A cycloartenol synthase from the steroidal saponin biosynthesis pathway of Paris polyphylla

Linking soil nutrients, microbial community composition, and enzyme activities to saponin content of Paris polyphylla after addition of biochar and organic fertiliser

The application of organic fertilisers and biochar has become widespread in agroforestry ecosystems to enhance the yield and quality of crops and medicinal plants. However, their specific impact on both the yield and quality of Paris polyphylla (P. polyphylla), along with the underlying mechanisms, remains unclear. In this study, we investigated the distinct effects of organic fertiliser (at concentrations of 5% and 10%) and biochar application (at levels of 2% and 4%) on P. polyphylla saponin content. This content is intricately regulated by available soil nutrients, enzyme activities, and microbial community compositions and activities. Our results clearly demonstrated a significant increase in the saponin content, including total saponin, polyphyllin I (PPI), polyphyllin II (PPII), polyphyllin VI (PPVI), and polyphyllin VII (PPVII), in P. polyphylla following the application of both biochar and organic fertiliser. Moreover, in comparison to the control group, the addition of biochar and organic fertiliser led to a considerable rise in the activity of glycosyltransferase enzyme (GTS) and cycloartenol synthase (CAS) in P. polyphylla. Additionally, it increased soil available potassium (AK) and soil organic matter (SOM) concentration, along with the activity of urease, acid phosphatase, and catalase, although biochar amendment resulted in a decrease in nitrate nitrogen (NO3--N) concentration. Crucially, our findings revealed a positive correlation between total saponin content and the activity of CAS in P. polyphylla, soil AK, SOM concentration, and the activities of urease, acid phosphatase, and catalase. Conversely, there was a negative correlation with NO3--N content. Furthermore, the application of organic fertiliser and biochar significantly influenced microbial community structures and specific microbial taxa. Notably, total saponin content exhibited a positive relationship with the relative abundances of Dehalococcoidia, Saccharomycetes, and Agaricomycetes taxa while showing a negative correlation with the abundance of Verrucomicrobiae. In conclusion, the observed increase in saponin content can be attributed to the modulation of specific microbial taxa in soils, as well as alterations in soil nutrients and enzyme activities resulting from the application of biochar and organic fertiliser. This study identifies a potential mechanism for enhancing saponin content in the artificial cultivation of P. polyphylla.

Integrative analysis of metabolome and transcriptome provides new insights into functional components of Lilii Bulbus

Objective

Lilium brownii var. viridulum (LB) and L. lancifolium (LL) are the main sources of medicinal lily (Lilii Bulbus, Baihe in Chinese) in China. However, the functional components of these two species responsible for the treatment efficacy are yet not clear. In order to explore the therapeutic material basis of Lilii Bulbus, we selected L. davidii var. willmottiae (LD) only used for food as the control group to analyze the differences between LD and the other two (LB and LL).

Methods

Metabolome and transcriptome were carried out to investigate the differences of active components in LD vs LB and LD vs LL. Data of metabolome and transcriptome was analysed using various analysis methods, such as principal component analysis (PCA), hierarchical cluster analysis (HCA), and so on. Differentially expressed genes (DEGs) were enriched through KEGG and GO enrichment analysis.

Results

The PCA and HCA of the metabolome indicated the metabolites were clearly separated and varied greatly in LL and LB contrasted with LD. There were 318 significantly differential metabolites (SDMs) in LD vs LB group and 298 SDMs in LD vs LL group. Compared with LD group, the significant up-regulation of steroidal saponins and steroidal alkaloids were detected both in LB and LL groups, especially in LB group. The HCA of transcriptome indicated that there was significant difference in LB vs LD group, while the difference between LL and LD varied slightly. Additionally, 47 540 DEGs in LD vs LB group and 18 958 DEGs in LD vs LL group were identified. Notably, CYP450s involving in the biosynthesis of steroidal saponins and steroidal alkaloids were detected, and comparing with LD, CYP724, CYP710A, and CYP734A1 in LB and CYP90B in LL were all up-regulated.

Conclusion

This study suggested that steroidal saponins and steroidal alkaloids maybe the representative functional components of Lilii Bulbus, which can provide new insights for Lilii Bulbus used in the research and development of classic famous formula.

