Biotechnological Production of Flavonoids: An Update on Plant Metabolic Engineering, Microbial Host Selection, and Genetically Encoded Biosensors

State-of-the-art in engineering small molecule biosensors and their applications in metabolic engineering

Genetically encoded biosensors are crucial for enhancing our understanding of how molecules regulate biological systems. Small molecule biosensors, in particular, help us understand the interaction between chemicals and biological processes. They also accelerate metabolic engineering by increasing screening throughput and eliminating the need for sample preparation through traditional chemical analysis. Additionally, they offer significantly higher spatial and temporal resolution in cellular analyte measurements. In this review, we discuss recent progress in in vivo biosensors and control systems-biosensor-based controllers-for metabolic engineering. We also specifically explore protein-based biosensors that utilize less commonly exploited signaling mechanisms, such as protein stability and induced degradation, compared to more prevalent transcription factor and allosteric regulation mechanism. We propose that these lesser-used mechanisms will be significant for engineering eukaryotic systems and slower-growing prokaryotic systems where protein turnover may facilitate more rapid and reliable measurement and regulation of the current cellular state. Lastly, we emphasize the utilization of cutting-edge and state-of-the-art techniques in the development of protein-based biosensors, achieved through rational design, directed evolution, and collaborative approaches.

Engineering a Plant Polyketide Synthase for the Biosynthesis of Methylated Flavonoids

Homoeriodictyol and hesperetin are naturally occurring O-methylated flavonoids with many health-promoting properties. They are produced in plants in low abundance and as complex mixtures of similar compounds that are difficult to separate. Synthetic biology offers the opportunity to produce various flavonoids in a targeted, bottom-up approach in engineered microbes with high product titers. However, the production of O-methylated flavonoids is currently still highly inefficient. In this study, we investigated and engineered a combination of enzymes that had previously been shown to support homoeriodictyol and hesperetin production in Escherichia coli from fed O-methylated hydroxycinnamic acids. We determined the crystal structures of the enzyme catalyzing the first committed step of the pathway, chalcone synthase from Hordeum vulgare, in three ligand-bound states. Based on these structures and a multiple sequence alignment with other chalcone synthases, we constructed mutant variants and assessed their performance in E. coli toward producing methylated flavonoids. With our best mutant variant, HvCHS (Q232P, D234 V), we were able to produce homoeriodictyol and hesperetin at 2 times and 10 times higher titers than reported previously. Our findings will facilitate further engineering of this enzyme toward higher production of methylated flavonoids.

Heterologous Naringenin Production in the Filamentous Fungus Penicillium rubens

Naringenin is a natural product with several reported bioactivities and is the key intermediate for the entire class of plant flavonoids. The translation of flavonoids into modern medicine as pure compounds is often hampered by their low abundance in nature and their difficult chemical synthesis. Here, we investigated the possibility to use the filamentous fungus Penicillium rubens as a host for flavonoid production. P. rubens is a well-characterized, highly engineered, traditional "workhorse" for the production of β-lactam antibiotics. We integrated two plant genes encoding enzymes in the naringenin biosynthesis pathway into the genome of the secondary metabolite-deficient P. rubens 4xKO strain. After optimization of the fermentation conditions, we obtained an excellent molar yield of naringenin from fed p-coumaric acid (88%) with a titer of 0.88 mM. Along with product accumulation over 36 h, however, we also observed rapid degradation of naringenin. Based on high-resolution mass spectrometry analysis, we propose a naringenin degradation pathway in P. rubens 4xKO, which is distinct from other flavonoid-converting pathways reported in fungi. Our work demonstrates that P. rubens is a promising host for recombinant flavonoid production, and it represents an interesting starting point for further investigation into the utilization of plant biomass by filamentous fungi.

Challenges and opportunities for engineered Escherichia coli as a pivotal chassis toward versatile tyrosine-derived chemicals production

Growing concerns over limited fossil resources and associated environmental problems are motivating the development of sustainable processes for the production of high-volume fuels and high-value-added compounds. The shikimate pathway, an imperative pathway in most microorganisms, is branched with tyrosine as the rate-limiting step precursor of valuable aromatic substances. Such occurrence suggests the shikimate pathway as a promising route in developing microbial cell factories with multiple applications in the nutraceutical, pharmaceutical, and chemical industries. Therefore, an increasing number of studies have focused on this pathway to enable the biotechnological manufacture of pivotal and versatile aromatic products. With advances in genome databases and synthetic biology tools, genetically programmed Escherichia coli strains are gaining immense interest in the sustainable synthesis of chemicals. Engineered E. coli is expected to be the next bio-successor of fossil fuels and plants in commercial aromatics synthesis. This review summarizes successful and applicable genetic and metabolic engineering strategies to generate new chassis and engineer the iterative pathway of the tyrosine route in E. coli, thus addressing the opportunities and current challenges toward the realization of sustainable tyrosine-derived aromatics.

