Glycosyltransferases: managers of small molecules

Functional analysis of tandem glycosyltransferases catalyzing the O-glycosylation of flavonoid 4'-O-glycosyl-6-C-glycosides biosynthesis from Isatis indigotica

Flavonoid O-glycosyl-C-glycosides with promising biological activities including antitumor, antidiabetes, and antibacterials are the primary active ingredients of the medicinal plant Isatis indigotica's leaves. However, O-glycosyltransferases catalyzing flavonoid O-glycosyl-C-glycosides biosynthesis in I. indigotica's leaves remain unclear. In this study, guided by genome-wide investigation and phylogenetic analyses, 89 glycosyltransferases were obtained and clustered into 18 families. In vitro enzyme assays demonstrated that eight novel glycosyltransferases could catalyze the 4'-O-glycosylation of flavonoid 6-C-glycosides, and exhibited different catalytic properties. Moreover, tandem UGT73Bs, IiUGT15 and IiUGT16, could catalyze not only 4'-O-glycosylate flavonoid 6-C-glycosides such as isovitexin, isoorientin, and isoscoparin but also 7-O-glycosylate flavonoids, and hydrolyze the glucose moiety of flavonoid O-glycosides. Homology modeling and site-directed mutagenesis uncovered that the amino acids interacting with acceptors were highly conserved between IiUGT15 and IiUGT16, with various degreed effects on 4'-O-glycosylation, potentially leading to differences in their catalytic activity. Isoorientin-4'-O-β-D-glucoside was synthesized in Escherichia coli without the exogenous supplementation of UDP-glucose. Overall, this study offered new biocatalysts to attain 4'-O-glycosylation of flavonoid C-glycosides for drug discovery and established a foundation for the biomanufacturing of critical flavonoid O-glycosyl-C-glycosides.

Glycosyltransferases: Pioneering roles in agriculture and medicine

Glycosyltransferases (GTs) belong to a diverse family of enzymes that catalyze the transfer of sugar moieties from activated donor sugars to specific acceptors, thus playing a crucial roles in various biological processes. This review explores the pioneering roles of uridine diphosphate-dependent GTs (UGTs), which use uridine diphosphate glucose as donors. UGTs have also been extensively studied in agricultural and medical fields, emphasizing their potential to revolutionize these sectors. In the agricultural sector, the genetic engineering of UGTs has demonstrate potential in developing crops with enhanced stress tolerance, regulated plant development, and increased resistance to pests and diseases. These advancements not only contribute to sustainable farming practices but also address global food security challenges by facilitating the production of more resilient plant varieties. Furthermore, UGTs facilitate the synthesis of complex carbohydrates and glycoconjugates in plants, which are critical for developing drugs and therapeutic strategies targeting various ailments, including cancer and infectious diseases. Thus, this review explored the functions and synthesis methods of flavonoid glycosides, terpenoid glycosides, and polyketosides in detail. Moreover, owing to the functional diversity of UGTs, numerous research methods were reviewed, and novel, more valuable UGTs will be obtained. In summary, this study synthesizes the current research findings and discusses future perspectives to underscore the transgenic technology and synthetic biological impact of UGTs on agriculture and medicine and bridge the gap between fundamental science and practical applications.

The activity annotation of peach glycosyltransferase PpUGT78B based on engineering bacterial anthocyanin biosynthesis

Glycosylation modification allows the formation of anthocyanin from anthocyanidin, which enhances the stability of anthocyanins and improves fruit coloration and anthocyanin availability as a human functional component. Flavonoid glycosyltransferases (UFGT) are responsible for catalyzing anthocyanidin glycosylation. In the present study, to better clarify peach (Prunus persica L.) UFGT (PpUGT78B) function, an engineering bacterial system was constructed, which used the anthocyanidin synthase (ANS) gene for producing cyanidin with the incorporation of (+)-catechin precursors and further synthesized cyanidin-3-O-glucoside (C3G) with UFGT co-expression. In addition, it was found that expression of fusion proteins with ANS and UFGT could improve C3G production by about 15 %-20 % in engineering bacterial systems. Furthermore, combining the molecular modeling prediction and targeted mutagenesis, this engineering bacterial system linked some residues in PpUGT78B to glycosylation capacity, which involved F210, L148, Q393, G391, and H230, whose mutation resulted in reduced enzyme activity or even loss and also involved F203 and S29 whose mutation resulted in the increased catalytic activity. Subsequently, a natural mutation of PpUGT78B was detected by analyzing 109 peach genome re-sequencing data, and two residue mutants (E82D, V276F) were found in two peach varieties. Further, these two natural mutation sites were confirmed to reduce PpUGT78B activity in engineering bacterial systems. This study demonstrates the effectiveness of the engineering bacteria system in anthocyanin biosynthesis. It offers valuable insights into the functional and structural roles of PpUGT78B, advancing our understanding of anthocyanin glycosylation.

Buckwheat UDP-Glycosyltransferase FtUGT71K6 and FtUGT71K7 Tandem Repeats Contribute to Drought Tolerance by Regulating Epicatechin Synthesis

Glycosyltransferase genes are organised as tandem repeats in the buckwheat genome, yet the functional implications and evolutionary significance of duplicated genes remain largely unexplored. In this study, gene family analysis revealed that FtUGT71K6 and FtUGT71K7 are tandem repeats in the buckwheat genome. Moreover, GWAS results for epicatechin suggested that this tandem repeat function was associated with epicatechin content of Tartary buckwheat germplasm, highlighting variations in the promoter haplotypes of FtUGT71K7 influenced epicatechin levels. FtUGT71K6 and FtUGT71K7 were shown to catalyse UDP-glucose conjugation to cyanidin and epicatechin. Furthermore, overexpression of FtUGT71K6 and FtUGT71K7 increased total antioxidant capacity and altered metabolite content of the epicatechin biosynthesis pathway, contributing to improved drought tolerance, while overexpression of FtUGT71K6 significantly improved salt stress tolerance. However, overexpression of these two genes did not contribute to resistance against Rhizoctonia solani. Evolutionary selection pressure analysis suggested positive selection of a critical amino acid ASP-53 in FtUGT71K6 and FtUGT71K7 during the duplication event. Overall, our study indicated that FtUGT71K6 and FtUGT71K7 play crucial roles in drought stress tolerance via modulating epicatechin synthesis in buckwheat.

The Glycosylation Status of Small Molecules Impacts Different Aspects of Plant Immunity

Plants, as sessile organisms, are constantly exposed to biotic stresses and have evolved intricate defense mechanisms to survive. Small molecules, including hormones, novel signaling compounds, and secondary metabolites, play pivotal roles in plant immunity. UDP-glycosyltransferases (UGTs) and family 1 glycoside hydrolases (GH1 β-glycosidases) are key enzymes that regulate the glycosylation and deglycosylation of these small molecules. Through the addition or removal of sugar moieties, these enzymes modulate the biological properties and functions of defense-related hormones, signaling compounds, and secondary metabolites. Extensive research has elucidated the substrates of UGTs and GH1 β-glycosidases and their roles in regulating the glycosylation status of small molecules, which is critical for various layers of plant immunity. This review explores the contributions of UGTs and GH1 β-glycosidases in: (1) the primary defense layer, including physical barriers and chemical defenses; (2) modifying small signaling molecules to enhance disease resistance; and (3) mediating interactions between the root microbiome and plant immune responses. Understanding the dynamic regulation of glycosylation in plant immunity is essential for advancing our knowledge of plant defense mechanisms.

Sustainable and Scalable Enzymatic Production, Structural Elucidation, And Biological Evaluation of Novel Phlorizin Analogues

It is not unusual for naturally occurring compounds to be limited for their use in cosmetics due to their low water solubility. Recently, aiming at accessing novel phlorizin (a glycosylated bioactive recovered from apple tree wood and already used in cosmetics as antioxidant ingredient) analogues, we reported the synthesis of very promising - but low water-soluble - biomass-derived chalcones (CHs) and dihydrochalcones (DHCs) exhibiting antioxidant and anti-tyrosinase activities. Glycosylating bioactive compounds being one of the most common strategies to increase their water solubility, herein we report the enzymatic glycosylation of the CHs mentioned above, as well as DHC using cyclodextrin glycosyltransferases (CGTase), enzymes well-known for catalyzing the selective α(1→4) transglycosylation. Indeed, while most natural glycosides are β-glycosides (such as phlorizin), the selected enzyme produces selectively new α-glycosides, thus expanding their structural diversity. A first step of separation using Centrifugal Partition Chromatography (CPC) led to mono-, di- or triglycosides-enriched fractions, which were then submitted to a comprehensive purification strategy for an in-depth chemical profiling of the synthesized α-glycosides, revealing that the major compounds were glycosylpyranosides. Surprisingly, among the diglycosides characterized, besides the expected maltoside compounds, nigeroside derivatives were also identified in significant amounts, depending on the starting compound structure. Finally, evaluating the antiradical, anti-tyrosinase and antimicrobial activities of the major glycosides revealed them as potential sustainable alternatives to current petro-sourced cosmetic ingredients.

