Differential Expression of Genes Involved in Saikosaponin Biosynthesis Between Bupleurum chinense DC. and Bupleurum scorzonerifolium Willd

Development of trisiloxane surfactant vesicles ultrasonic extraction method combined with ultrahigh-performance liquid chromatography tandem mass spectrometry for the rapid differentiation of Bupleuri Radix based on metabolomics

INTRODUCTION

Due to the variety, chemical composition and complex structure, the quality control of Bupleuri Radix (BR) is a challenging task. There are still many trace compounds in BR that are difficult to extract and detect.

OBJECTIVE

To develop an innovative method of trisiloxane surfactant vesicles ultrasonic extraction (TSVUE) combined with ultrahigh-performance liquid chromatography tandem mass spectrometry for the identification from Bupleurum chinense DC. (BC) to Bupleurum scorzonerifolium Willd (BS) based on metabolomics.

METHODS

Based on extraction effect for BR, five different types of surfactants vesicles were prepared and compared. Then, a single-factor test and a response surface methodology study were adopted to obtain the optimal conditions for the surfactant vesicles ultrasonic extraction method. Finally, a non-targeted metabolomics method with information dependent acquisition mode was performed to analyse differential metabolites in BC and BS.

RESULTS

Sugar-based surfactant containing trisiloxane [N-3-propyl-methyltrisiloxane-N-glucoheptonamne (Si(3)N-GHA)] displayed higher extraction efficiency compared to other types of surfactants when it comes to being used in pretreatment methods. And a TSVUE method was established and optimised. In total, 131 constituents were identified in two BR herbs, of which 35 were unreported, and 11 were characterised as chemical markers.

CONCLUSIONS

This method provides promising perspectives for rapidly identifying trace compounds in complex systems of traditional Chinese medicine (TCM), as well as for laying the foundation in the identification of similar herbs from the same species. Meanwhile, these findings serve as a promising application of trisiloxane surfactant vesicles in the extraction field of TCM.

Saikosaponin D exerts cytotoxicity on human endometrial cancer ishikawa cells by inducing apoptosis and inhibiting metastasis through MAPK pathways

Saikosaponin D (SSD) is one of plant secondary metabolic active substance with effective anti-tumor ability; however, the toxicity of Saikosaponin D on human endometrial cancer Ishikawa cells is still unclear. Our results revealed that SSD displayed cytotoxicity on the Ishikawa cell with an IC₅₀ = 15.69 μM, but was non-toxic to the human normal cell line HEK293. SSD could upregulate p21 and Cyclin B to keep cells in the G2/M stage. In addition, it activated the death receptor and mitochondrion routes to induce apoptosis in Ishikawa cells. The transwell chamber and wound healing results showed that SSD inhibited the cell migration and invasion. In addition, we found that it was closely related to the MAPK cascade pathway, and it could mediate the three classical MAPK pathways to block cell metastasis. In conclusion, SSD could be potentially beneficial as a natural secondary metabolite in preventing and treating endometrial carcinoma.

A comprehensive review on traditional and modern research of the genus Bupleurum (Bupleurum L., Apiaceae) in recent 10 years

ETHNOPHARMACOLOGICAL RELEVANCE

The genus Bupleurum (family Apiaceae), comprising approximately 248 accepted species, is widely distributed and used in China, Japan, India, Central Asia, North Africa and some European countries as traditional herbal medicines. Certain species have been reported to have significant therapeutic effects in fever, inflammatory disorders, cancer, gastric ulcer, virus infection and other diseases.

AIM OF THE REVIEW

we performed a comprehensive review of the ten-year research progress in phytochemistry, pharmacology, toxicity, along with bibliometrics research of the genus Bupleurum, aiming to identify knowledge gaps for future research.

MATERIALS AND METHODS

All the literatures are retrieved from library and electronic sources including Web of Science, PubMed, Elsevier, Google Scholar, CNKI and Baidu Scholar. These papers cover studies of the traditional use, phytochemistry, pharmacology, and toxicology of the genus Bupleurum.

RESULTS

There is a long history of using the genus Bupleurum in traditional herbal medicine that dated back to over 2000 years ago. Twenty-five species and 8 varieties with 3 variants within this genus have been reported to be effective to treat fever, pain, liver disease, inflammation, thoracolumbar pain, irregular menstruation and rectal prolapse. The main phytochemicals found in these plants are triterpene saponins, volatile oil, flavonoid, lignans, and polysaccharides. Many of these compounds have also been shown to have anti-inflammatory, anti-tumor, antimicrobial, immunoregulation, neuroregulation, hepatoprotective and antidiabetic activities. Meanwhile, improper usage of Bupleurum may induce cytotoxic effects, and polyacetylenes may be the main poisonous compounds.

