Efficient production of vindoline from tabersonine by metabolically engineered Saccharomyces cerevisiae

Multiplexed engineering of cytochrome P450 enzymes for promoting terpenoid synthesis in Saccharomyces cerevisiae cell factories: A review

Terpenoids, also known as isoprenoids, represent the largest and most structurally diverse family of natural products, and their biosynthesis is closely related to cytochrome P450 enzymes (P450s). Given the limitations of direct extraction from natural resources, such as low productivity and environmental concerns, heterologous expression of P450s in microbial cell factories has emerged as a promising, efficient, and sustainable strategy for terpenoid production. The yeast expression system is a preferred selection for terpenoid synthesis because of its inner membrane system, which is required for eukaryotic P450 expression, and the inherent mevalonate pathway providing precursors for terpenoid synthesis. In this review, we discuss the advanced strategies used to enhance the local enzyme concentration and catalytic properties of P450s in Saccharomyces cerevisiae, with a focus on recent developments in metabolic and protein engineering. Expression enhancement and subcellular compartmentalization are specifically employed to increase the local enzyme concentration, whereas cofactor, redox partner, and enzyme engineering are utilized to improve the catalytic efficiency and substrate specificity of P450s. Subsequently, we discuss the application of P450s for the pathway engineering of terpenoid synthesis and whole-cell biotransformation, which are profitable for the industrial application of P450s in S. cerevisiae chassis. Finally, we explore the potential of using computational and artificial intelligence technologies to rationally design and construct high-performance cell factories, which offer promising pathways for future terpenoid biosynthesis.

Elucidation and de novo reconstitution of glyceollin biosynthesis

Glyceollins are phytoalexins, soybean-produced compounds that respond to pathogen invasion, injury, and environmental challenges. While these compounds have diverse bioactivities, their limited accessibility hinders further physiological and biochemical studies. Additionally, the incomplete understanding of glyceollin biosynthesis, particularly cyclization steps, remains a major barrier to sustainable production through synthetic biology. In this study, we uncover the complete biosynthetic pathway of glyceollins through a combinatorial approach involving transient expression in Nicotiana benthamiana, in vitro enzyme characterization, and yeast feeding studies. We identified previously uncharacterized genes encoding reductases for 7,2',4'-trihydroxyisoflavanol biosynthesis and five P450 enzymes that mediate the final oxidative cyclization to produce glyceollins I, II, and III. By de novo reconstruction of the pathway through synthetic biology and metabolic engineering, we successfully produced glyceollins from simple carbon sources in baker's yeast. This work advances the understanding of glyceollin biosynthesis in soybeans, enables sustainable production in microbial hosts, and offers new opportunities for their application in agriculture and biology.

Synthetic Biology in Natural Product Biosynthesis

Synthetic biology has played an important role in the renaissance of natural products research during the post-genomics era. The development and integration of new tools have transformed the workflow of natural product discovery and engineering, generating multidisciplinary interest in the field. In this review, we summarize recent developments in natural product biosynthesis from three different aspects. First, advances in bioinformatics, experimental, and analytical tools to identify natural products associated with predicted biosynthetic gene clusters (BGCs) will be covered. This will be followed by an extensive review on the heterologous expression of natural products in bacterial, fungal and plant organisms. The native host-independent paradigm to natural product identification, pathway characterization, and enzyme discovery is where synthetic biology has played the most prominent role. Lastly, strategies to engineer biosynthetic pathways for structural diversification and complexity generation will be discussed, including recent advances in assembly-line megasynthase engineering, precursor-directed structural modification, and combinatorial biosynthesis.