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.

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

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

Rice glycosyltransferase UGT706F1 functions in heat tolerance through glycosylating flavonoids under the regulation of transcription factor MYB61

Global metabolic and transcriptional reprogramming is a common event in plant abiotic stress responses, however, the relevant molecular mechanisms remain largely unknown. Here, we characterized the physiological function and molecular mechanism for the rice UGT706F1. We found that UGT706F1 can be potently induced by high temperature. Its overexpression can markedly enhance the heat tolerance of rice through improving the capacity of scavenging reactive oxygen species, whereas its functional deletion results in heat sensitivity in rice. To investigate the regulatory mechanism of UGT706F1 in response to high temperature, we carried out extensive screening of the in vitro enzymatic activity of UGT706F1 and discovered that UGT706F1 exhibits broad-spectrum activity toward flavonoid compounds. Through targeted flavonoid metabolomics analysis, we further revealed that the overexpression of UGT706F1 elevated the content of diverse flavonoids and flavonoid glycosides in rice. Subsequently, via transcriptome analysis, we found that following heat treatment, the overexpression of UGT706F1 was capable of enhancing the transcriptional activity of those genes including the flavonoid synthases, heat shock factors, heat shock proteins, glutathione S-transferase, and various antioxidant enzymes. Furthermore, we identified an R2R3 MYB-type transcription factor MYB61 and demonstrated that MYB61 could directly bind the promoter of UGT706F1 and activate the transcription of UGT706F1. The overexpression of MYB61 also enhanced the heat tolerance and increased flavonoid glycosides. Overall, this study unveiled a novel pathway of the plant heat tolerance response mediated by MYB61-UGT706F1 module and identified a new UGT player for the metabolic and transcriptional regulation under high-temperature circumstance.

Enhanced Cellobiose Production from Cellulose by CaCl2-Phosphoric Acid Pretreatment for the Efficient Preparation of Astragalin in Recombinant Escherichia coli

Cellulose, as the most abundant and cheap renewable resource in nature, is of great importance for its utilization. An enzymatic cellulose solution, mainly containing cellobiose and glucose, was utilized to produce astragalin instead of cellobiose in the recombinant strains. However, the crystalline structure of cellulose affects the production of cellobiose, resulting in a low astragalin yield. In this study, microcrystalline cellulose was pretreated with phosphoric acid and CaCl2 to enhance the hydrolysis yield of cellobiose. By pretreating with CaCl2-phosphoric acid, the crystallinity of cellulose significantly decreases, while the specific surface area increases, which leads to a significant increase in the production of cellobiose. When cellulose was treated with CaCl2-phosphoric acid at 50 °C and hydrolyzed with 30 FPU/g cellulose, the maximum cellobiose production with yeast extract added reached 1.60 g/L, which was 200% of the control. The maximal astragalin production reached 2038.3 mg/L with the cellulose enzymatic solution. Finally, 100 g of cellulose can produce 34.67 g of glucose and 26.67 g of cellobiose. The recombinant strains produced a total of 25 g of astragalin from these sugars, which is 322% of that from the untreated cellulose. This work provides an economical and efficient method for the production of astragalin.

Arabidopsis glycosyltransferase UGT86A1 promotes plant adaptation to salt and drought stresses

UDP-glycosyltransferases (UGTs) are the largest glycosyltransferase family developed during the evolution of the plant kingdom. However, their physiological significance in abiotic stress adaptation in land plants is largely unknown. In this study, we identified a UGT gene from Arabidopsis thaliana, UGT86A1, that was significantly induced by salt and drought stresses. To explore the potential biological role of UGT86A1 in salt and drought stress response, we created ugt86a1 knockout mutants and UGT86A1-overexpressing transgenic lines, and analyzed seed germination, seedling development and root growth. The results showed that ugt86a1 mutants are sensitive to drought and salt stresses, while overexpression lines show stronger resistance compared with WT, confirming the positive regulation role of UGT86A1 in abiotic stress response. Our following study indicated that UGT86A1 enhances plant resistance against salt and drought stresses via increasing soluble sugar concentration and promoting ROS scavenging capacity, thereby reducing the damage to plant organs and cells. Moreover, we identified that UGT86A1 largely contributes to the upregulation of multiple stress-induced genes under salt and drought stress conditions. Therefore, our results demonstrated that UGT86A1 is a crucial responsive gene to salt and drought stresses in a land plant, thus promoting the understanding of the physiological significance of the UGT family in plant evolution.

Evolution and functional divergence of glycosyltransferase genes shaped the quality and cold tolerance of tea plants

Plant uridine diphosphate-dependent glycosyltransferases (UGTs) play a key role in plant growth and metabolism. Here, we examined the evolutionary landscape among UGTs in 28 fully sequenced species from early algae to angiosperms. Our findings revealed a distinctive expansion and contraction of UGTs in the G and H groups in tea (Camellia sinensis), respectively. Whole-genome duplication and tandem duplication events jointly drove the massive expansion of UGTs, and the interplay of natural and artificial selection has resulted in marked functional divergence within the G group of the sinensis-type tea population. In Cluster II of group G, differences in substrate selection (e.g. abscisic acid) of the enzymes encoded by UGT genes led to their functional diversification, and these genes influence tolerance to abiotic stresses such as low temperature and drought via different modes of positive and negative regulation, respectively. UGTs in Cluster III of the G group have diverse aroma substrate preferences, which contribute a diverse aroma spectrum of the sinensis-type tea population. All Cluster III genes respond to low-temperature stress, whereas UGTs within Cluster III-1, shaped by artificial selection, are unresponsive to drought. This suggests that artificial selection of tea plants focused on improving quality and cold tolerance as primary targets.

Genome-wide characterization of Solanum tuberosum UGT gene family and functional analysis of StUGT178 in salt tolerance

UDP-glycosyltransferases (UGTs) widely exist in plants and play essential roles in catalyzing the glycosylation reaction associated with metabolic processes. UGT gene family has been identified in many species to date. However, the comprehensive identification and systematic analysis have not been documented yet in the latest potato genome. In this study, a total of 295 UGT members (StUGT) were identified and found to be unevenly distributed on twelve chromosomes of potato. All StUGT genes were classified into 17 groups (A-P, R) and the UGT genes within the same groups have similar structural characterization. Tandem duplication was the major driving force for the StUGT gene expansion. The prediction of cis-acting elements showed that the development process, light, phytohormone, and abiotic stress-responsive elements generally existed in StUGT promoter regions. Analysis of spatial and temporal expression patterns demonstrated that StUGT genes were widely and differentially expressed in various tissues. Additionally, to investigate the salt stress-responsive genes, we analyzed the expression profiles of the StUGT genes under salt treatment. A total of 50 and 20 StUGT genes were continuously up- and down-regulated, respectively, implicating that these genes were involved in the regulation of salt tolerance. Among them, the StUGT178 gene, which was significantly induced by salt stress and contains salt-responsive element, was considered as one of the most relevant candidate genes. Transient transformation of the StUGT178 promoter in tobacco revealed that the transcriptional activation activity of the StUGT178 gene was strengthened under salt treatment. Furthermore, the heterologous expressions of the promoter and coding protein of the StUGT178 gene in Arabidopsis further demonstrated that the StUGT178 gene significantly responds to salt treatment, and enhanced salinity tolerance by regulating antioxidant enzyme activity and H2O2 accumulation. These results provide comprehensive information for a better understanding of the StUGT genes and offer a foundation for uncovering their function associated with salt stress in potato.

Genome-Wide Association Study on Cowpea seed coat color using RGB images

This study delves into the genetic mechanisms underlying seed coat color variation in cowpeas (Vigna unguiculata [L.] Walp.), a trait with significant implications for nutritional value, consumer preference, and adaptation to environmental stresses. Through a genome-wide association study (GWAS) involving cowpea accessions exhibiting red, green, and blue seed coats, we identified 16 significant single nucleotide polymorphisms (SNPs) distributed across chromosomes 3, 4, 5, 9, 10, and 11. Our analysis highlighted the polygenic nature of seed coat color, emphasizing the shared SNP loci across different colors, suggesting integrated genetic influence or linked inheritance patterns, especially on chromosomes 9 and 10. We highlighted candidate genes, including Pentatricopeptide repeat family (PPR), Lupus La-related protein/La-related protein 1, and Udp-glycosyltransferase 71b2-related genes on chromosome 9, and MYB-like DNA-binding (MYB) genes on chromosome 10, all of which are implicated in pigment biosynthesis and regulatory pathways crucial to seed coat coloration and plant physiological processes. Our results corroborate previous findings linking seed coat color to the anthocyanin biosynthesis pathway and reveal the complex genetic architecture and phenotypic plasticity inherent in cowpeas. The overlap in quantitative trait loci (QTL) regions across different seed coat colors points to a shared genetic basis, potentially enabling the manipulation of seed coat color to enhance the nutritional profile and marketability of cowpeas.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11032-024-01516-2.