Designing plant flavonoids: harnessing transcriptional regulation and enzyme variation to enhance yield and diversity

Plant synthetic biology has emerged as a powerful and promising approach to enhance the production of value-added metabolites in plants. Flavonoids, a class of plant secondary metabolites, offer numerous health benefits and have attracted attention for their potential use in plant-based products. However, achieving high yields of specific flavonoids remains challenging due to the complex and diverse metabolic pathways involved in their biosynthesis. In recent years, synthetic biology approaches leveraging transcription factors and enzyme diversity have demonstrated promise in enhancing flavonoid yields and expanding their production repertoire. This review delves into the latest research progress in flavonoid metabolic engineering, encompassing the identification and manipulation of transcription factors and enzymes involved in flavonoid biosynthesis, as well as the deployment of synthetic biology tools for designing metabolic pathways. This review underscores the importance of employing carefully-selected transcription factors to boost plant flavonoid production and harnessing enzyme promiscuity to broaden flavonoid diversity or streamline the biosynthetic steps required for effective metabolic engineering. By harnessing the power of synthetic biology and a deeper understanding of flavonoid biosynthesis, future researchers can potentially transform the landscape of plant-based product development across the food and beverage, pharmaceutical, and cosmetic industries, ultimately benefiting consumers worldwide.

Biological valorization of lignin to flavonoids

Lignin is the most affluent natural aromatic biopolymer on the earth, which is the promising renewable source for valuable products to promote the sustainability of biorefinery. Flavonoids are a class of plant polyphenolic secondary metabolites containing the benzene ring structure with various biological activities, which are largely applied in health food, pharmaceutical, and medical fields. Due to the aromatic similarity, microbial conversion of lignin derived aromatics to flavonoids could facilitate flavonoid biosynthesis and promote the lignin valorization. This review thereby prospects a novel valorization route of lignin to high-value natural products and demonstrates the potential advantages of microbial bioconversion of lignin to flavonoids. The biodegradation of lignin polymers is summarized to identify aromatic monomers as momentous precursors for flavonoid synthesis. The biosynthesis pathways of flavonoids in both plants and strains are introduced and compared. After that, the key branch points and important intermediates are clearly discussed in the biosynthesis pathways of flavonoids. Moreover, the most significant enzyme reactions including Claisen condensation, cyclization and hydroxylation are demonstrated in the biosynthesis pathways of flavonoids. Finally, current challenges and potential future strategies are also discussed for transforming lignin into various flavonoids. The holistic microbial conversion routes of lignin to flavonoids could make a sustainable production of flavonoids and improve the feasibility of lignin valorization.

Flavonoid Production: Current Trends in Plant Metabolic Engineering and De Novo Microbial Production

Flavonoids are secondary metabolites that represent a heterogeneous family of plant polyphenolic compounds. Recent research has determined that the health benefits of fruits and vegetables, as well as the therapeutic potential of medicinal plants, are based on the presence of various bioactive natural products, including a high proportion of flavonoids. With current trends in plant metabolite research, flavonoids have become the center of attention due to their significant bioactivity associated with anti-cancer, antioxidant, anti-inflammatory, and anti-microbial activities. However, the use of traditional approaches, widely associated with the production of flavonoids, including plant extraction and chemical synthesis, has not been able to establish a scalable route for large-scale production on an industrial level. The renovation of biosynthetic pathways in plants and industrially significant microbes using advanced genetic engineering tools offers substantial promise for the exploration and scalable production of flavonoids. Recently, the co-culture engineering approach has emerged to prevail over the constraints and limitations of the conventional monoculture approach by harnessing the power of two or more strains of engineered microbes to reconstruct the target biosynthetic pathway. In this review, current perspectives on the biosynthesis and metabolic engineering of flavonoids in plants have been summarized. Special emphasis is placed on the most recent developments in the microbial production of major classes of flavonoids. Finally, we describe the recent achievements in genetic engineering for the combinatorial biosynthesis of flavonoids by reconstructing synthesis pathways in microorganisms via a co-culture strategy to obtain high amounts of specific bioactive compounds.

