Background: Bupleurum chinense DC. is a widely used traditional Chinese medicinal plant. Saikosaponins are the major bioactive constituents of B. chinense, but relatively little is known about saikosaponin biosynthesis. In the present study, we performed an integrated analysis of metabolic composition and the expressed genes involved in saikosaponin biosynthetic pathways among four organs (the root, flower, stem, and leaf) of B. chinense to discover the genes related to the saikosaponin biosynthetic pathway. Results: Transcript and metabolite profiles were generated through high-throughput RNA-sequencing (RNA-seq) data analysis and liquid chromatography tandem mass spectrometry, respectively. Evaluation of saikosaponin contents and transcriptional changes showed 152 strong correlations (P < 0.05) over 3 compounds and 77 unigenes. These unigenes belonged to eight gene families: the acetoacetyl CoA transferase (AACT) (6), HMG-CoA synthase (HMGS) (2), HMG-CoA reductase (HMGR) (2), mevalonate diphosphate decarboxylase (MVD) (1), 1-deoxy-D-xylulose-5-phosphate synthase (DXS) (3), farnesyl diphosphate synthase (FPPS) (11), β-amyrin synthase (β-AS) (13) and cytochrome P450 enzymes (P450s) (39) families. Conclusions: Our results investigated the diversity of the saikosaponin triterpene biosynthetic pathway in the roots, stems, leaves and flowers of B. chinese by integrated transcriptomic and metabolomic analysis, implying that manipulation of P450s genes such as Bc95697 and Bc35434 might improve saikosaponin biosynthesis. This is a good candidate for the genetic improvement of this important medicinal plant.

Bupleuri Radix (BR) is a traditional Chinese medicinal herb with a history of 2000 years of medicinal use. It is primarily used for heat-clearing, liver-soothing, Yang-ascending and sinking-reversing effects. It has huge clinical value in traditional Chinese medicine (TCM) and ethnomedicine. There are more than 200 species in the genus Bupleurum of the Apiaceae family, but their classification and taxonomy have not been unified and clarified. Numerous active compounds have been isolated and identified from BR, such as saikosaponins, volatile oils, polysaccharides, polyacetylenes, lignans, flavonoids and such like, which possess anti-inflammatory, antioxidant, anti-tumor, anti-cancer, hepatoprotective, immunomodulatory and anti-depressant effects. This review provides an overview of the traditional use, germplasm identification, phytochemistry and pharmacological activities of BR. The current research progress of BR is summarized and the innovation points are highlighted, aiming to provide baseline information and expert references for quality control and rational usage of BR in the post-pandemic era.

Bupleurum falcatum L. is frequently used in traditional herbal medicine in Asia. Saikosaponins (SSs) are the main bioactive ingredients of B. falcatum, but the biosynthetic pathway of SSs is unclear, and the biosynthesis of species-specific phytometabolites is little known. Here we resolved the transcriptome profiles of B. falcatum to identify candidate genes that might be involved in the biosynthesis of SSs. By isoform sequencing (Iso-Seq) analyses of the whole plant, a total of 26.98 Gb of nucleotides were obtained and 124,188 unigenes were identified, and 81,594 unigenes were successfully annotated. A total of 1033 unigenes of 20 families related to the mevalonate (MVA) pathway and methylerythritol phosphate (MEP) pathway of the SS biosynthetic pathway were identified. The WGCNA (weighted gene co-expression network analysis) of these unigenes revealed that only the co-expression module of MEmagenta, which contained 343 unigenes, was highly correlated with the biosynthesis of SSs. Comparing differentially expressed gene analysis and the WGCNA indicated that 130 out of 343 genes of the MEmagenta module exhibited differential expression levels, and genes with the most “hubness” within this module were predicted. Manipulation of these genes might improve the biosynthesis of SSs.

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.