaponins than Bchi and Bsco. Conversely, Bsco had the highest content of volatile oil monoterpenes but a lower sesquiterpene content than Bchi and Bmar. Transcriptome analysis showed that several genes were highly expressed in Bchi, Bsco, or Bmar, demonstrating the molecular mechanism responsible for the differences in their metabolic components. We combined the metabolomics and transcriptomics data to investigate the relationship between metabolites and genes. The results showed a high correlation between CYP450, UGT, and β-AS genes and 6''-acetyl-saikosaponins A, saikosaponins B1, C, and D. The subcellular localization of the two P450 genes (Bc087391 and Bc036879) in the endoplasmic reticulum suggests that they may be involved in saikosaponin biosynthesis.

Conclusion: We performed an integrated transcriptome and metabolome analysis to investigate the diversity of the terpenoid biosynthetic pathway in three Bupleurum species. The study provides new insights into the molecular basis of the metabolic differences between the three Bupleurum species. It also serves as a theoretical basis for the clinical application and breeding of Bupleurum resources.