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

The biosynthesis of trillin 6'-O-glucoside: A low-abundance yet pharmacologically active polyphyllin from Paris polyphylla

Natural products from medicinal plants serve as an invaluable resource for drug discovery and development. However, low-abundance natural products are often understudied due to the challenges of obtaining sufficient quantities for pharmacological testing in cells or animals. Additionally, their complex stereochemistry and functional groups make chemical synthesis and purification difficult. In this study, we showcased the power of biosynthetic approaches to explore these underexplored compounds, using the low-abundance polyphyllin trillin 6'-O-glucoside from Paris polyphylla as an example. We identified two trillin 6'-O-glucosyltransferases required for its biosynthesis and successfully reconstructed the entire pathway in Nicotiana benthamiana. We demonstrated that trillin 6'-O-glucoside exhibits anti-bacterial activity comparable to major polyphyllins like polyphyllins I, II, and VII. Notably, it also showed much lower hemolytic activity, a common side effect of those major polyphyllins. Together, our study underscores the advantages of employing biosynthetic approaches to explore natural products that exist in low or trace abundances yet possess equally important pharmacological activities.

Genomics of sterols biosynthesis in plants: Current status and future prospects

Sterols produced by bacteria and all eukaryotic organisms are essential for membrane functionality and stability. They play a vital role in growth, development and in abiotic stress tolerance. They are involved in diverse responses to biotic and abiotic stresses that lead to providing resistance against multiple diseases. Additionally, sterols serve as defensive compounds against herbivorous insects and animals. Phytosterols derived from plants, improve human nutrition and health and cure different ailments. The biosynthetic pathways for sterols and triterpenes exhibit similarities until the synthesis of 2,3-oxidosqualene. The complexity of sterol pathways increases during the advanced stages of polycyclic structure synthesis, and remain poorly comprehended in plants. This review explores the various omics techniques used to unveil the functions of genes associated with the phytosterol pathways. The study investigates the biosynthetic gene clusters to clarify the structural arrangements of genes linked to metabolic pathways. Both the upstream and downstream genes associated with these pathways, as well as their evolutionary connections and interrelations within the pathways were brought to the forefront. Moreover, developing strategies to unravel the biosynthesis completely and their multi-layered regulation are crucial to comprehend the global roles that sterols play in plant growth, development, stress tolerance and in imparting defence against pathogens.

UDP-glucosyltransferases from UGT73 family catalyze 3-O-glucosylation of isosteroidal and steroidal alkaloids in Fritillaria unibracteata var. wabuensis

Fritillaria unibracteata var. wabuensis is an important resource plant for the famous traditional Chinese medicine Fritillariae cirrhosae bulbus ("Chuanbeimu" in Chinese). F. cirrhosae bulbus is the dried bulbs of several species from Fritillaria genus, with isosteroidal alkaloids components assumed as the bioactive ingredients. However, the biosynthesis pathway of isosteroidal alkaloids remains elusive. Here, we adopted F. unibracteata var. wabuensis as a material to identify genes involved in the biosynthesis of isosteroidal alkaloids. We first constructed the multi-tissue metabolome and transcriptome dataset of F. unibracteata var. wabuensis. Interestingly, imperialine-3-β-d-glucoside, an isosteroidal glycoalkaloid, was found to be the major tissue-specific accumulated alkaloid. Through phylogenetic and co-expression analysis, we identified two UDP-glucosyltransferases from UGT73 family catalyzing 3-O-glucosylation of isosteroidal and steroidal alkaloids: imperialine 3-O-glucosyltransferase (FuwI3GT) can use both isosteroidal alkaloid imperialine and steroidal alkaloid solanidine as substrates, while solanidine 3-O-glucosyltransferase (FuwS3GT) can only use steroidal alkaloid solanidine as a substrate. We further approved that the W201 residue of FuwI3GT determined its substrate preference of isosteroidal alkaloids. Overall, our results identified enzymes involved in 3-O-glucosylation of isosteroidal and steroidal alkaloids in F. unibracteata var. wabuensis and paved the way to fully elucidate the isosteroidal alkaloid biosynthesis pathway in Fritillaria species.

Identification and characterization of PpUGT91BP1 as a trillin synthase from Paris polyphylla

Polyphyllins are the active ingredients of the medicinal plant Paris polyphylla. The biosynthesis of different types of polyphyllins all requires the catalysis of glycosyltransferases. Even though significant efforts have been made to identify PpUGTs capable of catalyzing the initial glycosylation reaction, the specific glycosyltransferases responsible for the synthesis of trillin have not been reported in P. polyphylla. Here, we identified a new trillin synthase, named PpUGT91BP1, which was highly expressed in the rhizome. Importantly, PpUGT91BP1 could specifically glycosylate diosgenin but not pennogenin. To improve its catalytic efficiency, we introduced random mutations through error-prone PCR and conducted an activity-based screening. Three mutants with significantly enhanced trillin synthase activity were identified. Finally, we successfully reconstituted trillin biosynthesis in Nicotiana benthamiana, achieving a yield of 3.69 mg/g of plant dry weight using the mutant PpUGT91BP1. Taken together, our results deepen the understanding of the PpUGT91 family's role in polyphyllin biosynthesis in P. polyphylla, facilitating rational selection of better P. polyphylla cultivars and guiding future studies in the metabolic engineering of polyphllins.

