De Novo Biosynthesis of Oleanane-Type Ginsenosides in Saccharomyces cerevisiae Using Two Types of Glycosyltransferases from Panax ginseng

Biosynthesis of triterpenoids in plants: Pathways, regulation, and biological functions

Plant triterpenoids, a vast and diverse group of natural compounds derived from six isoprene units, exhibit an extensive array of structural diversity and remarkable biological activities. In this review, we update the recent research progress in the catalytic mechanisms underlying triterpene synthesis and summarize the current insights into the biosynthetic pathways and regulatory mechanisms of triterpenoids. We emphasize the biosynthesis of pharmacologically active triterpenoids and the role of triterpenoid synthesis in plant growth, development, defense mechanisms, and plant-microbe interactions. This insight review offers a comprehensive perspective on the applications and future avenues of triterpenoid research.

Insights into functional divergence, catalytic versatility and specificity of small molecule glycosyltransferases

Glycosylation is one of the most fundamental biochemical processes in cells. It plays crucial roles in diversifying plant natural products for structures, bioavailability and bioactivity, and thus, renders the glycosylated compounds valuable as food additives, nutraceuticals and pharmaceuticals. Moreover, glycosylated compounds impact plant growth, development and stress response. Therefore, understanding the biochemical function of the glycosyltransferases (GTs) is crucial to the elucidation of natural product biosynthetic pathways, improving plant traits and development of processes for industrially-important compounds. UDP-dependent glycosyltransferases (UGTs) that belong to the glycosyltransferase family-1 (GT1) and catalyze the transfer of glycosyl moieties from UDP-sugars to various small molecules, are the key players in natural product glycosylation. Recent studies also found the involvement of non-canonical cellulose synthase-like (CesAs) and glycosyl hydrolase (GH) family enzymes in the glycosylation of plant specialized metabolites. Decades of research on GTs provided critical insights into catalytic mechanism, substrate/product specificity and catalytic promiscuity, but biochemical function and physiological roles of GTs in majority of the natural product biosynthetic pathways remain to be understood. It is also important to redefine high-throughput strategies of GT mining to uncover novel biochemical function, considering that GTs are the large superfamily members in plants and other organisms. This review underscores the roles of GTs in small molecule glycosylation, plant development and stress responses, highlighting the catalytic versatility and substrate/product specificity of GTs in shaping plant metabolic diversity, and discusses the emerging strategies for mining of uncharacterized GTs to unravel biochemical and physiological functions and to elucidate natural product biosynthetic pathways.

Biosynthesis of Edible Terpenoids: Hosts and Applications

Microbial foods include microbial biomass, naturally fermented foods, and heterologously synthesized food ingredients derived from microbial fermentation. Terpenoids, using isoprene as the basic structure, possess various skeletons and functional groups. They exhibit diverse physicochemical properties and physiological activities, such as unique flavor, anti-bacterial, anti-oxidant, anti-cancer, and hypolipemic, making them extensively used in the food industry, such as flavor, fragrance, preservatives, dietary supplements, and medicinal health food. Compared to traditional strategies like direct extraction from natural species and chemical synthesis, microbial cell factories for edible terpenoids have higher titers and yields. They can utilize low-cost raw materials and are easily scaling-up, representing a novel green and sustainable production mode. In this review, we briefly introduce the synthetic pathway of terpenoids and the applications of microbial cell factories producing edible terpenoids. Secondly, we highlight several typical and non-typical microbial chassis in edible terpenoid-producing cell factories. In addition, we reviewed the recent advances of representative terpenoid microbial cell factories with a gram-scale titer in food flavor, food preservation, nutritional enhancers, and medicinal health foods. Finally, we predict the future directions of microbial cell factories for edible terpenoids and their commercialization process.

In planta ectopic expression of two subtypes of tomato cellulose synthase-like M genes affects cell wall integrity and supports a role in arabinogalactan and/or rhamnogalacturonan-I biosynthesis