CsUGT95B11 glycosylates quercetin to enhance resistance of tea plant (Camellia sinensis) to Ectropis grisescens

Herbivore attack is a major type of biotic stress that greatly affects the development and quality of tea plant [Camellia sinensis (L) O. Kuntze]. Tea plant produces many glycosylated compounds that enhance resistance to herbivores. An example is quercetin, one of the major flavonols of tea plants, which was glycosylated to involve responses to various environmental stresses. However, not much is known about the biosynthesis of glycosylated quercetin derivatives in tea plant in response to herbivorous attack. Here, we found that E. grisescens attack significantly increased the contents of quercetin 3-O-glucoside and quercetin 7-O-glucoside in tea leaves, and exogenous application of these two compounds improved the E. grisescens resistance of tea plant. Integrated transcriptome and phylogenetic analyses identified CsUGT95B11 gene, encoding a quercetin glycosyltransferase, which was upregulated in response to E. grisescens attack. Enzymatic assays showed that CsUGT95B11 preferentially glycosylated quercetin to produce quercetin 7-O-glucoside with a kcat·Km-1 value of 9655.52 M-1 s-1. Subcellular localization analysis indicated that CsUGT95B11 was dispersed in the cytoplasm of Nicotiana benthamiana leaves and Arabidopsis protoplast. Suppression of CsUGT95B11 reduced the quercetin glucoside content of tea leaves and impaired resistance of tea plant to E. grisescens. These results indicate that CsUGT95B11 is a quercetin glycosyltransferase that enhances resistance of tea plant to E. grisescens, providing insights into the mechanism of flavonol glycosylation regulating interactions between plants and herbivores.

Chemical and Transcriptomic Analyses Provide New Insights into Key Genes for Ginsenoside Biosynthesis in the Rhizome of Panax japonicus C. A. Meyer

Panax japonicus C. A. Meyer is renowned for its significant therapeutic effects and is commonly used worldwide. Its active ingredients, triterpenoid saponins, show variation in content among different tissues. The tissue-specific distribution of saponins is potentially related to the expression of vital genes in the biosynthesis pathway. In this study, the contents of five saponins (ginsenoside Ro, chikusetsusaponin IV, chikusetsusaponin IVa, ginsenoside Rg1, and ginsenoside Rb1) in three different tissues were determined by HPLC. Transcriptome sequencing analysis identified differentially expressed genes (DEGs) involved in triterpenoid saponin biosynthesis, highlighting significant correlations between saponin contents and the expression levels of 10 cytochrome p450 monooxygenase (CYP) and 3 UDP-glycosyltransferase (UGT) genes. Cloning, sequencing, and prokaryotic expression of UGT genes confirmed the molecular weights of UGT proteins. Gene sequence alignment and phylogenetic analysis provided preliminary insights into UGT gene functions. Meanwhile, the function of one UGT gene was characterized in the yeast. These findings advance our understanding of the triterpenoid saponin biosynthesis in P. japonicus and support future research in traditional Chinese medicine (TCM) and synthetic biology.

Production of cinnamates and benzoates glucose esters by bioconversion using Escherichia coli expressing a glucosyltransferase from sweet potato

Sweet potatoes (Ipomoea batatas) produce glucose esters from cinnamates during stress responses. We isolated a glucosyltransferase, IbGT1 (UGT84A20), from sweet potato and characterized its recombinant enzyme heterologously expressed in Escherichia coli. The recombinant IbGT1 enzyme reacted with cinnamates, especially p-coumaric acid, ferulic acid, and sinapic acid, and showed activity against benzoates with an optimum pH of 5.0-5.5. The enzyme also reacted with flavonoids under alkaline conditions (pH 8.0), with the main product being 7-O-glucosides. Bioconversion using E. coli expressing IbGT1 (Ec-IbGT1) as a whole cell biocatalyst converted 200 µM cinnamates such as p-coumaric acid and benzoates such as p-hydroxybenzoic acid into their glucose esters mostly within 3-6 h. The conversion rates for caffeic acid and sinapic acid were much lower than those for the other substrates tested, which took more than 6 h, despite the enzymatic activities of IbGT1 against these compounds being comparable to the others. Scaled-up production combined with repeated administration of sinapic acid, trans-cinnamic acid and p-hydroxybenzoic acid at a concentration of 200 µM yielded their glucose esters with conversion rates of 74-95% in 20-30 h. These results suggest that the Ec-IbGT1 system efficiently produces these glucose esters.

Insights from Structure-Based Simulations into the Persulfidation of Uridine Diphosphate-Glycosyltransferase71c5 Facilitating the Reversible Inactivation of Abscisic Acid

The action of abscisic acid (ABA) is closely related to its level in plant tissues. Uridine diphosphate-glycosyltransferase71c5 (UGT71C5) was characterized as a major UGT enzyme to catalyze the formation of the ABA-glucose ester (ABA-GE), a reversible inactive form of free ABA in Arabidopsis thaliana (thale cress). UGTs function in a mode where the catalytic base deprotonates an acceptor to allow a nucleophilic attack at the anomeric center of the donor, achieving the transfer of a glucose moiety. The proteomic data revealed that UGT71C5 can be persulfidated. Herein, an experimental method was employed to detect the persulfidation site of UGT71C5, and the computational methods were further used to identify the yet unknown molecular basis of ABA glycosylation as well as the regulatory role of persulfidation in this process. Our results suggest that the linker and the U-shaped loop are regulatory structural elements: the linker is associated with the binding of uridine diphosphate glucose (UPG) and the U-shaped loop is involved in binding both UPG and ABA.It was also found that it is through tuning the dynamics of the U-shaped loop that is accompanied by the movement of tyrosine (Y388) that the persulfidation of cysteine (C311) leads to the catalytic residue histidine (H16) being in place, preparing for the deprotonation of ABA, and then reorientates UPG and deprotonated ABA closer to the 'Michaelis' complex, facilitating the transfer of a glucose moiety. Ultimately, the persulfidation of UGT71C5 is in favor of ABA glycosylation. Our results provide insights into the molecular details of UGT71C5 recognizing substrates and insights concerning persulfidation as a possible mechanism for hydrogen sulfide (H2S) to modulate the content of ABA, which helps us understand how modulating ABA level strengthens plant tolerance.

Uridine diphosphate (UDP)-glycosyltransferases (UGTs) are associated with insecticide resistance in the major malaria vectors Anopheles gambiae s.l. and Anopheles funestus

Malaria remains one of the highest causes of morbidity and mortality, with 249 million cases and over 608,000 deaths in 2022. Insecticides, which target the Anopheles mosquito vector, are the primary method to control malaria. The widespread nature of resistance to the most important insecticide class, the pyrethroids, threatens the control of this disease. To reverse the stall in malaria control there is urgent need for new vector control tools, which necessitates understanding the molecular basis of pyrethroid resistance. In this study we utilised multi-omics data to identify uridine-diphosphate (UDP)-glycosyltransferases (UGTs) potentially involved in resistance across multiple Anopheles species. Phylogenetic analysis identifies sequence similarities between Anopheline UGTs and those involved in agricultural pesticide resistance to pyrethroids, pyrroles and spinosyns. Expression of five UGTs was characterised in An. gambiae and An. coluzzii to determine constitutive over-expression, induction, and tissue specificity. Furthermore, a UGT inhibitor, sulfinpyrazone, restored susceptibility to pyrethroids and DDT in An. gambiae, An. coluzzii, An. arabiensis and An. funestus, the major African malaria vectors. Taken together, this study provides clear association of UGTs with pyrethroid resistance as well as highlighting the potential use of sulfinpyrazone as a novel synergist for vector control.