Arbuscular mycorrhiza and plant growth promoting endophytes facilitates accumulation of saponin under moderate drought stress

Objective

Paris polyphylla var. yunnanensis, one of the important medicinal plant resources in Yunnan, China, usually takes 6-8 years to be harvested. Therefore, it is urgent to find a method that can not only shorten its growth years, but also improve its quality. In this study, we examined the effects of a combination treatment of arbuscular mycorrhizal fungi (AMF) and plant growth-promoting endophytes (PGPE) and drought stress on the accumulation of saponins in it.

Methods

P. polyphylla var. yunnanensis was infected with a mixture of AMF and PGPE under drought stress. The content of saponins, as well as morphological, physiological, and biochemical indicators, were all measured. The UGTs gene related to saponin synthesis was obtained from transcriptome data by homologous comparison, which were used for RT-PCR and phylogenetic analysis.

Results

Regardless of water, AMF treatment could infect the roots of P. polyphylla var. yunnanensis, however double inoculation with AMF and PGPE (AMF + PGPE) would reduce the infection rate of AMF. Plant height, aboveground and underground fresh weight did not differ significantly between the single inoculation AMF and the double inoculation treatment under different water conditions, but the inoculation treatment significantly increased the plant height of P. polyphylla var. yunnanensis compared to the non-inoculation treatment. Single inoculation with AMF considerably increased the net photosynthetic rate, stomatal conductance, and transpiration rate of P. polyphylla var. yunnanensis leaves under various water conditions, but double inoculation with AMF + PGPE greatly increased the intercellular CO2 concentration and chlorophyll fluorescence parameter (Fv/Fm). Under diverse water treatments, single inoculation AMF had the highest proline content, whereas double inoculation AMF + PGPE may greatly improve the amount of abscisic acid (ABA) and indoleacetic acid (IAA) compared to normal water under moderate drought. Double inoculation AMF + PGPE treatment improved the proportion of N, P, and K in the rhizome of P. polyphylla var. yunnanensis under various water conditions. Under moderate drought stress, AMF + PGPE significantly enhanced the contents of P. polyphylla var. yunnanensis saponins I, II, VII, and total saponins as compared to normal water circumstances. Farnesyl diphosphate synthase (FPPS), Geranyl pyrophosphate synthase (GPPS), Cycloartenol synthase (CAS), and Squalene epoxidase (SE1) were the genes that were significantly up-regulated at the same time. The amount of saponins was favorably linked with the expression of CAS, GPPS, and SE1. Saponin VI content and glycosyl transferase (UGT) 010922 gene expression were found to be substantially associated, as was saponin II content and UGT010935 gene expression.

Conclusion

Under moderate drought, AMF + PGPE was more conducive to the increase of hormone content, nutrient absorption, and total saponin content in P. polyphylla var. yunnanensis, and AMF + PGPE could up regulate the expression of key genes and UGTs genes in one or more steroidal saponin synthesis pathways to varying degrees, thereby stimulating the synthesis and accumulation of steroidal saponins in the rhizome of P. polyphylla var. yunnanensis. The combination of AMF and PGPE inoculation, as well as adequate soil drought, reduced the buildup of saponins in P. polyphylla var. yunnanensis and increased its quality.

Differential regulation of key triterpene synthase gene under abiotic stress in Withania somnifera L. Dunal and its co-relation to sterols and withanolides