Diversification of the cellulose synthase superfamily of glycosyltransferases has provided plants with the ability to synthesize varied cell wall polysaccharides such as xyloglucan, mannans, and the mixed-linkage glucans of cereals. Surprisingly, some but not all members of the cellulose synthase-like M (CslM) gene family have recently been shown to be involved in the glycosylation of the aglycone core of a range of triterpenoid saponins. However, no cell wall activity has yet been attributed to any of the CslM gene family members. Here, evolution of the CslM gene family in eudicots is explored to better understand the differences between the two metabolically distinct classes of CslMs (CslM1 and CslM2) and the very closely related CslGs. To achieve this, a robust tBLASTn approach was developed to identify CslM1, CslM2, and CslG sequences using diagnostic peptides, suitable for complex genomes using unannotated and short-read datasets. To ascertain whether both CslM1 and CslM2 proteins have cell wall functions, in addition to the 'saponin' role of CslM2, tomato CslM1 and CslM2 genes were ectopically expressed in Arabidopsis thaliana by stable transformation and in the transient Nicotiana benthamiana system. Transformed plants were analysed with immunofluorescence, immunogold transmission electron microscopy, and cell wall polysaccharides were extracted for monosaccharide linkage analysis. Our results support a role for both CslM1 and CslM2 in the biosynthesis of type II arabinogalactan linkages, generating new insight into how the diverse functions of CslMs can coexist and providing clear targets for future research.

Herbal Multiomics Provide Insights into Gene Discovery and Bioproduction of Triterpenoids by Engineered Microbes

Triterpenoids are natural products found in plants that exhibit industrial and agricultural importance. Triterpenoids are typically synthesized through two main pathways: the mevalonate (MVA) and methylerythritol 4-phosphate (MEP) pathways. They then undergo structural diversification with the help of squalene cyclases (OSCs), cytochrome P450 monooxygenases (P450s), UDP glycosyltransferases (UGTs), and acyltransferases (ATs). Advances in multiomics technologies for herbal plants have led to the identification of novel triterpenoid biosynthetic pathways. The application of various analytical techniques facilitates the qualitative and quantitative analysis of triterpenoids. Progress in synthetic biology and metabolic engineering has also facilitated the heterologous production of triterpenoids in microorganisms, such as Escherichia coli and Saccharomyces cerevisiae. This review summarizes recent advances in biotechnological approaches aimed at elucidating the complex pathway of triterpenoid biosynthesis. It also discusses the metabolic engineering strategies employed to increase the level of triterpenoid production in chassis cells.

Desorption Electrospray Ionization-Mass Spectrometry Imaging-Based Spatial Metabolomics for Visualizing and Comparing Ginsenosides and Lipids among Multiple Parts and Positions of the Panax ginseng Root

Ginsenosides and lipids are both bioactive ingredients for ginseng. Targeting these two categories of components, this study was designed to develop desorption electrospray ionization-mass spectrometry imaging approaches and spatial metabolomics strategies, achieving the visualization and differentiation among different parts of Panax ginseng root (e.g., rhizome, main root, lateral root, fibrous root, and adventitious root). Potential chemical markers were identified by searching an in-house ginsenoside library and online Lipid Maps database, together with high-resolution MS2 data analysis. Six ginsenosides and 11 lipids were diagnostic to differentiate five different parts of the P. ginseng root. Additionally, three ginsenosides and 20 lipids were identified as differential markers among the six positions of the main root of P. ginseng. High-abundance malonyl- and oleanolic acid-ginsenosides were observed in the rhizome. These results assist in understanding the accumulation of bioactive molecules all through the root of P. ginseng, which can benefit its quality control and rational use.

Polygala japonica Houtt.: A comprehensive review on its botany, traditional uses, phytochemistry, pharmacology, and pharmacokinetics

Polygala japonica Houtt. (P. japonica), a member of the Polygala genus in the Polygalaceae family, has been historically utilized in traditional folk medicine as an expectorant, anti-inflammatory, anti-bacterial, and anti-depressant agent. This paper systematically reviews the latest research in botany, traditional uses, phytochemistry, pharmacology, and pharmacokinetics, aiming to provide a scientific foundation for the future development and application of P. japonica and to explore its potential value comprehensively. Approximately 86 compounds have been isolated from P. japonica, with triterpenoid saponins being the most prevalent and bioactive components. Extensive pharmacological activities of P. japonica extracts or compounds have been confirmed in vivo and in vitro, including anti-inflammatory, anti-depressant, neuroprotective, anti-obesity, anti-apoptotic, and skin-protective effects. Additionally, P. japonica has demonstrated significant curative effects and relatively clear pharmacological mechanisms in treating inflammatory and nervous system diseases. Specific components of its primary triterpenoid saponins are rapidly absorbed in the body. This review advocates for deeper scientific research on P. japonica, noting that most current research remains in its early stages and many reported biological activities require further clinical validation. Despite this, the traditional medical use of P. japonica across various cultures attests to its broad application value. Presently, the pharmacological activities of P. japonica extracts and compounds provide a scientific basis for its traditional uses. Future research must ensure the safety and effectiveness of P. japonica through in-depth pharmacokinetic studies, and the establishment of a refined and standardized quality evaluation system is essential for its clinical development and application.