CONCLUSIONS

This article summarized recent findings about Bupleurum research from many different aspects. While a small number of Bupleurum species have been investigated through modern pharmacology methods, there are still major knowledge gaps due to inadequate studies and ambiguous findings. Future research could focus on more specific phytochemistry studies combined with mechanistic analysis to provide better guidance to utilize Bupleurum as medicinal resources.

Comparative Transcriptome Analysis Provides Insights into the Molecular Mechanism Underlying the Effect of MeJA Treatment on the Biosynthesis of Saikosaponins in Bupleurum chinense DC

Bupleurum chinense DC. is a well-known traditional Chinese medicinal plant that produces saikosaponins (SSs), which possess hepatoprotective, antipyretic, and anti-inflammatory activities. Methyl jasmonate (MeJA) is a signalling phytohormone that can increase the accumulation of SSs in the root of Bupleurum plants. However, the molecular understanding of MeJA-mediated SS biosynthesis is not clear. Therefore, it is necessary to explore the molecular mechanism underlying the response of B. chinense DC. to MeJA in roots. In this study, we performed comparative transcriptome analysis of B. chinense DC. roots with different MeJA treatment times. In total, 104,057 unigenes were identified, of which 4053 were differentially expressed genes (DEGs). Most of the DEGs were downregulated after MeJA treatment, and GO enrichment analysis showed that they were mainly related to biological processes involved in stress responses and development. A total of 88 DEGs encoding enzymes known to be involved in the SS synthesis pathway were found, and most were significantly downregulated within 24 h. Based on the DEGs, 99 transcription factors (TFs) belonging to the AP2/ERF, WRKY, bZIP, ZFP, and bHLH families with different expression patterns were also identified. Further integrated analysis indicated that 20 DEGs involved in the SS synthesis pathway and 12 DEGs encoding TFs presented strong correlations with the SS contents, and these DEGs may be critical for the biosynthesis and regulation of SSs. These findings will be critical for further study of the response of B. chinense DC. to MeJA for SS biosynthesis.

Auxin induces lateral root formation in Bupleurum: A heme oxygenase dependent approach

Objective

The content of saikosaponins in genus Bupleurum is increased with numbers of lateral root, but the genetic mechanisms are largely unknown. This study aims to identify the heme oxygenase (HO) gene family members of B. chinense and B. scorzonerifolium, and assess their role in the root development in Bupleurum.

Methods

The gene sequences of HO family were selected from iso-seq full-length transcriptome data of B. chinense and B. scorzonerifolium, and were analyzed in physicochemical properties, conserved domains, motifs and phylogenetic relationship. In addition, the expression patterns of HO gene in different parts of roots were compared via transcriptome sequencing and qRT-PCR in the two species.

Results

Five Bupleurum HO genes (BcHO1-BcHO5) belonging to the HO1 subfamily were identified from the transcriptome data, whereas the HO2 subfamily member was not identified. The expression levels of BcHO1 and BcHO2 were significantly higher than those of other three HO members in the transcriptome analysis. In addition, the expression profile of BcHO1 showed consistency with lateral root development in B. chinense and B. scorzonerifolium.

Conclusion

Hos might participate in the auxin-induced morphogenesis of lateral roots. The yield of saikosaponin may be improved by manipulating expression of these genes.

Transcriptome Level Reveals the Triterpenoid Saponin Biosynthesis Pathway of Bupleurum falcatum L

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.

Plant regeneration via callus-mediated organogenesis in commercial variety of Chuanbeichai No. 1 in Bupleurum chinense DC

Bupleurum chinense DC is an important medicinal plant with many active ingredients that are used for the treatment of different types of diseases and valued in pharmaceutical markets. In vitro shoot regeneration can efficiently contribute to the improvement of B. chinense. In the present study, we investigated the effects of the explant type and plant growth regulators (PGRs) on embryogenic callus induction and plant regeneration in B. chinense. Our investigation demonstrated that 2 mg/L 2,4-dichlorophenoxyacetic acid (2,4-D) combined with 1 mg/L thidiazuron (TDZ) played a major role in promoting callus induction from leaf, hypocotyl and stem 2 explants, whereas the most effective treatment for stem 1 callus formation was Murashige and Skoog (MS) medium supplemented with 1 mg/L 2,4-D, 0.5 mg/L 6-benzyladenine (BA) and 0.5 mg/L kinetin (Kin). The highest shoot regeneration rate (57.14%) was obtained from hypocotyl-induced calli in MS medium with 0.5 mg/L Kin after 12 weeks of cultivation. This regeneration protocol can be used in large-scale cultivation and may be useful for future genetic modifications of B. chinense .