The novel distribution of intracellular and extracellular flavonoids produced by Aspergillus sp. Gbtc 2, an endophytic fungus from Ginkgo biloba root

Here, we reported a Ginkgo endophyte, Aspergillus sp. Gbtc 2, isolated from the root tissue. Its flavonoid biosynthesis pathway was reconstructed, the effect of phenylalanine on the production of flavonoids was explored, and the flavonoid metabolites were identified with the high-resolution Liquid chromatography–mass spectrometry (LC–MS). Some essential genes were annotated to form the upstream of the complete biosynthesis pathway, indicating that Aspergillus sp. Gbtc 2 has the ability to synthesize the C6–C3–C6 flavonoid monomers. HPLC results showed that adding an appropriate amount of phenylalanine could promote the production of flavonoids by Aspergillus Gbtc 2. LC–MS results depicted a significant difference in many flavonoids between intracellularly and extracellularly. Most of the flavonoids gathered in the cell contained glycosylation groups, while almost all components with multiple hydroxyls showed much higher concentrations extracellularly than intracellularly; they likely have different biological functions. A variety of these substances can be mapped back to the pathway pattern of flavonoid biosynthesis and prove the ability of flavonoid production once again. This study expanded the information on flavonoid biosynthesis in Aspergillus and provided a solid theoretical basis for developing the fungi into genetically engineered strains undertaking flavonoid industrialized production.

Enzymatic synthesis of novel unnatural phenoxodiol glycosides with a glycosyl donor flexible glycosyltransferase MeUGT1

Isoflavonoids are of great interest due to their human health-promoting properties, which have resulted in studies on exploiting these phytochemicals as hotspots in diverse bio -industries. Biocatalytic glycosylation of isoflavonoid aglycones to glycosides has attracted marked interests because it enable the biosynthesis of isoflavonoid glycosides with high selectivity under mild conditions, and also provide an environmentally friendly option for the chemical synthesis. Thus, these inspired us to exploit new flexible and effective glycosyltransferases from microbes for making glycosides attractive compounds that are in high demand in several industries. Most recently, we have reported the functional characterization of a bacterial-origin recombinant glycosyltransferase (MeUGT1). Herein, more detailed kinetic characteristics of this biocatalyst, using a number of glycosyl donor substrates, were examined for further investigation of its biocatalytic applicability, enabling it feasible to biosynthesize new glycosides; phenoxodiol-4'-O-α-glucuronide, phenoxodiol-4'-O-α-(2''-N-acetyl)glucosaminide, phenoxodiol-4'-O-α-galactoside, phenoxodiol-4'-O-α-(2''-N-acetyl)galactosaminide and phenoxodiol-4'-O-α-(2''-deoxy)glucoside. The thorough kinetic analyses revealed that while the recombinant enzyme can utilize, albeit with different substrate preference and catalytic efficiency, a total five different nucleotide sugars as glycosyl donors, exhibiting its promiscuity towards glycosyl donors. This is the first report that a recombinant glycosyltransferase MeUGT1 that can regio-specifically glycosylate C4'-hydroxyl function of semi-synthetic phenoxodiol isoflavene to biosynthesize a series of unnatural phenoxodiol-4'-O-α-glycosides.

Flavonoids a Bioactive Compound from Medicinal Plants and Its Therapeutic Applications

Plants generally secrete secondary metabolites in response to stress. These secondary metabolites are very useful for humankind as they possess a wide range of therapeutic activities. Secondary metabolites produced by plants include alkaloids, flavonoids, terpenoids, and steroids. Flavonoids are one of the classes of secondary metabolites of plants found mainly in edible plant parts such as fruits, vegetables, stems, grains, and bark. They are synthesized by the phenylpropanoid pathway. Flavonoids possess antibacterial, antiviral, antioxidant, anti-inflammatory, antimutagenic, and anticarcinogenic properties. Due to their various therapeutic applications, various pharmaceutical companies have exploited different plants for the production of flavonoids. To overcome this situation, various biotechnological strategies have been incorporated to improve the production of different types of flavonoids. In this review, we have highlighted the various types of flavonoids, their biosynthesis, properties, and different strategies to enhance the production of flavonoids.