Enzymatic glycosylation of aloesone performed by plant UDP-dependent glycosyltransferases

Aloesone is a bioactive natural product and biosynthetic precursor of rare glucosides found in rhubarb and some aloe plants including Aloe vera. This study aimed to investigate biocatalytic aloesone glycosylation and more than 400 uridine diphosphate-dependent glycosyltransferase (UGT) candidates, including multifunctional and promiscuous enzymes from a variety of plant species were assayed. As a result, 137 selective aloesone UGTs were discovered, including four from the natural producer rhubarb. Rhubarb UGT72B49 was further studied and its catalytic constants (kcat = 0.00092 ± 0.00003 s-1, KM = 30 ± 2.5 μM) as well as temperature and pH optima (50 °C and pH 7, respectively) were determined. We further aimed to find an efficient aloesone glycosylating enzyme with potential application for biocatalytic production of the glucoside. We discovered UGT71C1 from Arabidopsis thaliana as an efficient aloesone UGT showing a 167-fold higher catalytic efficiency compared to that of UGT72B49. Interestingly, sequence analysis of all the 137 newly identified aloesone UGTs showed that they belong to different phylogenetic groups, with the highest representation in groups B, D, E, F and L. Finally, our study indicates that aloesone C-glycosylation is highly specific and rare, since it was not possible to achieve in an efficient manner with any of the 422 UGTs assayed, including multifunctional GTs and 28 known C-UGTs.

Integrated Metabolomics and Transcriptomics Reveal the Key Role of Flavonoids in the Cold Tolerance of Chrysanthemum

Chrysanthemum (Chrysanthemum morifolium, ground-cover Chrysanthemums), one of the important garden flowers, has a high ornamental and economic value. However, its ornamental value is significantly diminished by the low temperature experienced in northeastern China. Here, metabolomics and transcriptomics were performed on three Chrysanthemum cultivars before and after a low temperature to investigate the dynamic metabolite changes and the molecular regulatory mechanisms. The results showed that 1324 annotated metabolites were detected, among which 327 were identified as flavonoids derived from Chrysanthemum. The accumulation of metabolites and gene expression related to the flavonoid biosynthesis pathway significantly increased in the three cultivars under the low temperature, indicating flavonoid metabolism actively participates in the Chrysanthemum cold response. Specifically, the content of cyanidin and pelargonidin derivatives and the expression of anthocyanin biosynthesis genes significantly increases in XHBF, providing a reasonable explanation for the change in petal color from white to purple under the low temperature. Six candidate UDP-glycosyltransferase genes involved in the glycosylation of flavonoids were identified through correlation networks and phylogenetic analysis. CmNAC1, CmbZIP3, and other transcription factors potentially regulating flavonoid metabolism and responding to low temperatures were discovered by correlation analysis and weighted gene co-expression network analysis (WGCNA). In conclusion, this study elucidated the specific response of flavonoids to low temperatures in Chrysanthemums, providing valuable insights and metabolic data for investigating cold tolerance.

GASP: A Pan-Specific Predictor of Family 1 Glycosyltransferase Acceptor Specificity Enabled by a Pipeline for Substrate Feature Generation and Large-Scale Experimental Screening

Glycosylation represents a major chemical challenge; while it is one of the most common reactions in Nature, conventional chemistry struggles with stereochemistry, regioselectivity, and solubility issues. In contrast, family 1 glycosyltransferase (GT1) enzymes can glycosylate virtually any given nucleophilic group with perfect control over stereochemistry and regioselectivity. However, the appropriate catalyst for a given reaction needs to be identified among the tens of thousands of available sequences. Here, we present the glycosyltransferase acceptor specificity predictor (GASP) model, a data-driven approach to the identification of reactive GT1:acceptor pairs. We trained a random forest-based acceptor predictor on literature data and validated it on independent in-house generated data on 1001 GT1:acceptor pairs, obtaining an AUROC of 0.79 and a balanced accuracy of 72%. The performance was stable even in the case of completely new GT1s and acceptors not present in the training data set, highlighting the pan-specificity of GASP. Moreover, the model is capable of parsing all known GT1 sequences, as well as all chemicals, the latter through a pipeline for the generation of 153 chemical features for a given molecule taking the CID or SMILES as input (freely available at https://github.com/degnbol/GASP). To investigate the power of GASP, the model prediction probability scores were compared to GT1 substrate conversion yields from a newly published data set, with the top 50% of GASP predictions corresponding to reactions with >50% synthetic yields. The model was also tested in two comparative case studies: glycosylation of the antihelminth drug niclosamide and the plant defensive compound DIBOA. In the first study, the model achieved an 83% hit rate, outperforming a hit rate of 53% from a random selection assay. In the second case study, the hit rate of GASP was 50%, and while being lower than the hit rate of 83% using expert-selected enzymes, it provides a reasonable performance for the cases when an expert opinion is unavailable. The hierarchal importance of the generated chemical features was investigated by negative feature selection, revealing properties related to cyclization and atom hybridization status to be the most important characteristics for accurate prediction. Our study provides a GT1:acceptor predictor which can be trained on other data sets enabled by the automated feature generation pipelines. We also release the new in-house generated data set used for testing of GASP to facilitate the future development of GT1 activity predictors and their robust benchmarking.

Rational Design for the Complete Synthesis of Stevioside in Saccharomyces cerevisiae

Stevioside is a secondary metabolite of diterpenoid glycoside production in plants. It has been used as a natural sweetener in various foods because of its high sweetness and low-calorie content. In this study, we constructed a Saccharomyces cerevisiae strain for the complete synthesis of stevioside using a metabolic engineering strategy. Firstly, the synthesis pathway of steviol was modularly constructed in S. cerevisiae BY4742, and the precursor pathway was strengthened. The yield of steviol was used as an indicator to investigate the expression effect of different sources of diterpene synthases under different combinations, and the strains with further improved steviol yield were screened. Secondly, glycosyltransferases were heterologously expressed in this strain to produce stevioside, the sequence of glycosyltransferase expression was optimized, and the uridine diphosphate-glucose (UDP-Glc) supply was enhanced. Finally, the results showed that the strain SST-302III-ST2 produced 164.89 mg/L of stevioside in a shake flask experiment, and the yield of stevioside reached 1104.49 mg/L in an experiment employing a 10 L bioreactor with batch feeding, which was the highest yield reported. We constructed strains with a high production of stevioside, thus laying the foundation for the production of other classes of steviol glycosides and holding good prospects for application and promotion.

Functional Characterization of F3H Gene and Optimization of Dihydrokaempferol Biosynthesis in Saccharomyces cerevisiae

The 1092 bp F3H gene from Trapa bispinosa Roxb., which was named TbF3H, was cloned and it encodes 363 amino acids. Bioinformatic and phylogenetic tree analyses revealed the high homology of TbF3H with flavanone 3-hydroxylase from other plants. A functional analysis showed that TbF3H of Trapa bispinosa Roxb. encoded a functional flavanone 3-hydroxylase; it catalyzed the formation of dihydrokaempferol (DHK) from naringenin in S. cerevisiae. The promoter strengths were compared by fluorescence microscopy and flow cytometry detection of the fluorescence intensity of the reporter genes initiated by each constitutive promoter (FITC), and DHK production reached 216.7 mg/L by the promoter adjustment strategy and the optimization of fermentation conditions. The results presented in this study will contribute to elucidating DHK biosynthesis in Trapa bispinosa Roxb.

Analysis of drought and heat stress response genes in rice using co-expression network and differentially expressed gene analyses

Studies on Oryza sativa (rice) are crucial for improving agricultural productivity and ensuring global sustenance security, especially considering the increasing drought and heat stress caused by extreme climate change. Currently, the genes and mechanisms underlying drought and heat resistance in rice are not fully understood, and the scope for enhancing the development of new strains remains considerable. To accurately identify the key genes related to drought and heat stress responses in rice, multiple datasets from the Gene Expression Omnibus (GEO) database were integrated in this study. A co-expression network was constructed using a Weighted Correlation Network Analysis (WGCNA) algorithm. We further distinguished the core network and intersected it with differentially expressed genes and multiple expression datasets for screening. Differences in gene expression levels were verified using quantitative real-time polymerase chain reaction (PCR). OsDjC53, MBF1C, BAG6, HSP23.2, and HSP21.9 were found to be associated with the heat stress response, and it is also possible that UGT83A1 and OsCPn60a1, although not directly related, are affected by drought stress. This study offers significant insights into the molecular mechanisms underlying stress responses in rice, which could promote the development of stress-tolerant rice breeds.

Unraveling the enigma: housekeeping gene Ugt1a7c as a universal biomarker for microglia

Background

Microglia, brain resident macrophages, play multiple roles in maintaining homeostasis, including immunity, surveillance, and protecting the central nervous system through their distinct activation processes. Identifying all types of microglia-driven populations is crucial due to the presence of various phenotypes that differ based on developmental stages or activation states. During embryonic development, the E8.5 yolk sac contains erythromyeloid progenitors that go through different growth phases, eventually resulting in the formation of microglia. In addition, microglia are present in neurological diseases as a diverse population. So far, no individual biomarker for microglia has been discovered that can accurately identify and monitor their development and attributes.