Engineering Saccharomyces cerevisiae for De Novo Biosynthesis of 3'-Hydroxygenistein

The polyhydroxy isoflavone 3'-hydroxygenistein (3'-OHG) has a wide range of pharmaceutical and nutraceutical benefits. Therefore, it is important to develop an efficient and sustainable method for 3'-OHG production. Here, we engineered the metabolic pathways of Saccharomyces cerevisiae to achieve de novo biosynthesis of 3'-OHG. First, we screened 2-hydroxyisoflavanone synthase (IFS), cytochrome P450 reductase, and 2-hydroxyisoflavanone dehydratase from different sources and optimized the best combination via promoter engineering. Next, we demonstrated that amplification of the rate-limiting enzyme PlIFS from Pueraria lobata improved genistein production. Increasing the availability of the cofactor heme further increased genistein titer to 44.55 ± 1.82 mg/L. Subsequently, screening and multicopy integration of isoflavone-3'-hydroxylase achieved 13.23 ± 0.27 mg/L 3'-OHG from 100 mg/L naringenin. Finally, 1.40 ± 0.02 mg/L 3'-OHG could be achieved via the de novo biosynthesis pathway. The final strain generated in this study will facilitate the production of polyhydroxy isoflavones via the 3'-OHG biosynthetic pathway.

Evolution of interorganismal strigolactone biosynthesis in seed plants

Strigolactones (SLs) are methylbutenolide molecules derived from β-carotene through an intermediate carlactonoic acid (CLA). Canonical SLs act as signals to microbes and plants, whereas noncanonical SLs are primarily plant hormones. The cytochrome P450 CYP722C catalyzes a critical step, converting CLA to canonical SLs in most angiosperms. Using synthetic biology, we investigated the function of CYP722A, an evolutionary predecessor of CYP722C. CYP722A converts CLA into 16-hydroxy-CLA (16-OH-CLA), a noncanonical SL detected exclusively in the shoots of various flowering plants. 16-OH-CLA application restores control of shoot branching to SL-deficient mutants in Arabidopsis thaliana and is perceived by the SL signaling pathway. We hypothesize that biosynthesis of 16-OH-CLA by CYP722A was a metabolic stepping stone in the evolution of canonical SLs that mediate rhizospheric signaling in many flowering plants.

Tabersonine enhances cisplatin sensitivity by modulating Aurora kinase A and suppressing epithelial-mesenchymal transition in triple-negative breast cancer

CONTEXT

Tabersonine has been investigated for its role in modulating inflammation-associated pathways in various diseases. However, its regulatory effects on triple-negative breast cancer (TNBC) have not yet been fully elucidated.

OBJECTIVE

This study uncovers the anticancer properties of tabersonine in TNBC cells, elucidating its role in enhancing chemosensitivity to cisplatin (CDDP).

MATERIALS AND METHODS

After tabersonine (10 μM) and/or CDDP (10 μM) treatment for 48 h in BT549 and MDA-MB-231 cells, cell proliferation was evaluated using the cell counting kit-8 and colony formation assays. Quantitative proteomics, online prediction tools and molecular docking analyses were used to identify potential downstream targets of tabersonine. Transwell and wound-healing assays and Western blot analysis were used to assess epithelial-mesenchymal transition (EMT) phenotypes.

RESULTS

Tabersonine demonstrated inhibitory effects on TNBC cells, with IC50 values at 48 h being 18.1 μM for BT549 and 27.0 μM for MDA-MB-231. The combined treatment of CDDP and tabersonine synergistically suppressed cell proliferation in BT549 and MDA-MB-231 cells. Enrichment analysis revealed that the proteins differentially regulated by tabersonine were involved in EMT-related signalling pathways. This combination treatment also effectively restricted EMT-related phenotypes. Through the integration of online target prediction and proteomic analysis, Aurora kinase A (AURKA) was identified as a potential downstream target of tabersonine. AURKA expression was reduced in TNBC cells post-treatment with tabersonine.

DISCUSSION AND CONCLUSIONS

Tabersonine significantly enhances the chemosensitivity of CDDP in TNBC cells, underscoring its potential as a promising therapeutic agent for TNBC treatment.