Biosynthesis of eriodictyol from tyrosine by Corynebacterium glutamicum

Background

Eriodictyol is a bioactive flavonoid compound that shows potential applications in medicine development and food processing. Microbial synthesis of eriodictyol has been attracting increasing attention due to several benefits. In this study, we employed a GRAS strain Corynebacterium glutamicum as the host to produce eriodictyol directly from tyrosine.

Results

We firstly optimized the biosynthetic module of naringenin, the upstream intermediate for eriodictyol production, through screening of different gene orthologues. Next, to improve the level of the precursor malonyl-CoA necessary for naringenin production, we introduced matB and matC from Rhizobium trifolii into C. glutamicum to convert extracellular malonate to intracellular malonyl-CoA. This combinatorial engineering resulted in around 35-fold increase in naringenin production from tyrosine compared to the initial recombinant C. glutamicum. Subsequently, the hpaBC genes from E. coli encoding 4-hydroxyphenylacetate 3-hydroxylase were expressed in C. glutamicum to synthesize eriodictyol from naringenin. Further optimization of the biotransformation process parameters led to the production of 14.10 mg/L eriodictyol.

Conclusions

The biosynthesis of the ortho-hydroxylated flavonoid eriodictyol in C. glutamicum was achieved for the first time via functional expression of E. coli hpaBC, providing a baseline strain for biosynthesis of other complex flavonoids. Our study demonstrates the potential application of C. glutamicum as a host microbe for the biosynthesis of value-added natural compounds from tyrosine.

Strategy for anthocyanins production: From efficient green extraction to novel microbial biosynthesis

Anthocyanins are widely distributed in nature and exhibit brilliant colors and multiple health-promoting effects; therefore, they are extensively incorporated into foods, pharmaceuticals, and cosmetic industries. Anthocyanins have been traditionally produced by plant extraction, which is characterized by high expenditure, low production rates, and rather complex processes, and hence cannot meet the increasing market demand. In addition, the emerging environmental issues resulting from traditional solvent extraction technologies necessitate a more efficient and eco-friendly alternative strategy for producing anthocyanins. This review summarizes the efficient approach for green extraction and introduces a novel strategy for microbial biosynthesis of anthocyanins, emphasizing the technological changes in production.

Chemical Structure, Sources and Role of Bioactive Flavonoids in Cancer Prevention: A Review

There has been a major shift in the collective mindset around the world in recent decades, both in terms of food and in terms of the treatment of chronic diseases. Increasing numbers of people are choosing to prevent rather than treat, which is why many consumers are choosing plant-based diets, mainly due to their bioactive compounds. A significant case of bioactive compound is flavonoids-a wide subclass of an even wider class of phytochemicals: polyphenols. Flavonoids are a broad topic of study for researchers due to their potential in the prevention and treatment of a broad range of cancers. The aim of this review is to inform/update the reader on the diversity, accessibility and importance of flavonoids as biomolecules that are essential for optimal health, focusing on the potential of these compounds in the prevention of various types of cancer. Along with conventional sources, this review presents some of the possible methods for obtaining significant amounts of flavonoids based on a slightly different approach, genetic manipulation.

Rational engineering in Escherichia coli for high-titer production of baicalein based on genome-scale target identification

Baicalein is a bioactive flavonoid isolated from the traditional Chinese medicinal plant, Scutellaria baicalensis Georgi. Microbial synthesis of flavonoids has been intensively developed owing to the eco-friendly nature of the process. However, the titer of the flavonoids obtained is still at a low level, and effective methods to enhance these titers are lacking. In this study, the synthetic performance of baicalein-producing engineered E. coli was rationally evaluated to enhanced the expression of key enzymes. Transcriptional analyses of baicalein-overproducing strain and a control strain enabled the identification of 13 beneficial genes, including 8 genes that are seemingly irrelevant to baicalein metabolism. With the combination of the enzyme assembly and modularization strategy, the engineered DN-8 strain produced 367.8 mg/L baicalein in fed-batch fermentation, the maximum titer reported to date. This article is protected by copyright. All rights reserved.