Cultivation optimization promotes ginsenoside and universal triterpenoid production by engineered yeast

Ginseng, a cornerstone of traditional herbal medicine in Asia, garnered significant attention for its therapeutic potential. Central to its pharmacological effects are ginsenosides, the primary active metabolites, many of which fall within the dammarane-type and share protopanaxadiol as a common precursor. Challenges in extracting protopanaxadiol and ginsenosides from ginseng arise due to their low concentrations in the roots. Emerging solutions involve leveraging microbial cell factories employing genetically engineered yeasts. Here, we optimized the fermentation conditions via the Design of Experiment, realizing 1.2 g/L protopanaxadiol in simple shake flask cultivations. Extrapolating the optimized setup to complex ginsenosides, like compound K, achieved 7.3-fold (0.22 g/L) titer improvements. Our adaptable fermentation conditions enable the production of high-value products, such as sustainable triterpenoids synthesis. Through synthetic biology, microbial engineering, and formulation studies, we pave the way for a scalable and sustainable production of bioactive compounds from ginseng.

A Novel Biosynthetic Strategy for Ginsenoside Ro: Construction of a Metabolically Engineered Saccharomyces cerevisiae Strain Using a Newly Identified UGAT Gene from Panax ginseng as the Key Enzyme Gene and Optimization of Fermentation Conditions

Ginsenoside Ro, as one of the few oleanane-type ginsenosides, is well known for its unique molecular structure and biological activities. Currently, research on the biosynthesis of ginsenoside Ro is still in its early stages. Therefore, the establishment of a new ginsenoside Ro cell factory is of great significance for the in-depth development and utilization of genes related to ginsenoside Ro synthesis, as well as for the exploration of pathways to obtain ginsenoside Ro. In this study, we cloned endogenous constitutive promoters, terminators, and other genetic elements from S. cerevisiae BY4741. These elements were then sequentially assembled with the uridine diphosphate glucuronic acid transferase gene identified in our previously study (PgUGAT252645) and several other reported key enzyme genes, to construct DNA fragments used for integration into the genome of S. cerevisiae BY4741. By sequentially transferring these DNA fragments into chemically competent cells of engineering strains and conducting screening and target product detection, we successfully constructed an engineered S. cerevisiae strain (BY-Ro) for ginsenoside Ro biosynthesis using S. cerevisiae BY4741 as the host cell. Strain BY-Ro produced 253.32 μg/L of ginsenoside Ro under optimal fermentation conditions. According to subsequent measurements and calculations, this equates to 0.033 mg/g DCW, corresponding to approximately 31% of the ginsenoside Ro content found in plant samples. This study not only included a deeper investigation into the function of PgUGAT252645 but also provides a novel engineering platform for ginsenoside Ro biosynthesis.

Calenduloside E Ameliorates Inflammatory Responses in Adipose Tissue via Sirtuin 2-NLRP3 Inflammasome Axis

Obesity-related metabolic diseases are associated with a chronic inflammatory state. Calenduloside E (CE) is a triterpene saponin from sugar beet. In mouse models, CE reduced pro-inflammatory cytokines in white adipose tissue (WAT) and decreased macrophage infiltration of WAT. And CE inhibited pyroptosis in J774A.1 cells and WAT by inhibiting the activation of the nucleotide-binding oligomerization domain, leucine-rich repeat and pyrin domain-containing 3 (NLRP3) inflammasome. Moreover, CE could trigger the activation of Sirtuin 2 (SIRT2), leading to a decrease in the acetylation of NLRP3, particularly at the K24 site. In addition, it has been shown that CE can reduce inflammation in adipocytes that have been induced by macrophage-conditioned medium. However, the selective SIRT2 inhibitor AGK2 hindered the beneficial effects of CE. In summary, CE has the capacity to impede NLRP3-mediated pyroptosis by triggering SIRT2 activity, thus positioning CE as a promising therapeutic avenue for combating obesity-related metabolic disorders.