Summary

Here, we highlight the newly defined biomarker of mouse microglia, UGT1A7C, which exhibits superior stability in expression during microglia development and activation compared to other known microglia biomarkers. The UGT1A7C sensing chemical probe labels all microglia in the 3xTG AD mouse model. The expression of Ugt1a7c is stable during development, with only a 4-fold variation, while other microglia biomarkers, such as Csf1r and Cx3cr1, exhibit at least a 10-fold difference. The UGT1A7C expression remains constant throughout its lifespan. In addition, the expression and activity of UGT1A7C are the same in response to different types of inflammatory activators' treatment in vitro.

Conclusion

We propose employing UGT1A7C as the representative biomarker for microglia, irrespective of their developmental state, age, or activation status. Using UGT1A7C can reduce the requirement for using multiple biomarkers, enhance the precision of microglia analysis, and even be utilized as a standard for gene/protein expression.

Identification of two 6'-deoxychalcone 4'-glucosyltransferase genes in dahlia (Dahlia variabilis)

MAIN CONCLUSION

Two glycosyltransferase genes belonging to UGT88 family were identified to have 6'-deoxychalcone 4'-glucosyltransferase activity in dahlia. 6'-Deoxychalcones (isoliquiritigenin and butein) are important pigments for yellow and orange to red flower color. 6'-Deoxychalcones are glucosylated at the 4'-position in vivo, but the genes encoding 6'-deoxychalcone 4'-glucosyltransferase have not yet been identified. In our previous study, it was indicated that snapdragon (Antirrhinum majus) chalcone 4'-O-glucosyltransferase (Am4'CGT) has isoliquiritigenin 4'-glucosylation activity. Therefore, to identify genes encoding 6'-deoxychalcone 4'-glucosyltransferase in dahlia (Dahlia variabilis), genes expressed in ray florets that shared high homology with Am4'CGT were explored. As a result, c34671_g1_i1 and c35662_g1_i1 were selected as candidate genes for 6'-deoxychalcone 4'-glucosyltransferases in dahlia. We conducted transient co-overexpression of three genes (c34671_g1_i1 or c35662_g1_i1, dahlia aldo-keto reductase1 (DvAKR1) or soybean (Glycine max) chalcone reductase5 (GmCHR5), and chili pepper (Capsicum annuum) MYB transcription factor (CaMYBA)) in Nicotiana benthamiana by agroinfiltration. Transient overexpression of c34671_g1_i1, DvAKR1, and CaMYBA resulted in increase in the accumulation of isoliquiritigenin 4'-glucosides, isoliquiritigenin 4'-O-glucoside, and isoliquiritigenin 4'-O-[6-O-(malonyl)-glucoside]. However, transient overexpression of c35662_g1_i1, DvAKR1, and CaMYBA did not increase accumulation of isoliquiritigenin 4'-glucosides. Using GmCHR5 instead of DvAKR1 showed similar results suggesting that c34671_g1_i1 has isoliquiritigenin 4'-glucosyltransferase activity. In addition, we conducted co-overexpression of four genes (c34671_g1_i1, c35662_g1_i1 or Am4'CGT, DvAKR1 or GmCHR5, CaMYBA, and chalcone 3-hydroxylase from dahlia). Accumulation of butein 4'-O-glucoside and butein 4'-O-[6-O-(malonyl)-glucoside] was detected for c35662_g1_i1, suggesting that c35662_g1_i1 has butein 4'-glucosyltransferase activity. Recombinant enzyme analysis also supported butein 4'-glucosyltransferases activity of c35662_g1_i1. Therefore, our results suggested that both c34671_g1_i1 and c35662_g1_i1 are 6'-deoxychalcone 4'-glucosyltransferases but with different substrate preference.

Cloning, Expression, and Functional Characterization of Two Highly Efficient Flavonoid-di-O-glycosyltransferases ZmUGT84A1 and ZmUGT84A2 from Maize (Zea mays L.)

The maize (Zea mays L.) glycosyltransferase family 1 comprises many uridine diphosphate glycosyltransferase (UGT) members. However, UGT activities and biochemical functions have seldom been revealed. In this study, the genes of two flavonoid di-O-glycosyltransferases ZmUGT84A1 and ZmUGT84A2 were cloned from maize plant and expressed in Escherichia coli. Phylogenetic analysis showed that the two enzymes were homologous to AtUGT84A1 and AtUGT84A3. The two recombinant enzymes showed a high conversion rate of luteolin to its glucosides, mainly 4',7-di-O-glucoside and minorly 3',7-di-O-glucoside in two-step glycosylation reactions in vitro. Moreover, the recombinant ZmUGT84A1 and ZmUGT84A2 had a broad substrate spectrum, converting eriodictyol, naringenin, apigenin, quercetin, and kaempferol to monoglucosides and diglucosides. The highly efficient ZmUGT84A1 and ZmUGT84A2 may be used as a tool for the effective synthesis of various flavonoid O-glycosides and as markers for crop breeding to increase O-glycosyl flavonoid content in food.

Genome-Wide Analysis and Identification of UDP Glycosyltransferases Responsive to Chinese Wheat Mosaic Virus Resistance in Nicotiana benthamiana

Glycosylation, a dynamic modification prevalent in viruses and higher eukaryotes, is principally regulated by uridine diphosphate (UDP)-glycosyltransferases (UGTs) in plants. Although UGTs are involved in plant defense responses, their responses to most pathogens, especially plant viruses, remain unclear. Here, we aimed to identify UGTs in the whole genome of Nicotiana benthamiana (N. benthamiana) and to analyze their function in Chinese wheat mosaic virus (CWMV) infection. A total of 147 NbUGTs were identified in N. benthamiana. To conduct a phylogenetic analysis, the UGT protein sequences of N. benthamiana and Arabidopsis thaliana were aligned. The gene structure and conserved motifs of the UGTs were also analyzed. Additionally, the physicochemical properties and predictable subcellular localization were examined in detail. Analysis of cis-acting elements in the putative promoter revealed that NbUGTs were involved in temperature, defense, and hormone responses. The expression levels of 20 NbUGTs containing defense-related cis-acting elements were assessed in CWMV-infected N. benthamiana, revealing a significant upregulation of 8 NbUGTs. Subcellular localization analysis of three NbUGTs (NbUGT12, NbUGT16 and NbUGT17) revealed their predominant localization in the cytoplasm of N. benthamiana leaves, and NbUGT12 was also distributed in the chloroplasts. CWMV infection did not alter the subcellular localization of NbUGT12, NbUGT16, and NbUGT17. Transient overexpression of NbUGT12, NbUGT16, and NbUGT17 enhanced CWMV infection, whereas the knockdown of NbUGT12, NbUGT16 and NbUGT17 inhibited CWMV infection in N. benthamiana. These NbUGTs could serve as potential susceptibility genes to facilitate CWMV infection. Overall, the findings throw light on the evolution and function of NbUGTs.

Methyl jasmonate inducible UGT79A18 is a novel glycosyltransferase involved in the bacoside biosynthetic pathway in Bacopa monnieri

Bacosides are dammarane-type triterpenoidal saponins in Bacopa monnieri and have various pharmacological applications. All the bacosides are diversified from two isomers, i.e., jujubogenin and pseudojujubogenin. The biosynthetic pathway of bacoside is not well elucidated. In the present study, we characterized a UDP-glycosyltransferase, UGT79A18, involved in the glycosylation of pseudojujubogenin. UGT79A18 shows higher expression in response to 5 h of wounding, and 3 h of MeJA treatment. The recombinant UGT79A18 shows in vitro activity against a wide range of flavonoids and triterpenes and has a substrate preference for protopanaxadiol, a dammarane-type triterpene. Secondary metabolite analysis of overexpression and knockdown lines of UGT79A18 in B. monnieri identify bacopasaponin D, bacopaside II, bacopaside N2 and pseudojujubogenin glucosyl rhamnoside as the major bacosides that were differentially accumulated. In the overexpression lines of UGT79A18, we found 1.7-fold enhanced bacopaside II, 8-fold enhanced bacopasaponin D, 3-fold enhanced pseudojujubogenin glucosyl rhamnoside, and 1.6-fold enhanced bacopaside N2 content in comparison with vector control plant, whereas in the knockdown lines of UGT79A18, we found 1.4-fold reduction in bacopaside II content, 3-fold reduction in the bacopasaponin D content, 2-fold reduction in the pseudojujubogenin glucosyl rhamnoside content, and 1.5-fold reduction in bacopaside N2 content in comparison with vector control. These results suggest that UGT79A18 is a significant UDP glycosyltransferase involved in glycosylating pseudojujubogenin and enhancing the pseudojujubogenin-derived bacosides.