Heterologous production of corosolic acid, a phyto-insulin, in agroinfiltrated Nicotiana benthamiana leaves

Triterpenoids, a group of specialized plant metabolites with substantial structural diversity, are promising for healthcare applications. Ursolic acid, a pentacyclic triterpenoid with therapeutic potential, is also important as a precursor of corosolic acid, which is known as a "phyto-insulin" for its insulin-like properties. Ursolic acid is synthesized from a linear 30-carbon precursor 2,3-oxidosqualene via cyclization to produce triterpene scaffold α-amyrin, followed by a series of oxidation steps at the C-28 position mediated by cytochrome P450 monooxygenases (CYPs) in the CYP716A subfamily. The Tsukuba system was developed for the high-level transient expression of foreign proteins in plant cells based on the use of a binary vector equipped with geminiviral replication system and a double terminator. In this study, we used the Tsukuba system to produce ursolic acid in Nicotiana benthamiana leaves via transient pathway reconstruction. We used an oxidosqualene cyclase identified from the medicinal legume Bauhinia forficata, exhibiting a preponderant α-amyrin-producing activity. Wild-type Medicago truncatula CYP716A12 and its mutants were assessed in terms of ursolic acid production. We improved the performance of MtCYP716A12 by co-expressing it with the appropriate cytochrome P450 reductase (CPR) isozyme as an electron-transfer partner and tested different Agrobacterium infiltration ratios to optimize the CPR : CYP ratio to maximize ursolic acid production. We also achieved high yield of corosolic acid by co-expressing Avicennia marina CYP716C53 with ursolic acid biosynthetic enzymes. Moreover, engineering of AmCYP716C53 significantly improved corosolic acid yield, resulting in a yield exceeding the content found in banaba leaves, a well-known rich source of corosolic acid.

Visible-Light-Induced Dearomative Annulation of Indoles toward Stereoselective Formation of Fused- and Spiro Indolines

Dearomatization approaches are attractive for their abilities to transform simple, planar arenes into complex, three-dimensional architectures. In particular, visible-light driven dearomatization strategies are significant because of their mild, green, and sustainable nature, enabling the fabrication of new chemical bonds via an electron transfer or energy transfer process. Indole compounds, being potentially bioactive and readily accessible, can be employed efficiently as building blocks for constructing diverse annulated frameworks under photocatalysis. Highly stereoselective radical cascade reactions of appropriate indole systems can provide complex cyclic scaffolds bearing multiple stereocenters. In fact, the past few years have witnessed the renaissance of dearomative cycloadditions of indoles via visible-light-induced photocatalysis. The present review highlights recent advances (2019-mid 2024) in visible-light-driven dearomative annulation of indoles leading to formation of polycyclic indolines, including angularly fused and spiro indolines. Most of the reactions described in this review are simple, providing quick access to the desired products. Additionally, characteristic reaction mechanisms are offered to provide an understand of how indole scaffolds show distinctive reactivity under photocatalytic conditions.

Research progress on the pharmacological activity, biosynthetic pathways, and biosynthesis of crocins

Crocins are water-soluble apocarotenoids isolated from the flowers of crocus and gardenia. They exhibit various pharmacological effects, including neuroprotection, anti-inflammatory properties, hepatorenal protection, and anticancer activity. They are often used as coloring and seasoning agents. Due to the limited content of crocins in plants and the high cost of chemical synthesis, the supply of crocins is insufficient to meet current demand. The biosynthetic pathways for crocins have been elucidated to date, which allows the heterologous production of these valuable compounds in microorganisms by fermentation. This review article provides a comprehensive overview of the chemistry, pharmacological activity, biosynthetic pathways, and heterologous production of crocins, aiming to lay the foundation for the large-scale production of these valuable natural products by using engineered microbial cell factories.