Progress in Identification of UDP-Glycosyltransferases for Ginsenoside Biosynthesis

Ginsenosides, the primary pharmacologically active constituents of the Panax genus, have demonstrated a variety of medicinal properties, including anticardiovascular disease, cytotoxic, antiaging, and antidiabetes effects. However, the low concentration of ginsenosides in plants and the challenges associated with their extraction impede the advancement and application of ginsenosides. Heterologous biosynthesis represents a promising strategy for the targeted production of these natural active compounds. As representative triterpenoids, the biosynthetic pathway of the aglycone skeletons of ginsenosides has been successfully decoded. While the sugar moiety is vital for the structural diversity and pharmacological activity of ginsenosides, the mining of uridine diphosphate-dependent glycosyltransferases (UGTs) involved in ginsenoside biosynthesis has attracted a lot of attention and made great progress in recent years. In this paper, we summarize the identification and functional study of UGTs responsible for ginsenoside synthesis in both plants, such as Panax ginseng and Gynostemma pentaphyllum, and microorganisms including Bacillus subtilis and Saccharomyces cerevisiae. The UGT-related microbial cell factories for large-scale ginsenoside production are also mentioned. Additionally, we delve into strategies for UGT mining, particularly potential rapid screening or identification methods, providing insights and prospects. This review provides insights into the study of other unknown glycosyltransferases as candidate genetic elements for the heterologous biosynthesis of rare ginsenosides.

Transcriptome-Wide Identification and Integrated Analysis of a UGT Gene Involved in Ginsenoside Ro Biosynthesis in Panax ginseng

Panax ginseng as a traditional medicinal plant with a long history of medicinal use. Ginsenoside Ro is the only oleanane-type ginsenoside in ginseng, and has various pharmacological activities, including anti-inflammatory, detoxification, and antithrombotic activities. UDP-dependent glycosyltransferase (UGT) plays a key role in the synthesis of ginsenoside, and the excavation of UGT genes involved in the biosynthesis of ginsenoside Ro has great significance in enriching ginsenoside genetic resources and further revealing the synthesis mechanism of ginsenoside. In this work, ginsenoside-Ro-synthesis-related genes were mined using the P. ginseng reference-free transcriptome database. Fourteen hub transcripts were identified by differential expression analysis and weighted gene co-expression network analysis. Phylogenetic and synteny block analyses of PgUGAT252645, a UGT transcript among the hub transcripts, showed that PgUGAT252645 belonged to the UGT73 subfamily and was relatively conserved in ginseng plants. Functional analysis showed that PgUGAT252645 encodes a glucuronosyltransferase that catalyzes the glucuronide modification of the C3 position of oleanolic acid using uridine diphosphate glucuronide as the substrate. Furthermore, the mutation at 622 bp of its open reading frame resulted in amino acid substitutions that may significantly affect the catalytic activity of the enzyme, and, as a consequence, affect the biosynthesis of ginsenoside Ro. Results of the in vitro enzyme activity assay of the heterologous expression product in E. coli of PgUGAT252645 verified the above analyses. The function of PgUGAT252645 was further verified by the result that its overexpression in ginseng adventitious roots significantly increased the content of ginsenoside Ro. The present work identified a new UGT gene involved in the biosynthesis of ginsenoside Ro, which not only enriches the functional genes in the ginsenoside synthesis pathway, but also provides the technical basis and theoretical basis for the in-depth excavation of ginsenoside-synthesis-related genes.

Recent advances in triterpenoid pathway elucidation and engineering

Triterpenoids are among the most assorted class of specialized metabolites found in all the taxa of living organisms. Triterpenoids are the leading active ingredients sourced from plant species and are utilized in pharmaceutical and cosmetic industries. The triterpenoid precursor 2,3-oxidosqualene, which is biosynthesized via the mevalonate (MVA) pathway is structurally diversified by the oxidosqualene cyclases (OSCs) and other scaffold-decorating enzymes such as cytochrome P450 monooxygenases (P450s), UDP-glycosyltransferases (UGTs) and acyltransferases (ATs). A majority of the bioactive triterpenoids are harvested from the native hosts using the traditional methods of extraction and occasionally semi-synthesized. These methods of supply are time-consuming and do not often align with sustainability goals. Recent advancements in metabolic engineering and synthetic biology have shown prospects for the green routes of triterpenoid pathway reconstruction in heterologous hosts such as Escherichia coli, Saccharomyces cerevisiae and Nicotiana benthamiana, which appear to be quite promising and might lead to the development of alternative source of triterpenoids. The present review describes the biotechnological strategies used to elucidate complex biosynthetic pathways and to understand their regulation and also discusses how the advances in triterpenoid pathway engineering might aid in the scale-up of triterpenoid production in engineered hosts.