Discovering New Substrates of a UDP-Glycosyltransferase with a High-Throughput Method

UDP-glycosyltransferases (UGTs) form a large enzyme family that is found in a wide range of organisms. These enzymes are known for accepting a wide variety of substrates, and they derivatize xenobiotics and metabolites for detoxification. However, most UGT homologs have not been well characterized, and their potential for biomedical and environmental applications is underexplored. In this work, we have used a fluorescent assay for screening substrates of a plant UGT homolog by monitoring the formation of UDP. We optimized the assay such that it could be used for high-throughput screening of substrates of the Medicago truncatula UGT enzyme, UGT71G1, and our results show that 34 of the 159 screened compound samples are potential substrates. With an LC-MS/MS method, we confirmed that three of these candidates indeed were glycosylated by UGT71G1, which includes bisphenol A (BPA) and 7-Ethyl-10-hydroxycamptothecin (SN-38); derivatization of these toxic compounds can lead to new environmental and medical applications. This work suggests that UGT homologs may recognize a substrate profile that is much broader than previously anticipated. Additionally, it demonstrates that this screening method provides a new means to study UDP-glycosyltransferases, facilitating the use of these enzymes to tackle a wide range of problems.

Functional characterization of genes related to triterpene and flavonoid biosynthesis in Cyclocarya paliurus

MAIN CONCLUSION

The oxidosqualene cyclases (OSCs) generating triterpenoid skeletons in Cyclocarya paliurus were identified for the first time, and two uridine diphosphate (UDP)-glycosyltransferases (UGTs) catalyzing the glycosylation of flavonoids were characterized. Cyclocarya paliurus, a native rare dicotyledonous plant in China, contains an abundance of triterpenoid saponins and flavonoid glycosides that exhibit valuable pharmaceutical effects in preventing hypertension, hyperlipidemia, and diabetes. However, the molecular mechanism explaining the biosynthesis of triterpenoid saponin and flavonoid glycoside in C. paliurus remains unclear. In this study, the triterpene content in different tissues and the expression pattern of genes encoding the key enzymes associated with triterpenoid saponin and flavonoid glycoside biosynthesis were studied using transcriptome and metabolome analysis. The eight upstream oxidosqualene cyclases (OSCs) involved in triterpenoid saponin biosynthesis were functionally characterized, among them CpalOSC6 catalyzed 2,3;22,23-dioxidosqualene to form 3-epicabraleadiol; CpalOSC8 cyclized 2,3-oxidosqualene to generate dammarenediol-II; CpalOSC2 and CpalOSC3 produced β-amyrin and CpalOSC4 produced cycloartenol, while CpalOSC2-CpalOSC5, CpalOSC7, and CpalOSC8 all produced lanosterol. However, no catalytic product was detected for CpalOSC1. Moreover, two downstream flavonoid uridine diphosphate (UDP)-glycosyltransferases (UGTs) (CpalUGT015 and CpalUGT100) that catalyze the last step of flavonoid glycoside biosynthesis were functionally elucidated. These results uncovered the key genes involved in the biosynthesis of triterpenoid saponins and flavonoid glycosides in C. paliurus that could be applied to produce flavonoid glycosides and key triterpenoid saponins in the future via a synthetic strategy.

Efficient and Economic Utilization of Cellobiose for Glycosylation Modification by Regulating Carbon Source Supply and Metabolic Pathway In Vivo

Glycosylation, one of the most common and significant modifications in nature, has prompted the development of a cellobiose phosphorolysis route for glycosylation in vivo. However, the process of glycosylation is hampered by the notably low conversion rate of cellobiose. In this work, regulation of the carbon source supply by changing the ratio of glucose to cellobiose improved the conversion rate of cellobiose, resulting in enhancing the efficiency of glycosylation and the production of vitexin. Moreover, three genes (pgm, agp, and ushA) involved in the degradation of UDP-glucose were knocked out to relieve the degradation and diversion of the cellobiose phosphorolysis route. Finally, through the optimization of conversion conditions, we observed a continuous enhancement in cellobiose conversion rate and vitexin production in BL21ΔushAΔagp-TcCGT-CepA, corresponding to an increased concentration of added glucose. The maximum production of vitexin reached 2228 mg/L with the addition of 2 g/L cellobiose and 6 g/L glucose, which was 312% of that in BL21-TcCGT-CepA with the addition of 2 g/L cellobiose. The conversion rate of cellobiose in BL21ΔushAΔagp-TcCGT-CepA reached 88%, which was the highest conversion rate of cellobiose to date. Therefore, this study presents a cost-effective and efficient method to enhance the conversion rate of cellobiose during the glycosylation process.

Flavonols affect the interrelated glucosinolate and camalexin biosynthetic pathways in Arabidopsis thaliana

Flavonols are structurally and functionally diverse biomolecules involved in plant biotic and abiotic stress tolerance, pollen development, and inhibition of auxin transport. However, their effects on global gene expression and signaling pathways are unclear. To explore the roles of flavonol metabolites in signaling, we performed comparative transcriptome and targeted metabolite profiling of seedlings from the flavonol-deficient Arabidopsis loss-of-function mutant flavonol synthase1 (fls1) with and without exogenous supplementation of flavonol derivatives (kaempferol, quercetin, and rutin). RNA-seq results indicated that flavonols modulate various biological and metabolic pathways, with significant alterations in camalexin and aliphatic glucosinolate synthesis. Flavonols negatively regulated camalexin biosynthesis but appeared to promote the accumulation of aliphatic glucosinolates via transcription factor-mediated up-regulation of biosynthesis genes. Interestingly, upstream amino acid biosynthesis genes involved in methionine and tryptophan synthesis were altered under flavonol deficiency and exogenous supplementation. Quercetin treatment significantly up-regulated aliphatic glucosinolate biosynthesis genes compared with kaempferol and rutin. In addition, expression and metabolite analysis of the transparent testa7 mutant, which lacks hydroxylated flavonol derivatives, clarified the role of quercetin in the glucosinolate biosynthesis pathway. This study elucidates the molecular mechanisms by which flavonols interfere with signaling pathways, their molecular targets, and the multiple biological activities of flavonols in plants.

Disruption of a licorice cellulose synthase-derived glycosyltransferase gene demonstrates its in planta role in soyasaponin biosynthesis

KEY MESSAGE

CRISPR-Cas9-mediated disruption of a licorice cellulose synthase-derived glycosyltransferase gene, GuCSyGT, demonstrated the in planta role of GuCSyGT as the enzyme catalyzing 3-O-glucuronosylation of triterpenoid aglycones in soyasaponin biosynthesis. Triterpenoid glycosides (saponins) are a large, structurally diverse group of specialized metabolites in plants, including the sweet saponin glycyrrhizin produced by licorice (Glycyrrhiza uralensis) and soyasaponins that occur widely in legumes, with various bioactivities. The triterpenoid saponin biosynthetic pathway involves the glycosylation of triterpenoid sapogenins (the non-sugar part of triterpenoid saponins) by glycosyltransferases (GTs), leading to diverse saponin structures. Previously, we identified a cellulose synthase-derived GT (CSyGT), as a newly discovered class of triterpenoid GT from G. uralensis. GuCSyGT expressed in yeast, which could transfer the sugar glucuronic acid to the C3 position of glycyrrhetinic acid and soyasapogenol B, which are the sapogenins of glycyrrhizin and soyasaponin I, respectively. This suggested that GuCSyGT is involved in the biosynthesis of glycyrrhizin and soyasaponin I. However, the in planta role of GuCSyGT in saponin biosynthesis remains unclear. In this study, we generated GuCSyGT-disrupted licorice hairy roots using CRISPR-Cas9-mediated genome editing and analyzed the saponin content. This revealed that soyasaponin I was completely absent in GuCSyGT-disrupted lines, demonstrating the in planta role of GuCSyGT in saponin biosynthesis.

Genome-wide analysis of UDP-glycosyltransferase gene family and identification of a flavonoid 7-O-UGT (AhUGT75A) enhancing abiotic stress in peanut (Arachis hypogaea L.)

BACKGROUND

Glycosylation, catalyzed by UDP-glycosyltransferase (UGT), was important for enhancing solubility, bioactivity, and diversity of flavonoids. Peanut (Arachis hypogaea L.) is an important oilseed and cash crop worldwide. In addition to provide high quality of edible oils and proteins, peanut seeds contain a rich source of flavonoid glycosides that benefit human health. However, information of UGT gene family was quite limited in peanut.

RESULTS

In present study, a total of 267 AhUGTs clustered into 15 phylogenetic groups were identified in peanut genome. Group I has greatly expanded to contain the largest number of AhUGT genes. Segmental duplication was the major driving force for AhUGT gene family expansion. Transcriptomic analysis of gene expression profiles in various tissues and under different abiotic stress treatments indicated AhUGTs were involved in peanut growth and abiotic stress response. AhUGT75A (UGT73CG33), located in mitochondria, was characterized as a flavonoid 7-O-UGT by in vitro enzyme assays. The transcript level of AhUGT75A was strongly induced by abiotic stress. Overexpression of AhUGT75A resulted in accumulating less amount of malondialdehyde (MDA) and superoxide, and enhancing tolerance against drought and/or salt stress in transgenic Arabidopsis. These results indicated AhUGT75A played important roles in conferring abiotic stress tolerance through reactive oxygen species scavenging.