Dissection of transcriptome and metabolome insights into the polyphyllin biosynthesis in Paris

BACKGROUND

Polyphyllins are significant medicinal compounds found in Paris species, with different polyphyllins fulfilling distinct medicinal roles. Although some genes involved in polyphyllin synthesis have been identified, further exploration of the genes in the polyphyllin synthesis pathway is necessary due to the extensive genome of Paris species. The content and composition of polyphyllins vary among different Paris species, and the variations in specific polyphyllin levels across these plants make them promising candidates for identifying metabolites and genes associated with the biosynthesis of specific polyphyllins.

RESULTS

In this study, we investigate the global metabolic and transcriptomic profiles of three types of Paris polyphylla var. yunnanensis (Franch.) Hand.-Mazz, one Paris fargesii Franch, and one Paris forrestii (Takht.) H. Li. The rhizome of P. polyphylla is rich in polyphyllin I and II, while P. forrestii is abundant in polyphyllin III, and P. fargesii contains high levels of polyphyllin VI, VII and H. The three Paris species exhibit distinct metabolomic and transcriptomic profiles. Through an integrated analysis of metabolic and transcriptomic data, along with a phylogenetic analysis of genes related to polyphyllin synthesis in Paris, we annotated a total of six 2,3-oxidosqualene cyclases (OSCs), 120 cytochrome P450s (CYPs), and 138 UDP glycosyltransferases (UGTs). Phylogenetic tree analysis of the obtained data assisted in refining the candidate gene pool for OSC, CYP, and UGT. Subsequently, we identified 6, 12, and 26 candidate genes for OSC, CYP, and UGT, respectively. Finally, by combining the analyses of metabolic and genetic differences, we identified a total of 17 candidate genes, including 2 CAS, 4 CYP, and 11 UGT.

CONCLUSIONS

P. fargesii and P. forrestii are candidate medicinal plants for the development and application of specific polyphyllins. Transcripts from the UGT91 subfamily in Paris may play dual roles, contributing to both the synthesis of polyphyllin II and the catabolism of polyphyllin V and VI. The homologous genes of PpUGT73CE1 may regulate the synthesis of polyphyllin VI in P. fargesii. This study provides new insights into the investigation of biosynthetic pathways in medicinal plants that lack gene clusters.

Metabolomics and transcriptomics profiling of three Paris species with varied polyphyllin compositions

Most of the species in Paris have important medicinal values in China. Polyphyllins are the key components in Paris, with varying levels and compositions among different species. This study investigated polyphyllin compositions of 206 Paris samples from 16 different producing areas. 9 Paris polyphylla var. yunnanensis, 3 Paris fargesii, and 3 Paris forrestii were selected based on polyphyllin levels and composition for metabolome and transcriptome analysis. A total of 1,243 metabolites were identified among these samples, along with 92.11 Gb of full-length transcriptome data. This study provides potential candidate genes involved in polyphyllins synthesis in Paris, aiming to facilitate the biosynthesis of different polyphyllins.

Efficient and green production of flavone-5-O-glycosides by glycosyltransferases in Escherichia coli

O-Glycosylflavonoids exhibit diverse biological activities but their low content in plants is difficult to extract and isolate, and chemical synthesis steps are cumbersome, which are harmful to the environment. Therefore, the biosynthesis of O-glycosylflavonoids represents a green and sustainable alternative strategy, with glycosyltransferases playing a crucial role in this process. However, there are few studies on flavone 5-O-glycosyltransferases, which limits the synthesis of rare flavone 5-O glycosides by microorganisms. In this study, we characterized a highly regioselectivity flavone 5-O glycosyltransferase from Panicum hallii. Site-directed mutagenesis at residue P141 switches glucosylation to xylosylation. Using a combinatorial strategy of metabolic engineering, we generated a series of Escherichia coli recombinant strains to biocatalyze glycosylation of the typical flavone apigenin. Ultimately, further optimization of transformation conditions, apigenin-5-O-glucoside and apigenin-5-O-xyloside were biosynthesized for the first time so far, and the yields were 1490 mg/L and 1210 mg/L, respectively. This study provides a biotechnological component for the biosynthesis of flavone-5-O-glycosides, and established a green and sustainable approach for the industrial production of high-value O-glycosylflavones by engineering, which lays a foundation for their further development and application in food and pharmaceutical fields.

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.

Recent developments in the enzymatic modifications of steroid scaffolds

Steroids are an important family of bioactive compounds. Steroid drugs are renowned for their multifaceted pharmacological activities and are the second-largest category in the global pharmaceutical market. Recent developments in biocatalysis and biosynthesis have led to the increased use of enzymes to enhance the selectivity, efficiency, and sustainability for diverse modifications of steroids. This review discusses the advancements achieved over the past five years in the enzymatic modifications of steroid scaffolds, focusing on enzymatic hydroxylation, reduction, dehydrogenation, cascade reactions, and other modifications for future research on the synthesis of novel steroid compounds and related drugs, and new therapeutic possibilities.