Progress in Gene Editing and Metabolic Regulation of Saccharomyces cerevisiae with CRISPR/Cas9 Tools

The CRISPR/Cas9 systems have been developed as tools for genetic engineering and metabolic engineering in various organisms. In this review, various aspects of CRISPR/Cas9 in Saccharomyces cerevisiae, from basic principles to practical applications, have been summarized. First, a comprehensive review has been conducted on the history of CRISPR/Cas9, successful cases of gene disruptions, and efficiencies of multiple DNA fragment insertions. Such advanced systems have accelerated the development of microbial engineering by reducing time and labor, and have enhanced the understanding of molecular genetics. Furthermore, the research progress of the CRISPR/Cas9-based systems in the production of high-value-added chemicals and the improvement of stress tolerance in S. cerevisiae have been summarized, which should have an important reference value for genetic and synthetic biology studies based on S. cerevisiae.

Regulation of T16H subcellular localization for promoting its catalytic efficiency in yeast cells

To investigate the effect of subcellular localization on the transformation efficiency of heterologous expressed functional P450s in yeast. Microbial biotransformation offers a promising substitute for the direct extraction of natural products, but its viability in industrial applications depends on achieving high transformation efficiencies. To investigate the influence of subcellular microenvironments on the activity of heterologously expressed P450s, Catharanthus roseus tabersonine 16-hydroxylase (T16H) was chosen, and its subcellular localization was regulated by fusing organelle-localization signals. Interestingly, this manipulation had no effect on the gene expression levels of T16H, but resulted in varying conversion rates from tabersonine to 16-hydroxy tabersonine. Notably, the highest transformation efficiency was observed in yeast cells expressing peroxisome-localized T16H. Given the alkaline pH optimum for P450s, the alkaline peroxisomal lumen could be a suitable compartment for P450s reactions to achieve high transformation efficiency using yeast cells. Different organelle-localization of T16H in yeast cells resulted in varying conversion rates, suggesting that compartmentalizing the expression of target enzymes could be a viable approach to increase transformation efficiency in yeast.

Early-stage economic and environmental impact assessment for optimized bioprocess development: Monoterpenoid indole alkaloids

Microbial refactoring offers sustainable production of plant-sourced pharmaceuticals associated with high production costs, ecological harms, and supply chain dependencies. Here, microbial tabersonine production in Saccharomyces cerevisiae is modeled during early-stage development (TRL: 3-5), guiding decisions for process-scale economic and environmental optimization. The base-case 0.7 mg/L titer indicated a minimum selling price (MSP) of $3,910,000/kg and global warming potential (GWP) of 2,540 kgCO2eq/g. The industrial process at 1 g/L resulted in an MSP of 4,262 $/kg and a GWP of 6.36 kgCO2eq/g. Location analysis indicated a sustainability trade-off between France, USA, Poland, and China, with the written order of declining MSP and increasing GWP. Continuous processing promised reducing the MSP by 18-27 %, and the GWP by 17-31 %. In-situ product extraction during fermentation was estimated to lower the MSP by 41-61 %, and the GWP by 30-75 %. In addition to showcasing a combined TEA-LCA on biopharmaceuticals, the early-stage assessment approach guides bioprocess optimization.

Strategies on biosynthesis and production of bioactive compounds in medicinal plants

Medicinal plants are a valuable source of essential medicines and herbal products for healthcare and disease therapy. Compared with chemical synthesis and extraction, the biosynthesis of natural products is a very promising alternative for the successful conservation of medicinal plants, and its rapid development will greatly facilitate the conservation and sustainable utilization of medicinal plants. Here, we summarize the advances in strategies and methods concerning the biosynthesis and production of natural products of medicinal plants. The strategies and methods mainly include genetic engineering, plant cell culture engineering, metabolic engineering, and synthetic biology based on multiple "OMICS" technologies, with paradigms for the biosynthesis of terpenoids and alkaloids. We also highlight the biosynthetic approaches and discuss progress in the production of some valuable natural products, exemplifying compounds such as vindoline (alkaloid), artemisinin and paclitaxel (terpenoids), to illustrate the power of biotechnology in medicinal plants.

