Comparative genomics reveals the diversification of triterpenoid biosynthesis and origin of ocotillol-type triterpenes in Panax

Lineage-Specific CYP80 Expansion and Benzylisoquinoline Alkaloid Diversity in Early-Diverging Eudicots

Menispermaceae species, as early-diverging eudicots, can synthesize valuable benzylisoquinoline alkaloids (BIAs) like bisbenzylisoquinoline alkaloids (bisBIAs) and sinomenines with a wide range of structural diversity. However, the evolutionary mechanisms responsible for their chemo-diversity are not well understood. Here, a chromosome-level genome assembly of Menispermum dauricum is presented and demonstrated the occurrence of two whole genome duplication (WGD) events that are shared by Ranunculales and specific to Menispermum, providing a model for understanding chromosomal evolution in early-diverging eudicots. The biosynthetic pathway for diverse BIAs in M. dauricum is reconstructed by analyzing the transcriptome and metabolome. Additionally, five catalytic enzymes - one norcoclaurine synthase (NCS) and four cytochrome P450 monooxygenases (CYP450s) - from M. dauricum are responsible for the formation of the skeleton, hydroxylated modification, and C-O/C-C phenol coupling of BIAs. Notably, a novel leaf-specific MdCYP80G10 enzyme that catalyzes C2'-C4a phenol coupling of (S)-reticuline into sinoacutine, the enantiomer of morphinan compounds, with predictable stereospecificity is discovered. Moreover, it is found that Menispermum-specific CYP80 gene expansion, as well as tissue-specific expression, has driven BIA diversity in Menispermaceae as compared to other Ranunculales species. This study sheds light on WGD occurrences in early-diverging eudicots and the evolution of diverse BIA biosynthesis.

Promiscuous Oxidosqualene Cyclases from Neoalsomitra integrifoliola Catalyzing the Formation of Tetracyclic, Pentacyclic, and Heterocyclic Triterpenes

Six oxidosqualene cyclases (NiOSC1-NiOSC6) from Neoalsomitra integrifoliola were characterized for the biosynthesis of diverse triterpene scaffolds, including tetracyclic and pentacyclic triterpenes from the 2,3-oxidosqualene (1) and oxacyclic triterpenes from the 2,3:22,23-dioxidosqualene (2). NiOSC1 showed high efficiency in the production of naturally rare (20R)-epimers of oxacyclic triterpenes. Mutagenesis results revealed that the NiOSC1-F731G mutant significantly increased the yields of (20R)-epimers compared to the wild type. Homology modeling and molecular docking elucidated the origin of the (20R)-configuration in the epoxide addition step.

Identification of two key UDP-glycosyltransferases responsible for the ocotillol-type ginsenoside majonside-R2 biosynthesis in Panax vietnamensis var. fuscidiscus

MAIN CONCLUSION

Two UDP-glycosyltransferases from Panax vienamensis var. fuscidiscus involved in ocotillol-type ginsenoside MR2 (majonside-R2) biosynthesis were identified. PvfUGT1 and PvfUGT2 sequentially catalyzes 20S,24S-Protopanxatriol Oxide II and 20S,24R-Protopanxatriol Oxide I to pseudoginsenoside RT4/RT5 and RT4/RT5 to 20S, 24S-MR2/20S, 24S-MR2. Ocotilol type saponin MR2 (majonside-R2) is the main active component of Panax vietnamensis var. fuscidiscus (commonly known as 'jinping ginseng') and is well known for its diverse pharmacological activities. The use of MR2 in the pharmaceutical industry currently depends on its extraction from Panax species. Metabolic engineering provides an opportunity to produce high-value MR2 by expressing it in heterologous hosts. However, the metabolic pathways of MR2 remain enigmatic, and the two-step glycosylation involved in MR2 biosynthesis has not been reported. In this study, we used quantitative real-time PCR to investigate the regulation of the entire ginsenoside pathway by MeJA (methyl jasmonate), which facilitated our pathway elucidation. We found six candidate glycosyltransferases by comparing transcriptome analysis and network co-expression analysis. In addition, we identified two UGTs (PvfUGT1 and PvfUGT2) through in vitro enzymatic reactions involved in the biosynthesis of MR2 which were not reported in previous studies. Our results show that PvfUGT1 can transfer UDP-glucose to the C6-OH of 20S, 24S-protopanaxatriol oxide II and 20S, 24R-protopanaxatriol oxide I to form pseudoginsenoside RT4 and pseudoginsenoside RT5, respectively. PvfUGT2 can transfer UDP-xylose to pseudoginsenoside RT4 and pseudoginsenoside RT5 to form 20S, 24S-MR2 and 20S, 24S-MR2. Our study paves the way for elucidating the biosynthesis of MR2 and producing MR2 by synthetic biological methods.

Advances in the biosynthesis and metabolic engineering of rare ginsenosides

Rare ginsenosides are the deglycosylated secondary metabolic derivatives of major ginsenosides, and they are more readily absorbed into the bloodstream and function as active substances. The traditional preparation methods hindered the potential application of these effective components. The continuous elucidation of ginsenoside biosynthesis pathways has rendered the production of rare ginsenosides using synthetic biology techniques effective for their large-scale production. Previously, only the progress in the biosynthesis and biotechnological production of major ginsenosides was highlighted. In this review, we summarized the recent advances in the identification of key enzymes involved in the biosynthetic pathways of rare ginsenosides, especially the glycosyltransferases (GTs). Then the construction of microbial chassis for the production of rare ginsenosides, mainly in Saccharomyces cerevisiae, was presented. In the future, discovery of more GTs and improving their catalytic efficiencies are essential for the metabolic engineering of rare ginsenosides. This review will give more clues and be helpful for the characterization of the biosynthesis and metabolic engineering of rare ginsenosides. KEY POINTS: • The key enzymes involved in the biosynthetic pathways of rare ginsenosides are summarized. • The recent progress in metabolic engineering of rare ginsenosides is presented. • The discovery of glycosyltransferases is essential for the microbial production of rare ginsenosides in the future.