Chromosome-Level Genome Assembly of Bupleurum chinense DC Provides Insights Into the Saikosaponin Biosynthesis

Bupleurum chinense DC is a plant widely used in Chinese traditional medicine. Saikosaponins are the major bioactive constituents of B. chinense DC. Saikosaponins biosynthesis in Bupleurum has been more intensively studied than any other metabolic processes or bioactive constituents. However, whole-genome sequencing and chromosome-level assembly for Bupleurum genus have not been reported yet. Here, we report a high-quality chromosome-level genome of B. chinense DC. through the integration of PacBio long-read sequencing, Illumina short-read sequencing, and Hi-C sequencing. The genome was phased into haplotype 0 (621.27 Mb with a contig N50 of 16.86 Mb and a scaffold N50 of 92.25 Mb) and haplotype 1 (600.48 Mb with a contig N50 of 23.90 Mb and a scaffold N50 of 102.68 Mb). A total of 45,909 and 35,805 protein-coding genes were predicted in haplotypes 0 and 1, respectively. The enrichment analyses suggested that the gene families that expanded during the evolution of B. chinense DC are involved in the biosynthesis of isoquinoline alkaloid, tyrosine, and anthocyanin. Furthermore, we analyzed the genes involved in saikosaponin biosynthesis and determined the candidate P450 and UGT genes in the third stage of saikosaponins biosynthetic, which provided new insight into the saikosaponins biosynthetic. The genomic data provide a valuable resource for future investigations of the molecular mechanisms, biological functions, and evolutionary adaptations of B. chinense DC.

Metabolomics Analysis Reveals the Differences Between Bupleurum chinense DC. and Bupleurum scorzonerifolium Willd

Bupleurum chinense DC. and Bupleurum scorzonerifolium Willd. are two varieties of Bupleuri Radix in Chinese Pharmacopoeia 2020. The clinical efficacy of the two bupleurum species is different. The difference in clinical efficacy is closely related to the composition of plant metabolites. In order to analyze the difference in metabolites, we used liquid chromatography coupled with mass spectrometry (LC-MS) for untargeted metabolome and gas chromatography coupled with mass spectrometry (GC-MS) for widely targeted metabolome to detect the roots (R), stems (S), leaves (L), and flowers (F) of two varieties, and detected 1,818 metabolites in 25 classes. We performed a statistical analysis of metabolites. Differential metabolites were screened by fold-change and variable importance in the projection values of the OPLS-DA model, and significant differences were found among different groups. The content of active components (triterpenoid saponins) was found to be high in the BcR group than in the BsR group. Other pharmacological metabolites were significantly different. By Kyoto Encyclopedia of Genes and Genomes annotation and enrichment analysis, we found that differential metabolites of the aboveground parts mainly concentrated in monoterpenoid biosynthesis, while the differential metabolites of the root mainly concentrated in sesquiterpenoid and triterpenoid biosynthesis. Differences in metabolic networks may indirectly affect the metabolic profile of Bc and Bs, leading to differences in clinical efficacy. Our study provides a scientific basis for subsequent biosynthesis pathway and related bioactivity research, and provides a reference for developing non-medicinal parts and guiding the clinical application of Bupleuri Radix.

Transcriptome and metabolome analysis to reveal major genes of saikosaponin biosynthesis in Bupleurum chinense

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.

Analysis of unigenes involved in lateral root development in Bupleurum chinense and B. scorzonerifolium

We identified IAA13 negatively associated with lateral root number by comparing the differential expressed genes between Bupleurum chinense and B. scorzonerifolium. Dried roots of the genus Bupleurum L. are used as a herbal medicine for diseases in Asia. Bupleurum chinense has a greater number of lateral roots than B. scorzonerifolium, but the genetic mechanisms for such differences are largely unknown. We (a) compared the transcriptome profiles of the two species and (b) identified a subset of candidate genes involved in auxin signal transduction and explored their functions in lateral root development. By isoform sequencing (Iso-Seq) analyses of the whole plant, more unigenes were found in B. scorzonerifolium (118,868) than in B. chinense (93,485). Given the overarching role of indole-3-acetic acid (IAA) as one of the major regulators of lateral root development, we identified 539 unigenes associated with auxin signal transduction. Fourteen and 44 unigenes in the pathway were differentially expressed in B. chinense and B. scorzonerifolium, respectively, and 3 unigenes (LAX2, LAX4, and IAA13) were expressed in both species. The number of lateral root primordia increased after exogenous auxin application at 8 h and 12 h in B. scorzonerifolium and B. chinense, respectively. Since overexpression of IAA13 in Arabidopsis reduced the number of lateral roots, we hypothesized that IAA13 is involved in the reduction of the number of lateral roots in B. scorzonerifolium.