Anthriscus sylvestris Deoxypodophyllotoxin Synthase Involved in the Podophyllotoxin Biosynthesis

Tetrahydrofuran ring formation from dibenzylbutyrolactone lignans is a key step in the biosynthesis of aryltetralin lignans including deoxypodophyllotoxin and podophyllotoxin. Previously, Fe(II)- and 2-oxoglutarate-dependent dioxygenase (2-ODD) from Podophyllum hexandrum (Himalayan mayapple, Berberidaceae) was found to catalyze the cyclization of a dibenzylbutyrolactone lignan, yatein, to give deoxypodophyllotoxin and designated as deoxypodophyllotoxin synthase (DPS). Recently, we reported that the biosynthesis of deoxypodophyllotoxin and podophyllotoxin evolved in a lineage-specific manner in phylogenetically unrelated plant species such as P. hexandrum and Anthriscus sylvestris (cow parsley, Apiaceae). Therefore, a comprehensive understanding of the characteristics of DPSs that catalyze the cyclization of yatein to deoxypodophyllotoxin in various plant species is important. However, for plant species other than P. hexandrum, the isolation of the DPS enzyme gene and the type of the enzyme, e.g. whether it is 2-ODD or another type of enzyme such as cytochrome P-450, have not been reported. In this study, we report the identification and characterization of A. sylvestris DPS (AsDPS). Phylogenetic analysis showed that AsDPS belonged to the 2-ODD superfamily and shared moderate amino acid sequence identity (40.8%) with P. hexandrum deoxypodophyllotoxin synthase (PhDPS). Recombinant protein assay indicated that AsDPS and PhDPS differ in terms of the selectivity of substrate enantiomers. Protein modeling using AlphaFold2 and site-directed mutagenesis indicated that the Tyr305 residue of AsDPS probably contributes to substrate recognition. This study advances our understanding of the podophyllotoxin biosynthetic pathway in A. sylvestris and provides new insight into 2-ODD involved in plant secondary (specialized) metabolism.

Advances in Metabolic Engineering of Plant Monoterpene Indole Alkaloids

Monoterpene indole alkaloids (MIAs) encompass a diverse family of over 3000 plant natural products with a wide range of medical applications. Further utilizations of these compounds, however, are hampered due to low levels of abundance in their natural sources, causing difficult isolation and complex multi-steps in uneconomical chemical syntheses. Metabolic engineering of MIA biosynthesis in heterologous hosts is attractive, particularly for increasing the yield of natural products of interest and expanding their chemical diversity. Here, we review recent advances and strategies which have been adopted to engineer microbial and plant systems for the purpose of generating MIAs and discuss the current issues and future developments of manufacturing MIAs by synthetic biology approaches.

Improved protein glycosylation enabled heterologous biosynthesis of monoterpenoid indole alkaloids and their unnatural derivatives in yeast

With over 3000 reported structures, monoterpenoid indole alkaloids (MIAs) constitute one of the largest alkaloid groups in nature, including the clinically important anticancer drug vinblastine and its semi-synthetic derivatives from Catharanthus roseus (Madagascar's periwinkle). With the elucidation of the complete 28-step biosynthesis for anhydrovinblastine, it is possible to investigate the heterologous production of vinblastine and other medicinal MIAs. In this study, we successfully expressed the flavoenzyme O-acetylstemmadenine oxidase in Saccharomyces cerevisiae (baker's yeast) by signal peptide modification, which is a vinblastine biosynthetic gene that has not been functionally expressed in this system. We also reported the simultaneous integration of ∼18 kb MIA biosynthetic gene cassettes as single copies into four genomic loci of baker's yeast by CRISPR-Cas9, which enabled the biosynthesis of vinblastine precursors catharanthine and tabersonine from the feedstocks secologanin and tryptamine. We further demonstrated the biosynthesis of fluorinated and hydroxylated catharanthine and tabersonine derivatives using our yeasts, which showed that the MIA biosynthesis accommodates unnatural substrates, and the system can be further explored to produce other complex MIAs.