Withania somnifera (Ashwagandha), is one of the most reputed Indian medicinal plants, having immense pharmacological activities due to the occurrence of withanolides. The withanolides are biosynthesized through triterpenoid biosynthetic pathway with the involvement of WsCAS leading to cyclization of 2, 3 oxidosqualene, which is a key metabolite to further diversify to a myriad of phytochemicals. In contrast to the available reports on the studies of WsCAS in withanolide biosynthesis, its involvement in phytosterol biosynthesis needs investigation. Present work deals with the understanding of role of WsCAS triterpenoid synthase gene in the regulation of biosynthesis of phytosterols & withanolides. Docking studies of WsCAS protein revealed Conserved amino acids, DCATE motif, and QW motif which are involved in efficient substrate binding, structure stabilization, and catalytic activity. Overexpression/silencing of WsCAS leading to increment/decline of phytosterols confers its stringent regulation in phytosterols biosynthesis. Differential regulation of WsCAS on the metabolic flux towards phytosterols and withanolide biosynthesis was observed under abiotic stress conditions. The preferential channelization of 2, 3 oxidosqualene towards withanolides and/or phytosterols occurred under heat/salt stress and cold/water stress, respectively. Stigmasterol and β-sitosterol showed major contribution in high/low temperature and salt stress, and campesterol in water stress management. Overexpression of WsCAS in Arabidopsis thaliana led to the increment in phytosterols in general. Thus, the WsCAS plays important regulatory role in the biosynthetic pathway of phytosterols and withanolides under abiotic stress conditions.

Identification and Functional Characterization of Oxidosqualene Cyclases from Medicinal Plant Hoodia gordonii

Oxidosqualene cyclases (OSCs) are the key enzymes accountable for the cyclization of 2,3-oxidosqualene to varied triterpenoids and phytosterols. Hoodia gordonii (from the family Apocynaceae), a native of the Kalahari deserts of South Africa, Namibia, and Botswana, is being sold as a prevalent herbal supplement for weight loss. The appetite suppressant properties are attributed to P57AS3, an oxypregnane steroidal glycoside. At the molecular level, the enzymes involved in the biosynthesis of triterpenes and phytosterols from H. gordonii have not been previously reported. In the current study, predicted transcripts potentially encoding oxidosqualene cyclases were recognized first by searching publicly available H. gordonii RNA-seq datasets. Two OSC-like sequences were selected for functional analysis. A monofunctional OSC, designated HgOSC1 which encodes lupeol synthase, and HgOSC2, a multifunctional cycloartenol synthase forming cycloartenol and other products, were observed through recombinant enzyme studies. These studies revealed that distinct OSCs exist for triterpene formation in H. gordonii and provided opportunities for the metabolic engineering of specific precursors in producing phytosterols in this plant species.

Transcriptome analysis of three medicinal plants of the genus Polygonatum: identification of genes involved in polysaccharide and steroidal saponins biosynthesis

Polysaccharides and saponins are the main active components of Polygonati Rhizoma. Studying the molecular mechanism of their synthesis pathway is helpful in improving the content of active components at the molecular level. At present, transcriptome analysis of three Polygonatum species (Polygonatum sibiricum Red., Polygonatum cyrtonema Hua, Polygonatum kingianum Coll. et Hemsl.) has been reported, but no comparative study has been found on the transcriptome data of the three species. Transcriptome sequencing was performed on the rhizomes of three Polygonatum species based on high-throughput sequencing technology, and all transcripts were assembled. A total of 168,108 unigenes were generated after the removal of redundancy, of which 121,642 were annotated in seven databases. Through differential analysis and expression analysis of key enzyme genes in the synthesis pathway of three Polygonatum polysaccharides and steroidal saponins, 135 differentially expressed genes encoding 18 enzymes and 128 differentially expressed genes encoding 28 enzymes were identified, respectively. Numerous transcription factors are involved in the carbohydrate synthesis pathway. Quantitative real-time PCR was used to further verify the gene expression level. In this paper, we present a public transcriptome dataset of three medicinal plants of the genus Polygonatum, and analyze the key enzyme genes of polysaccharide and steroidal saponins synthesis pathway, which lays a foundation for improving the active component content of Polygonati Rhizoma by molecular means.

Comparative transcriptome analysis of different tissues of Solanum khasianum reveals candidate genes involved in steroidal glycoalkaloid biosynthesis

Fruits and leaves of Solanum khasianum C. B. Clarke have long been used as a common Chinese herbal medicine. Steroidal glycoalkaloids (SGAs), the main active ingredient in S. khasianum, exhibit various pharmacological effects. However, genes involved in the SGA biosynthetic pathway in S. khasianum have not yet been identified. Genes encoding potential key SGA biosynthesis enzymes were identified through comprehensive RNA sequencing analysis (RNA-seq) of S. khasianum leaves, stems, and fruits. A total of 123,704 unigenes were obtained, of which 109,775 (88.74%) were annotated in seven public databases. Among these, 54 unigenes potentially involved in SGA biosynthesis were identified. Additionally, 23,636 differentially expressed genes were identified by comparing gene expression levels among the fruits, stems, and leaves of S. khasianum. The structural characteristics and phylogenetic relationship of cycloartenol synthase involved in SGA biosynthesis were further analyzed. Solasodine constituent was detected by high-performance liquid chromatography. This is the first study to report the comparative transcriptome analysis of different tissues of S. khasianum that identifies valuable genes potentially involved in SGA biosynthesis in this species.