Dietary natural products as a potential inhibitor towards advanced glycation end products and hyperglycemic complications: A phytotherapy approaches

Natural products exist in various natural foods such as plants, herbs, fruits, and vegetables. Furthermore, marine life offers potential natural products with significant biological activity. The biochemical reaction is known as advanced glycation end products (AGEs) occurs in the human body. On the other hand, foods are capable of a wide range of processing conditions resulting in the generation of exogenous AGEs adducts. Protein glycation and the formation of advanced glycation end products both contribute to the pathogenesis of hyperglycemic complications. AGEs also play a pivotal role in microvascular and macrovascular complications progression by receptors for advanced glycation end products (RAGE). RAGE activate by AGEs leads to up-regulation of transcriptional factor NF-kB and inflammatory genes. Around the globe, researchers are working in various approaches for therapeutical implications on controlling AGEs mediated disease complications. In this regard, one of the potential promising agents observed with a wide range of AGEs inhibition by food-derived natural products. Current biotechnological tools have been turned to natural products or phytochemicals to manufacture the molecules without compromising their functionality. Metabolic engineering and bioinformatics perspectives have recently enabled the generation of a few potent metabolites with anti-diabetic activity. As the primary focus, this review article will also discuss multidisciplinary approaches that emphasize current advances in anti-diabetic therapeutic action and future perspectives of natural products.

Exploring phytochemicals from Himalayan medicinal plants as novel therapeutic agents

Over-prescription of medicines leads to some crucial health issues like resistance, non-specificity, etc. Therefore, a human consumes various natural foods, therapeutics, and nutritional supplements to combat this problem. Various therapeutic properties of secondary metabolites such as anticancer, anti-inflammatory, and antibacterial properties are important in drug discovery and medicinal application. These natural products has replaced synthetic materials, resulting in a great deal of sustainability, rational use and preservation of biodiversity. This review described the potential therapeutic applications of secondary plant metabolites found in Himalayan Indian plants. The database contains 45 plants to treat various diseases such as cancer, inflammation, and microbial infections. Besides authorized ITIS names, it includes Hindi names, family names, and active constituents. The most important information about the molecules can be found in the hyperlinks for the active constituents. It includes structures (two-dimensional and three-dimensional), names and identifiers, chemical and physical properties, spectral information, biochemistry, literature and patents. The review also references various phytochemicals responsible for preventing COVID-19. Despite several challenges in manufacturing natural products, researchers may conduct research to produce successful medicines with few side effects.

Recent advances in (chemo)enzymatic cascades for upgrading bio-based resources

Developing (chemo)enzymatic cascades is very attractive for green synthesis, because they streamline multistep synthetic processes. In this Feature Article, we have summarized the recent advances in in vitro or whole-cell cascade reactions with a focus on the use of renewable bio-based resources as starting materials. This includes the synthesis of rare sugars (such as ketoses, L-ribulose, D-tagatose, myo-inositol or aminosugars) from readily available carbohydrate sources (cellulose, hemi-cellulose, starch), in vitro enzyme pathways to convert glucose to various biochemicals, cascades to convert 5-hydroxymethylfurfural and furfural obtained from lignin or xylose into novel precursors for polymer synthesis, the syntheses of phenolic compounds, cascade syntheses of aliphatic and highly reduced chemicals from plant oils and fatty acids, upgrading of glycerol or ethanol as well as cascades to transform natural L-amino acids into high-value (chiral) compounds. In several examples these processes have demonstrated their efficiency with respect to high space-time yields and low E-factors enabling mature green chemistry processes. Also, the strengths and limitations are discussed and an outlook is provided for improving the existing and developing new cascades.

Recent trends in biocatalysis

Biocatalysis has undergone revolutionary progress in the past century. Benefited by the integration of multidisciplinary technologies, natural enzymatic reactions are constantly being explored. Protein engineering gives birth to robust biocatalysts that are widely used in industrial production. These research achievements have gradually constructed a network containing natural enzymatic synthesis pathways and artificially designed enzymatic cascades. Nowadays, the development of artificial intelligence, automation, and ultra-high-throughput technology provides infinite possibilities for the discovery of novel enzymes, enzymatic mechanisms and enzymatic cascades, and gradually complements the lack of remaining key steps in the pathway design of enzymatic total synthesis. Therefore, the research of biocatalysis is gradually moving towards the era of novel technology integration, intelligent manufacturing and enzymatic total synthesis.