In Silico Prediction and Mining of Exporters for Secretory Bioproduction of Terpenoids in Saccharomyces cerevisiae

Terpenoids are the largest class of natural products, and their bioproduction by engineered cell factories receives high attention. However, excessive intracellular accumulation is one of the bottlenecks that limit the further improvement of the yield of terpenoid products. Therefore, it is important to mine exporters to achieve the secretory production of terpenoids. This study proposed a framework for the in silico prediction and mining of terpenoid exporters in Saccharomyces cerevisiae. Through the process of "mining-docking-construction-validation", we found that Pdr5 of ATP-binding cassette (ABC) transporters and Osh3 of oxysterol-binding homology (Osh) proteins can promote squalene efflux. Squalene secretion of the strain overexpressing Pdr5 and Osh3 increased to 141.1 times that of the control strain. Besides squalene, ABC exporters also can promote the secretion of β-carotene and retinal. Molecular dynamics simulation results revealed that before exporter conformations transitioned to the "outward-open" states, the substrates might have bound to the tunnels and prepared for rapid efflux. Overall, this study provides a terpenoid exporter prediction and mining framework that may be generally used to identify exporters of other terpenoids.

Cell type matters: competence for alkaloid metabolism differs in two seed-derived cell strains of Catharanthus roseus

Since the discovery of the anticancer drugs vinblastine and vincristine, Catharanthus roseus has been intensively studied for biosynthesis of several terpene indole alkaloids (TIAs). Due to their low abundance in plant tissues at a simultaneously high demand, modes of production alternative to conventional extraction are mandatory. Plant cell fermentation might become one of these alternatives, yet decades of research have shown limited success to certain product classes, leading to the question: how to preserve the intrinsic ability to produce TIAs (metabolic competence) in cell culture? We used the strategy to use the developmental potency of mature embryos to generate such strains. Two cell strains (C1and C4) from seed embryos of Catharanthus roseus were found to differ not only morphologically, but also in their metabolic competence. This differential competence became manifest not only under phytohormone elicitation, but also upon feeding with alkaloid pathway precursors. The more active strain C4 formed larger cell aggregates and was endowed with longer mitochondria. These cellular features were accompanied by higher alkaloid accumulation in response to methyl jasmonate (MeJA) elicitation. The levels of catharanthine could be increased significantly, while the concurrent vindoline branch of the pathway was blocked, such that no bisindole alkaloids were detectable. By feeding vindoline to MeJA-elicited C4 cells, vincristine became detectable; however, only to marginal amounts. In conclusion, these results show that cultured cells are not "de-differentiated", but can differ in metabolic competence. In addition to elicitation and precursor feeding, the cellular properties of the "biomatter" are highly relevant for the success of plant cell fermentation.

Engineering the Biosynthesis of Late-Stage Vinblastine Precursors Precondylocarpine Acetate, Catharanthine, Tabersonine in Nicotiana benthamiana

Vinblastine is a chemotherapy agent produced by the plant Catharanthus roseus in small quantities. Currently, vinblastine is sourced by isolation or semisynthesis. Nicotiana benthamiana is a plant heterologous host that can be used for reconstitution of biosynthetic pathways as an alternative natural product sourcing strategy. Recently, the biosynthesis of the late-stage vinblastine precursors precondylocarpine acetate, catharanthine, and tabersonine have been fully elucidated. However, the large number of enzymes involved in the pathway and the unstable nature of intermediates make the reconstitution of late-stage vinblastine precursor biosynthesis challenging. We used the N. benthamiana chassis and a state-of-art modular vector assembly to optimize the six biosynthetic steps leading to production of precondylocarpine acetate from the central intermediate strictosidine (∼2.7 mg per 1 g frozen tissue). After selecting the optimal regulatory element combination, we constructed four transcriptional unit assemblies and tested their efficiency. Finally, we successfully reconstituted the biosynthetic steps leading to production of catharanthine and tabersonine.