Natural products of pentacyclic triterpenoids: from discovery to heterologous biosynthesis

Covering: up to 2022Pentacyclic triterpenoids are important natural bioactive substances that are widely present in plants and fungi. They have significant medicinal efficacy, play an important role in reducing blood glucose and protecting the liver, and have anti-inflammatory, anti-oxidation, anti-fatigue, anti-viral, and anti-cancer activities. Pentacyclic triterpenoids are derived from the isoprenoid biosynthetic pathway, which generates common precursors of triterpenes and steroids, followed by cyclization with oxidosqualene cyclases (OSCs) and decoration via cytochrome P450 monooxygenases (CYP450s) and glycosyltransferases (GTs). Many biosynthetic pathways of triterpenoid saponins have been elucidated by studying their metabolic regulation network through the use of multiomics and identifying their functional genes. Unfortunately, natural resources of pentacyclic triterpenoids are limited due to their low content in plant tissues and the long growth cycle of plants. Based on the understanding of their biosynthetic pathway and transcriptional regulation, plant bioreactors and microbial cell factories are emerging as alternative means for the synthesis of desired triterpenoid saponins. The rapid development of synthetic biology, metabolic engineering, and fermentation technology has broadened channels for the accumulation of pentacyclic triterpenoid saponins. In this review, we summarize the classification, distribution, structural characteristics, and bioactivity of pentacyclic triterpenoids. We further discuss the biosynthetic pathways of pentacyclic triterpenoids and involved transcriptional regulation. Moreover, the recent progress and characteristics of heterologous biosynthesis in plants and microbial cell factories are discussed comparatively. Finally, we propose potential strategies to improve the accumulation of triterpenoid saponins, thereby providing a guide for their future biomanufacturing.

Ginsenosides on stem cells fate specification-a novel perspective

Recent studies have demonstrated that stem cells have attracted much attention due to their special abilities of proliferation, differentiation and self-renewal, and are of great significance in regenerative medicine and anti-aging research. Hence, finding natural medicines that intervene the fate specification of stem cells has become a priority. Ginsenosides, the key components of natural botanical ginseng, have been extensively studied for versatile effects, such as regulating stem cells function and resisting aging. This review aims to summarize recent progression regarding the impact of ginsenosides on the behavior of adult stem cells, particularly from the perspective of proliferation, differentiation and self-renewal.

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.

Regulation of Ethanol Assimilation for Efficient Accumulation of Squalene in Saccharomyces cerevisiae

Squalene is a triterpene that can be obtained from fish and plant oils. It is important in cosmetics and vaccines and is a precursor for many high-value terpenes and steroids. In order to increase squalene accumulation, the mevalonate pathway was systematically enhanced. Accumulation of squalene tended to increase when ethanol was added as a carbon source during fermentation, but a high concentration of ethanol affected both the strain growth and accumulation of products. By overexpressing the key trehalose synthesis gene TPS1 and the heat shock protein gene HSP104, the content of trehalose by Saccharomyces cerevisiae (S. cerevisiae) was enhanced, and stress caused by ethanol was relieved. The OD₆₀₀ value of the modified S. cerevisiae strain was increased by 80.2%, its ethanol tolerance was increased to 30 g/L, and it retained excellent activity with 50 g/L ethanol. After optimizing the fermentation conditions, the squalene titer in a 5 L bioreactor reached 27.3 g/L and the squalene content was 650 mg/g dry cell weight, the highest squalene production parameters reported to date for a microorganism.

Genome-wide analysis of Panax MADS-box genes reveals role of PgMADS41 and PgMADS44 in modulation of root development and ginsenoside synthesis

Panax root is an important material used in food and medicine. Its cultivation and production usually depend on root shape and ginsenoside content. There is limited understanding about the synergistic regulatory mechanisms underlying root development and ginsenoside accumulation in Panax. MADS-box transcription factors possibly play a significant role in regulation of root growth and secondary metabolites. In this study, we identified MADS-box transcription factors of Panax, and found high expression levels of SVP, ANR1 and SOC1-like clade genes in its roots. We confirmed that two SOC1-like genes, PgMADS41 and PgMADS44, bind to expansion gene promoters (PgEXLB5 and PgEXPA13), which contribute to root growth, and to SE-4, CYP716A52v2-4, and β-AS-13 promoters, which participate in ginsenoside Ro biosynthesis. These two genes were found to increase lateral root number and main root length in transgenic Arabidopsis thaliana by improving AtEXLA1, AtEXLA3, AtEXPA5, and AtEXPA6 gene expression. As a non-phytohormone regulatory tool, Ro can stimulate adventitious root growth by influencing their expression and ginsenoside accumulation. Our study provides new insights into the coordinated regulatory function of SOC1-like clade genes in Panax root development and triterpenoid accumulation, paving the way towards understanding root formation and genetic improvement in Panax.