A novel sterol glycosyltransferase catalyses steroidal sapogenin 3-O glucosylation from Paris polyphylla var. yunnanensis

BACKGROUND

Paris polyphylla var. yunnanensis is an important medicinal plant, and the main active ingredient of the plant is polyphyllin, which is a steroid saponin with pharmacological activities. The central enzyme genes participating in the biosynthesis of polyphyllin are increasingly being uncovered; however, UGTs are rarely illustrated.

METHODS AND RESULTS

In this study, we cloned a new sterol glycosyltransferase from Paris polyphylla var. yunnanensis and identified its catalytic function in vitro. PpUGT6 showed the ability to catalyse the C-3 glycosylation of pennogenin sapogenin of polyphyllin, and PpUGT6 showed catalytic promiscuity towards steroids at the C-17 position of testosterone and methyltestosterone and the triterpene at the C-3 position of glycyrrhetinic acid. Homology modelling of the PpUGT6 protein and virtual molecular docking of PpUGT6 with sugar acceptors and donors were performed, and we predicted the key residues interacting with ligands.

CONCLUSIONS

Here, PpUGT6, a novel sterol glycosyltransferase related to the biosynthesis of polyphyllin from P. polyphylla, was characterized. PpUGT6 catalysed C-3 glycosylation to pennogenin sapogenin of polyphyllin, which is the first glycosylation step of the biosynthetic pathway of polyphyllins. Interestingly, PpUGT6 demonstrated glycodiversification to testosterone and methyltestosterone at C-17 and triterpene of glycyrrhetinic acid at the C-3 position. The virtual molecular docking of PpUGT6 protein with ligands predicted the key residues interacting with them. This work characterized a novel SGT glycosylating pennogenin sapogenin at C-3 of polyphyllin from P. polyphylla and provided a reference for further elucidation of the phytosterol glycosyltransferases in catalytic promiscuity and key residues interacting with substrates.

RNA-Seq analysis reveals the important co-expressed genes associated with polyphyllin biosynthesis during the developmental stages of Paris polyphylla

Background

Plants synthesize metabolites to adapt to a continuously changing environment. Metabolite biosynthesis often occurs in response to the tissue-specific combinatorial developmental cues that are transcriptionally regulated. Polyphyllins are the major bioactive components in Paris species that demonstrate hemostatic, anti-inflammatory and antitumor effects and have considerable market demands. However, the mechanisms underlying polyphyllin biosynthesis and regulation during plant development have not been fully elucidated.

Results

Tissue samples of P. polyphylla var. yunnanensis during the four dominant developmental stages were collected and investigated using high-performance liquid chromatography and RNA sequencing. Polyphyllin concentrations in the different tissues were found to be highly dynamic across developmental stages. Specifically, decreasing trends in polyphyllin concentration were observed in the aerial vegetative tissues, whereas an increasing trend was observed in the rhizomes. Consistent with the aforementioned polyphyllin concentration trends, different patterns of spatiotemporal gene expression in the vegetative tissues were found to be closely related with polyphyllin biosynthesis. Additionally, molecular dissection of the pathway components revealed 137 candidate genes involved in the upstream pathway of polyphyllin backbone biosynthesis. Furthermore, gene co-expression network analysis revealed 74 transcription factor genes and one transporter gene associated with polyphyllin biosynthesis and allocation.

Conclusions

Our findings outline the framework for understanding the biosynthesis and accumulation of polyphyllins during plant development and contribute to future research in elucidating the molecular mechanism underlying polyphyllin regulation and accumulation in P. polyphylla.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-022-08792-2.