De Novo Biosynthesis of Vindoline and Catharanthine in Saccharomyces cerevisiae

Vinblastine has been used clinically as one of the most potent therapeutics for the treatment of several types of cancer. However, the traditional plant extraction method suffers from unreliable supply, low abundance, and extremely high cost. Here, we use synthetic biology approach to engineer Saccharomyces cerevisiae for de novo biosynthesis of vindoline and catharanthine, which can be coupled chemically or biologically to vinblastine. On the basis of a platform strain with sufficient supply of precursors and cofactors for biosynthesis, we reconstituted, debottlenecked, and optimized the biosynthetic pathways for the production of vindoline and catharanthine. The vindoline biosynthetic pathway represents one of the most complicated pathways ever reconstituted in microbial cell factories. Using shake flask fermentation, our engineered yeast strains were able to produce catharanthine and vindoline at a titer of 527.1 and 305.1 μg·liter-1, respectively, without accumulating detectable amount of pathway intermediates. This study establishes a representative example for the production of valuable plant natural products in yeast.

The Vinca minor genome highlights conserved evolutionary traits in monoterpene indole alkaloid synthesis

Vinca minor, also known as the lesser periwinkle, is a well-known species from the Apocynaceae, native to central and southern Europe. This plant synthesizes monoterpene indole alkaloids, which are a class of specialized metabolites displaying a wide range of bioactive- and pharmacologically important properties. Within the almost 50 monoterpene indole alkaloids it produces, V. minor mainly accumulates vincamine, which is commercially used as a nootropic. Using a combination of Oxford Nanopore Technologies long read- and Illumina short-read sequencing, a 679,098 Mb V. minor genome was assembled into 296 scaffolds with an N50 scaffold length of 6 Mb, and encoding 29,624 genes. These genes were functionally annotated and used in a comparative genomic analysis to establish gene families and to investigate gene family expansion and contraction across the phylogenetic tree. Furthermore, homology-based monoterpene indole alkaloid gene predictions together with a metabolic analysis across 4 different V. minor tissue types guided the identification of candidate monoterpene indole alkaloid genes. These candidates were finally used to identify monoterpene indole alkaloid gene clusters, which combined with synteny analysis allowed for the discovery of a functionally validated vincadifformine-16-hydroxylase, reinforcing the potential of this dataset for monoterpene indole alkaloids gene discovery. It is expected that access to these resources will facilitate the elucidation of unknown monoterpene indole alkaloid biosynthetic routes with the potential of transferring these pathways to heterologous expression systems for large-scale monoterpene indole alkaloid production.

More than a Catharanthus plant: A multicellular and pluri-organelle alkaloid-producing factory

Plants represent a huge reservoir of natural products. A broad series of these compounds now find application for human health. In this respect, the monoterpene indole alkaloids (MIAs), particularly from Madagascar periwinkle, are a prominent example of plant specialized metabolites with an important therapeutic potential. However, the supply of MIA drugs has always been a challenge since the low-yield accumulation in planta. This mainly results from the complex architecture of the MIA biosynthetic pathway that involves several organs, tissue types and subcellular organelles. Here, we describe the most recent advances towards the elucidation of this pathway route as well as its spatial organization in planta. Besides allowing a better understanding of the MIA biosynthetic flux in the whole plant, such knowledge will also probably pave the way for the development of metabolic engineering strategies to sustain the MIA supply.