CONCLUSIONS

Our research only not provides valuable information for functional characterization of UGTs in peanut, but also gives new insights into potential applications in breeding new cultivars with both desirable stress tolerance and health benefits.

Anabolic metabolism of autotoxic substance coumarins in plants

Background

Autotoxicity is an intraspecific manifestation of allelopathy in plant species. The specialized metabolites and their derivatives that cause intraspecific allelopathic inhibition in the plant are known as autotoxic substances. Consequently, autotoxic substances production seriously affects the renewal and stability of ecological communities.

Methods

This article systematically summarizes the types of autotoxic substances present in different plants. They mainly include phenolic compounds, terpenoids, and nitrogenous organic compounds. Phenolic coumarins are the main autotoxic substances in many plants. Therefore, we also discuss differences in coumarin types and content among plant varieties, developmental stages, and tissue parts, as well as their mechanisms of autotoxicity. In addition, we review the metabolic pathways involved in coumarin biosynthesis, the key enzymes, genes, and transcription factors, as well as factors affecting coumarin biosynthesis.

Results

Coumarin biosynthesis involves three stages: (1) the formation of the coumarin nucleus; (2) acylation, hydroxylation, and cyclization; (3) structural modification. The key enzymes involved in the coumarin nuclear formation stage include PAL, C4H, 4CL, HCT, CAOMT, COSY, F6'H, and CCoAOMT1, and the key genes involved include BGA, CYP450 and MDR, among others. Ortho-hydroxylation is a key step in coumarin biosynthesis and PS, COSY and S8H are the key enzymes involved in this process. Finally, UGTs are responsible for the glycosylation modification of coumarins, and the MaUGT gene may therefore be involved in coumarin biosynthesis.

Conclusion

It is important to elucidate the autotoxicity and anabolic mechanisms of coumarins to create new germplasms that produce fewer autotoxic substances.

Biochemical Characterization of Parsley Glycosyltransferases Involved in the Biosynthesis of a Flavonoid Glycoside, Apiin

The flavonoid glycoside apiin (apigenin 7-O-[β-D-apiosyl-(1→2)-β-D-glucoside]) is abundant in apiaceous and asteraceous plants, including celery and parsley. Although several enzymes involved in apiin biosynthesis have been identified in celery, many of the enzymes in parsley (Petroselinum crispum) have not been identified. In this study, we identified parsley genes encoding the glucosyltransferase, PcGlcT, and the apiosyltransferase, PcApiT, that catalyze the glycosylation steps of apiin biosynthesis. Their substrate specificities showed that they were involved in the biosynthesis of some flavonoid 7-O-apiosylglucosides, including apiin. The expression profiles of PcGlcT and PcApiT were closely correlated with the accumulation of flavonoid 7-O-apiosylglucosides in parsley organs and developmental stages. These findings support the idea that PcGlcT and PcApiT are involved in the biosynthesis of flavonoid 7-O-apiosylglucosides in parsley. The identification of these genes will elucidate the physiological significance of apiin and the development of apiin production methods.

Structural and functional studies reveal the molecular basis of substrate promiscuity of a glycosyltransferase originating from a major agricultural pest

The two-spotted spider mite, Tetranychus urticae, is a major cosmopolitan pest that feeds on more than 1100 plant species. Its genome contains an unprecedentedly large number of genes involved in detoxifying and transporting xenobiotics, including 80 genes that code for UDP glycosyltransferases (UGTs). These enzymes were acquired via horizontal gene transfer from bacteria after loss in the Chelicerata lineage. UGTs are well-known for their role in phase II metabolism; however, their contribution to host adaptation and acaricide resistance in arthropods, such as T. urticae, is not yet resolved. TuUGT202A2 (Tetur22g00270) has been linked to the ability of this pest to adapt to tomato plants. Moreover, it was shown that this enzyme can glycosylate a wide range of flavonoids. To understand this relationship at the molecular level, structural, functional, and computational studies were performed. Structural studies provided specific snapshots of the enzyme in different catalytically relevant stages. The crystal structure of TuUGT202A2 in complex with UDP-glucose was obtained and site-directed mutagenesis paired with molecular dynamic simulations revealed a novel lid-like mechanism involved in the binding of the activated sugar donor. Two additional TuUGT202A2 crystal complexes, UDP-(S)-naringenin and UDP-naringin, demonstrated that this enzyme has a highly plastic and open-ended acceptor-binding site. Overall, this work reveals the molecular basis of substrate promiscuity of TuUGT202A2 and provides novel insights into the structural mechanism of UGTs catalysis.

A Muti-Substrate Flavonol O-glucosyltransferases from Safflower

To explore the complete biosynthesis process of flavonoid glycosides in safflower, specifically the key glycosyltransferase that might be involved, as well as to develop an efficient biocatalyst to synthesize flavonoid glycosides, a glycosyltransferase CtUGT4, with flavonoid-O-glycosyltransferase activity, was identified in safflower. The fusion protein of CtUGT4 was heterologously expressed in Escherichia coli, and the target protein was purified. The recombinant protein can catalyze quercetin to form quercetin-7-O-glucoside, and kaempferol to form kaempferol-3-O in vitro, and a series of flavones, flavonols, dihydroflavones, chalcones, and chalcone glycosides were used as substrates to generate new products. CtUGT4 was expressed in the tobacco transient expression system, and the enzyme activity results showed that it could catalyze kaempferol to kaempferol-3-O-glucoside, and quercetin to quercetin-3-O-glucoside. After overexpressing CtUGT4 in safflower, the content of quercetin-3-O-rutinoside in the safflower florets increased significantly, and the content of quercetin-3-O-glucoside also tended to increase, which preliminarily confirmed the function of CtUGT4 flavonoid-O-glycosyltransferase. This work demonstrated the flavonoid-O-glycosyltransferase function of safflower CtUGT4 and showed differences in the affinity for different flavonoid substrates and the regioselectivity of catalytic sites in safflower, both in vivo and in vitro, providing clues for further research regarding the function of UGT genes, as well as new ideas for the cultivation engineering of the directional improvement of effective metabolites in safflower.

Unraveling the serial glycosylation in the biosynthesis of steroidal saponins in the medicinal plant Paris polyphylla and their antifungal action

Sugar-sugar glycosyltransferases play important roles in constructing complex and bioactive saponins. Here, we characterized a series of UDP-glycosyltransferases responsible for biosynthesizing the branched sugar chain of bioactive steroidal saponins from a widely known medicinal plant Paris polyphylla var. yunnanensis. Among them, a 2'-O-rhamnosyltransferase and three 6'-O-glucosyltrasferases catalyzed a cascade of glycosylation to produce steroidal diglycosides and triglycosides, respectively. These UDP-glycosyltransferases showed astonishing substrate promiscuity, resulting in the generation of a panel of 24 terpenoid glycosides including 15 previously undescribed compounds. A mutant library containing 44 variants was constructed based on the identification of critical residues by molecular docking simulations and protein model alignments, and a mutant UGT91AH1Y187A with increased catalytic efficiency was obtained. The steroidal saponins exhibited remarkable antifungal activity against four widespread strains of human pathogenic fungi attributed to ergosterol-dependent damage of fungal cell membranes, and 2'-O-rhamnosylation appeared to correlate with strong antifungal effects. The findings elucidated the biosynthetic machinery for their production of steroidal saponins and revealed their potential as new antifungal agents.

Structure-function and engineering of plant UDP-glycosyltransferase

Natural products synthesized by plants have substantial industrial and medicinal values and are therefore attracting increasing interest in various related industries. Among the key enzyme families involved in the biosynthesis of natural products, uridine diphosphate-dependent glycosyltransferases (UGTs) play a crucial role in plants. In recent years, significant efforts have been made to elucidate the catalytic mechanisms and substrate recognition of plant UGTs and to improve them for desired functions. In this review, we presented a comprehensive overview of all currently published structures of plant UGTs, along with in-depth analyses of the corresponding catalytic and substrate recognition mechanisms. In addition, we summarized and evaluated the protein engineering strategies applied to improve the catalytic activities of plant UGTs, with a particular focus on high-throughput screening methods. The primary objective of this review is to provide readers with a comprehensive understanding of plant UGTs and to serve as a valuable reference for the latest techniques used to improve their activities.