Quercetin and Rutin as Modifiers of Aphid Probing Behavior

Rutin and its aglycone quercetin occur in the fruits, leaves, seeds, and grains of many plant species and are involved in plant herbivore interactions. We studied the effect of the exogenous application of rutin and quercetin on the probing behavior (= stylet penetration activities in plant tissues) of Acyrthosiphon pisum on Pisum sativum, Myzus persicae on Brassica rapa ssp. pekinensis, and Rhopalosiphum padi on Avena sativa using the electrical penetration graph technique (EPG = electropenetrography). The reaction of aphids to quercetin and rutin and the potency of the effect depended on aphid species, the flavonol, and flavonol concentration. Quercetin promoted probing activities of A. pisum within non-phloem and phloem tissues, which was demonstrated in the longer duration of probes and a trend toward longer duration of sap ingestion, respectively. M. persicae reached phloem in a shorter time on quercetin-treated B. rapa than on the control. Rutin caused a delay in reaching sieve elements by A. pisum and deterred probing activities of M. persicae within non-phloem tissues. Probing of R. padi was not affected by quercetin or rutin. The potency of behavioral effects increased as the applied concentrations of flavonols increased. The prospects of using quercetin and rutin in plant protection are discussed.

Improve the Biosynthesis of Baicalein and Scutellarein via Manufacturing Self-Assembly Enzyme Reactor In Vivo

Baicalein and scutellarein are bioactive flavonoids isolated from the traditional Chinese medicine Scutellaria baicalensis Georgi; however, there is a lack of effective strategies for producing baicalein and scutellarein. In this study, we developed a sequential self-assembly enzyme reactor involving two enzymes in the baicalein pathway with a pair of protein-peptide interactions in E. coli. These domains enabled us to optimize the stoichiometry of two baicalein biosynthetic enzymes recruited to be an enzymes complex. This strategy reduces the accumulation of intermediates and removes the pathway bottleneck. With this strategy, we successfully promoted the titer of baicalein by 6.6-fold (from 21.6 to 143.5 mg/L) and that of scutellarein by 1.4-fold (from 84.3 to 120.4 mg/L) in a flask fermentation, respectively. Furthermore, we first achieved the de novo biosynthesis of baicalein directly from glucose, and the strain was capable of producing 214.1 mg/L baicalein by fed-batch fermentation. This work provides novel insights for future optimization and large-scale fermentation of baicalein and scutellarein.

Native and non-native host assessment towards metabolic pathway reconstructions of plant natural products

•

Plant metabolic networks are highly complex.

•

Engineering the phytochemical pathways fully in heterologous hosts is challenging.

•

Single plant cells with amplified multiple fission enable homogeneity.

•

Homogeneity and high cell division rate can facilitate stable product scale-up.

Plant-based biopreparations are reasonably priced and are devoid of viral, prion and endotoxin contaminants. However, synthesizing these natural plant products by chemical methods is quite expensive. The structural complexity of plant-derived natural products poses a challenge for chemical synthesis at a commercial scale. Failure of commercial-scale synthesis is the chief reason why metabolic reconstructions in heterologous hosts are inevitable. This review discusses plant metabolite pathway reconstructions experimented in various heterologous hosts, and the inherent challenges involved. Plants as native hosts possess enhanced post-translational modification ability, along with rigorous gene edits, unlike microbes. To achieve a high yield of metabolites in plants, increased cell division rate is one of the requisites. This improved cell division rate will promote cellular homogeneity. Incorporation and maintenance of plant cell synchrony, in turn, can program stable product scale-up.

Advanced Strategies for the Synthesis of Terpenoids in Yarrowia lipolytica

Terpenoids are an important class of secondary metabolites that play an important role in food, agriculture, and other fields. Microorganisms are rapidly emerging as a promising source for the production of terpenoids. As an oleaginous yeast, Yarrowia lipolytica contains a high lipid content which indicates that it must produce high amounts of acetyl-CoA, a necessary precursor for the biosynthesis of terpenoids. Y. lipolytica has a complete eukaryotic mevalonic acid (MVA) pathway but it has not yet seen commercial use due to its low productivity. Several metabolic engineering strategies have been developed to improve the terpenoids production of Y. lipolytica, including developing the orthogonal pathway for terpenoid synthesis, increasing the catalytic efficiency of terpenoids synthases, enhancing the supply of acetyl-CoA and NADPH, expressing rate-limiting genes, and modifying the branched pathway. Moreover, most of the acetyl-CoA is used to produce lipid, so it is an effective strategy to strike a balance of precursor distribution by rewiring the lipid biosynthesis pathway. Lastly, the latest developed non-homologous end-joining strategy for improving terpenoid production is introduced. This review summarizes the status and metabolic engineering strategies of terpenoids biosynthesis in Y. lipolytica and proposes new insights to move the field forward.