Engineering Catharanthus roseus monoterpenoid indole alkaloid pathway in yeast

Catharanthus roseus (Madagascar periwinkle), a medicinal plant possessing high pharmacological attributes, is widely recognized for the biosynthesis of anticancer monoterpenoid indole alkaloids (MIAs) - vinblastine and vincristine. The plant is known to biosynthesize more than 130 different bioactive MIAs, highly acclaimed in traditional and modern medicinal therapies. The MIA biosynthesis is strictly regulated at developmental and spatial-temporal stages and requires a well-defined cellular and sub-cellular compartmentation for completion of the entire MIAs biosynthesis. However, due to their cytotoxic nature, the production of vinblastine and vincristine occurs in low concentrations in planta and the absence of chemical synthesis alternatives projects a huge gap in demand and supply, leading to high market price. With research investigations spanning more than four decades, plant tissue culture and metabolic engineering (ME)-based studies were attempted to explore, understand, explain, improve and enhance the MIA biosynthesis using homologous and heterologous systems. Presently, metabolic engineering and synthetic biology are the two powerful tools that are contributing majorly in elucidating MIA biosynthesis. This review concentrates mainly on the efforts made through metabolic engineering of MIAs in heterologous microbial factories. KEY POINTS: • Yeast engineering provides alternative production source of phytomolecules • Yeast engineering also helps to discover missing plant pathway enzymes and genes.

Metabolic Engineering of Saccharomyces cerevisiae for High-Level Production of Chlorogenic Acid from Glucose

Chlorogenic acid (CGA), a major dietary phenolic compound, has been increasingly used in the food and pharmaceutical industries because of its ready availability and extensive biological and pharmacological activities. Traditionally, extraction from plants has been the main approach for the commercial production of CGA. This study reports the first efficient microbial production of CGA by engineering the yeast, Saccharomyces cerevisiae, on a simple mineral medium. First, an optimized de novo biosynthetic pathway for CGA was reconstructed in S. cerevisiae from glucose with a CGA titer of 36.6 ± 2.4 mg/L. Then, a multimodule engineering strategy was employed to improve CGA production: (1) unlocking the shikimate pathway and optimizing carbon distribution; (2) optimizing the l-Phe branch and pathway balancing; and (3) increasing the copy number of CGA pathway genes. The combination of these interventions resulted in an about 6.4-fold improvement of CGA titer up to 234.8 ± 11.1 mg/L in shake flask cultures. CGA titers of 806.8 ± 1.7 mg/L were achieved in a 1 L fed-batch fermenter. This study opens a route to effectively produce CGA from glucose in S. cerevisiae and establishes a platform for the biosynthesis of CGA-derived value-added metabolites.

High-yield bioactive triterpenoid production by heterologous expression in Nicotiana benthamiana using the Tsukuba system

Oleanolic acid is a pentacyclic triterpenoid found in numerous plant species and is a precursor to several bioactive triterpenoids with commercial potential. However, oleanolic acid accumulates at low levels in plants, and its chemical synthesis is challenging. Here, we established a method for producing oleanolic acid in substantial quantities via heterologous expression of pathway enzymes in Nicotiana benthamiana. The "Tsukuba system" is one of the most efficient agroinfiltration-based transient protein expression systems using the vector pBYR2HS, which contains geminiviral replication machinery and a double terminator for boosting expression. Additionally, the pBYR2HS vector contains an expression cassette for the gene-silencing suppressor p19 protein from tomato bushy stunt virus, which can also contribute to enhancing the expression of target proteins. In this study, we evaluated the applicability of this system to heterologous triterpenoid production in N. benthamiana. Medicago truncatula cytochrome P450 monooxygenase (CYP) 716A12 is the first enzyme to be functionally characterized as β-amyrin C-28 oxidase producing oleanolic acid. A mutant CYP716A12 (D122Q) with improved catalytic activity engineered in our previous study was co-expressed with other enzymes in N. benthamiana leaves. Using pBYR2HS, oleanolic acid yield was increased 13.1-fold compared with that using the conventional binary vector, indicating the advantage of the Tsukuba system. We also demonstrated the efficacy of co-expressing a mutant Arabidopsis thaliana HMGR1 catalytic domain, additional NADPH-cytochrome P450 reductase (CPR) transferring electrons to heterologous CYPs, and application of ascorbic acid for preventing leaf necrosis after agroinfiltration, to improve product yield. As a result, the product yields of both simple (β-amyrin) and oxidized (oleanolic acid and maslinic acid) triterpenoids were significantly improved compared with the previously reported yield in heterologous triterpenoid production in N. benthamiana leaves.