Tetraose steroidal glycoalkaloids from potato provide resistance against Alternaria solani and Colorado potato beetle

Plants with innate disease and pest resistance can contribute to more sustainable agriculture. Natural defence compounds produced by plants have the potential to provide a general protective effect against pathogens and pests, but they are not a primary target in resistance breeding. Here, we identified a wild relative of potato, Solanum commersonii, that provides us with unique insight in the role of glycoalkaloids in plant immunity. We cloned two atypical resistance genes that provide resistance to Alternaria solani and Colorado potato beetle through the production of tetraose steroidal glycoalkaloids (SGA). Moreover, we provide in vitro evidence to show that these compounds have potential against a range of different (potato pathogenic) fungi. This research links structural variation in SGAs to resistance against potato diseases and pests. Further research on the biosynthesis of plant defence compounds in different tissues, their toxicity, and the mechanisms for detoxification, can aid the effective use of such compounds to improve sustainability of our food production.

ATP binding cassette transporters and uridine diphosphate glycosyltransferases are ancient protein families that evolved roles in herbicide resistance through exaptation

ATP-binding cassette (ABC) transporters actively transport various substances across membranes, while uridine diphosphate (UDP) glycosyltransferases (UGTs) are proteins that catalyse the chemical modification of various organic compounds. Both of these protein superfamilies have been associated with conferring herbicide resistance in weeds. Little is known about the evolutionary history of these protein families in the Archaeplastida. To infer the evolutionary histories of these protein superfamilies, we compared protein sequences collected from 10 species which represent distinct lineages of the Archaeplastida-the lineage including glaucophyte algae, rhodophyte algae, chlorophyte algae and the streptophytes-and generated phylogenetic trees. We show that ABC transporters were present in the last common ancestor of the Archaeplastida which lived 1.6 billion years ago, and the major clades identified in extant plants were already present then. Conversely, we only identified UGTs in members of the streptophyte lineage, which suggests a loss of these proteins in earlier diverging Archaeplastida lineages or arrival of UGTs into a common ancestor of the streptophyte lineage through horizontal gene transfer from a non-Archaeplastida eukaryote lineage. We found that within the streptophyte lineage, most diversification of the UGT protein family occurred in the vascular lineage, with 17 of the 20 clades identified in extant plants present only in vascular plants. Based on our findings, we conclude that ABC transporters and UGTs are ancient protein families which diversified during Archaeplastida evolution, which may have evolved for developmental functions as plants began to occupy new environmental niches and are now being selected to confer resistance to a diverse range of herbicides in weeds.

The chemical profiling of Salvia plebeia during different growth periods and the biosynthesis of its main flavonoids ingredients

Salvia plebeia (Lamiaceae) is a valuable medicinal plant widely distributed across Asia and Oceania. However, the composition and accumulation patterns of its active ingredients in different organs during the growth and their biosynthetic mechanism remain unknown. Therefore, we conducted metabolite profiling, transcriptomic analysis, and biological functional verification to explore the distribution, accumulation, and biosynthesis mechanisms of flavonoids in S. plebeia. We identified 70 metabolites including 46 flavonoids, 16 phenolic acids, seven terpenoids, and one organic acid, of which 21 were previously unreported in S. plebeia. Combining metabolomic-transcriptomic analysis and biological functional verification, we identified the key genes involved in biosynthesis of its main active ingredients, hispidulin and homoplantaginin, including SpPAL, SpC4H, Sp4CL2, Sp4CL5, SpCHS1, SpCHI, SpFNS, SpF6H1, SpF6OMT1, SpF6OMT2, SpUGT1, SpUGT2, and SpUGT3. Using the identified genes, we reconstructed the hispidulin and homoplantaginin biosynthesis pathways in Escherichia coli, and obtained a yield of 5.33 and 3.86 mg/L for hispidulin and homoplantaginin, respectively. Our findings provide valuable insights into the changes in chemical components in different organs of S. plebeia during different growth and harvest stages and establishes a foundation for identifying and synthesizing its active components.

Protein Modelling Highlighted Key Catalytic Sites Involved in Position-Specific Glycosylation of Isoflavonoids

Uridine diphosphate glycosyltransferases (UGTs) are known for promiscuity towards sugar acceptors, a valuable characteristic for host plants but not desirable for heterologous biosynthesis. UGTs characterized for the O-glycosylation of isoflavonoids have shown a variable efficiency, substrate preference, and OH site specificity. Thus, 22 UGTs with reported isoflavonoid O-glycosylation activity were analyzed and ranked for OH site specificity and catalysis efficiency. Multiple-sequence alignment (MSA) showed a 33.2% pairwise identity and 4.5% identical sites among selected UGTs. MSA and phylogenetic analysis highlighted a comparatively higher amino acid substitution rate in the N-terminal domain that likely led to a higher specificity for isoflavonoids. Based on the docking score, OH site specificity, and physical and chemical features of active sites, selected UGTs were divided into three groups. A significantly high pairwise identity (67.4%) and identical sites (31.7%) were seen for group 1 UGTs. The structural and chemical composition of active sites highlighted key amino acids that likely define substrate preference, OH site specificity, and glycosylation efficiency towards selected (iso)flavonoids. In conclusion, physical and chemical parameters of active sites likely control the position-specific glycosylation of isoflavonoids. The present study will help the heterologous biosynthesis of glycosylated isoflavonoids and protein engineering efforts to improve the substrate and site specificity of UGTs.

Integrated transcriptomic and metabolomic analysis revealed altitude-related regulatory mechanisms on flavonoid accumulation in potato tubers

Not least because it is adaptable to a variety of geographies and climates, potato (Solanum tuberosum L.) is grown across much of the world. Pigmented potato tubers have been found to contain large quantities of flavonoids, which have various functional roles and act as antioxidants in the human diet. However, the effect of altitude on the biosynthesis and accumulation of flavonoids in potato tubers is poorly characterized. Here we carried out an integrated metabolomic and transcriptomic study in order to evaluate how cultivation at low (800 m), moderate (1800 m), and high (3600 m) altitude affects flavonoid biosynthesis in pigmented potato tubers. Both red and purple potato tubers grown at a high altitude contained the highest flavonoid content, and the most highly pigmented flesh, followed by those grown at a low altitude. Co-expression network analysis revealed three modules containing genes which were positively correlated with altitude-responsive flavonoid accumulation. The anthocyanin repressors StMYBATV and StMYB3 exhibited a significant positive relationship with altitude-responsive flavonoid accumulation. The repressive function of StMYB3 was further verified in tobacco flowers and potato tubers. The results presented here add to the growing body of knowledge regarding the response of flavonoid biosynthesis to environmental conditions, and should aid in efforts to develop novel varieties of pigmented potatoes for use across different geographies.

Proteomics Identified UDP-Glycosyltransferase Family Members as Pro-Viral Factors for Turnip Mosaic Virus Infection in Nicotiana benthamiana

Viruses encounter numerous host factors that facilitate or suppress viral infection. Although some host factors manipulated by viruses were uncovered, we have limited knowledge of the pathways hijacked to promote viral replication and activate host defense responses. Turnip mosaic virus (TuMV) is one of the most prevalent viral pathogens in many regions of the world. Here, we employed an isobaric tag for relative and absolute quantitation (iTRAQ)-based proteomics approach to characterize cellular protein changes in the early stages of infection of Nicotiana benthamiana by wild type and replication-defective TuMV. A total of 225 differentially accumulated proteins (DAPs) were identified (182 increased and 43 decreased). Bioinformatics analysis showed that a few biological pathways were associated with TuMV infection. Four upregulated DAPs belonging to uridine diphosphate-glycosyltransferase (UGT) family members were validated by their mRNA expression profiles and their effects on TuMV infection. NbUGT91C1 or NbUGT74F1 knockdown impaired TuMV replication and increased reactive oxygen species production, whereas overexpression of either promoted TuMV replication. Overall, this comparative proteomics analysis delineates the cellular protein changes during early TuMV infection and provides new insights into the role of UGTs in the context of plant viral infection.

Genome-wide identification of UDP-glycosyltransferases in the tea plant (Camellia sinensis) and their biochemical and physiological functions

Tea (Camellia sinensis) has been an immensely important commercially grown crop for decades. This is due to the presence of essential nutrients and plant secondary metabolites that exhibit beneficial health effects. UDP-glycosyltransferases (UGTs) play an important role in the diversity of such secondary metabolites by catalysing the transfer of an activated sugar donor to acceptor molecules, and thereby creating a huge variety of glycoconjugates. Only in recent years, thanks to the sequencing of the tea plant genome, have there been increased efforts to characterise the UGTs in C. sinensis to gain an understanding of their physiological role and biotechnological potential. Based on the conserved plant secondary product glycosyltransferase (PSPG) motif and the catalytically active histidine in the active site, UGTs of family 1 in C. sinensis are identified here, and shown to cluster into 21 groups in a phylogenetic tree. Building on this, our current understanding of recently characterised C. sinensis UGTs (CsUGTs) is highlighted and a discussion on future perspectives made.

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

MAIN CONCLUSION

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