Re-engineering Plant Phenylpropanoid Metabolism With the Aid of Synthetic Biosensors

Phenylpropanoids comprise a large class of specialized plant metabolites with many important applications, including pharmaceuticals, food nutrients, colorants, fragrances, and biofuels. Therefore, much effort has been devoted to manipulating their biosynthesis to produce high yields in a more controlled manner in microbial and plant systems. However, current strategies are prone to significant adverse effects due to pathway complexity, metabolic burden, and metabolite bioactivity, which still hinder the development of tailor-made phenylpropanoid biofactories. This gap could be addressed by the use of biosensors, which are molecular devices capable of sensing specific metabolites and triggering a desired response, as a way to sense the pathway's metabolic status and dynamically regulate its flux based on specific signals. Here, we provide a brief overview of current research on synthetic biology and metabolic engineering approaches to control phenylpropanoid synthesis and phenylpropanoid-related biosensors, advocating for the use of biosensors and genetic circuits as a step forward in plant synthetic biology to develop autonomously-controlled phenylpropanoid-producing plant biofactories.

Phytostilbenes as agrochemicals: biosynthesis, bioactivity, metabolic engineering and biotechnology

Covering: 1976 to 2020. Although constituting a limited chemical family, phytostilbenes represent an emblematic group of molecules among natural compounds. Ever since their discovery as antifungal compounds in plants and their ascribed role in human health and disease, phytostilbenes have never ceased to arouse interest for researchers, leading to a huge development of the literature in this field. Owing to this, the number of references to this class of compounds has reached the tens of thousands. The objective of this article is thus to offer an overview of the different aspects of these compounds through a large bibliography analysis of more than 500 articles. All the aspects regarding phytostilbenes will be covered including their chemistry and biochemistry, regulation of their biosynthesis, biological activities in plants, molecular engineering of stilbene pathways in plants and microbes as well as their biotechnological production by plant cell systems.

Discovery and Development of Inflammatory Inhibitors from 2-Phenylchromonone (Flavone) Scaffolds

Flavonoids are compounds based on a 2-phenylchromonone scaffold. Flavonoids can be divided into flavonoids, flavonols, dihydroflavones, anthocyanins, chalcones and diflavones according to the oxidation degree of the central tricarbonyl chain, the connection position of B-ring (2-or 3-position), and whether the tricarbonyl chain forms a ring or not. There are a variety of biological activities about flavonoids, such as anti-inflammatory activity, anti-oxidation and anti-tumor activity, and the antiinflammatory activity is apparent. This paper reviews the anti-inflammatory activities and mechanisms of flavonoids and their derivatives reported in China and abroad from 2011 till date (2011-2020), in order to find a good drug scaffold for the study of anti-inflammatory activities.

Promoter-Library-Based Pathway Optimization for Efficient (2S)-Naringenin Production from p-Coumaric Acid in Saccharomyces cerevisiae

Pathway optimization plays an important role in fine-tuning metabolic pathways. In most conditions, more than three genes are involved in the biosynthesis pathway of a specific target product. To improve the titer of products, rational regulation of a group of genes by a series of promoters with different strengths is essential. On the basis of a series of RNA-Seq data, a set of 66 native promoters was chosen to fine-tune gene expression in Saccharomyces cerevisiae. Promoter strength was characterized by measuring the fluorescence strength of the enhanced green fluorescent protein through fluorescence-activated cell sorting. The expressions of P_TDH1, P_PGK1, P_INO1, P_SED1, and P_CCW12 were stronger than that of P_TDH3, whereas those of another 15 promoters were stronger than that of P_TEF1. Then, 30 promoters were chosen to optimize the biosynthesis pathway of (2S)-naringenin from p-coumaric acid. With a high-throughput screening method, the highest titer of (2S)-naringenin in a 5 L bioreactor reached 1.21 g/L from p-coumaric acid, which is the highest titer according to the currently available reports.