Deciphering the network of cholesterol biosynthesis in Paris polyphylla laid a base for efficient diosgenin production in plant chassis

Cholesterol serves as a key precursor for many high-value chemicals such as plant-derived steroidal saponins and steroidal alkaloids, but a plant chassis for effective biosynthesis of high levels of cholesterol has not been established. Plant chassis have significant advantages over microbial chassis in terms of membrane protein expression, precursor supply, product tolerance, and regionalization synthesis. Here, using Agrobacterium tumefaciens-mediated transient expression technology, Nicotiana benthamiana, and a step-by-step screening approach, we identified nine enzymes (SSR1-3, SMO1-3, CPI-5, CYP51G, SMO2-2, C14-R-2, 8,7SI-4, C5-SD1, and 7-DR1-1) from the medicinal plant Paris polyphylla and established detailed biosynthetic routes from cycloartenol to cholesterol. Specfically, we optimized HMGR, a key gene of the mevalonate pathway, and co-expressed it with the PpOSC1 gene to achieve a high level of cycloartenol (28.79 mg/g dry weight, which is a sufficient amount of precursor for cholesterol biosynthesis) synthesis in the leaves of N. benthamiana. Subsequently, using a one-by-one elimination method we found that six of these enzymes (SSR1-3, SMO1-3, CPI-5, CYP51G, SMO2-2, and C5-SD1) were crucial for cholesterol production in N. benthamiana, and we establihed a high-efficiency cholesterol synthesis system with a yield of 5.63 mg/g dry weight. Using this strategy, we also discovered the biosynthetic metabolic network responsible for the synthesis of a common aglycon of steroidal saponin, diosgenin, using cholesterol as a substrate, obtaining a yield of 2.12 mg/g dry weight in N. benthamiana. Our study provides an effective strategy to characterize the metabolic pathways of medicinal plants that lack a system for in vivo functional verification, and also lays a foundation for the synthesis of active steroid saponins in plant chassis.

Recent Advances in Yeast Recombinant Biosynthesis of the Triterpenoid Protopanaxadiol and Glycosylated Derivatives Thereof

Plant natural products are a seemingly endless resource for novel chemical structures. However, their extraction often results in high prices, fluctuation in both quantity and quality, and negative environmental impact. The latter might result from the extraction procedure but more often from the high amount of plant biomass required. With the advent of synthetic biology, producing natural plant products in large quantities using yeasts as hosts has become possible. Here, we focus on the recent advances in metabolic engineering of the yeasts species Saccharomyces cerevisiae and Yarrowia lipolytica for the synthesis of ginsenoside triterpenoids, namely, dammarenediol-II, protopanaxadiol, protopanaxatriol, compound K, ginsenoside Rh1, ginsenoside Rh2, ginsenoside Rg3, and ginsenoside F1. A discussion is provided on advanced synthetic biology, bioprocess strategies, and current challenges for the biosynthesis of ginsenoside triterpenoids. Finally, future directions in metabolic and process engineering are summarized and may help reify sustainable ginsenoside production.

Deletion and tandem duplications of biosynthetic genes drive the diversity of triterpenoids in Aralia elata

Araliaceae species produce various classes of triterpene and triterpenoid saponins, such as the oleanane-type triterpenoids in Aralia species and dammarane-type saponins in Panax, valued for their medicinal properties. The lack of genome sequences of Panax relatives has hindered mechanistic insight into the divergence of triterpene saponins in Araliaceae. Here, we report a chromosome-level genome of Aralia elata with a total length of 1.05 Gb. The loss of 12 exons in the dammarenediol synthase (DDS)-encoding gene in A. elata after divergence from Panax might have caused the lack of dammarane-type saponin production, and a complementation assay shows that overexpression of the PgDDS gene from Panax ginseng in callus of A. elata recovers the accumulation of dammarane-type saponins. Tandem duplication events of triterpene biosynthetic genes are common in the A. elata genome, especially for AeCYP72As, AeCSLMs, and AeUGT73s, which function as tailoring enzymes of oleanane-type saponins and aralosides. More than 13 aralosides are de novo synthesized in Saccharomyces cerevisiae by overexpression of these genes in combination. This study sheds light on the diversity of saponins biosynthetic pathway in Araliaceae and will facilitate heterologous bioproduction of aralosides.