Functional Characterization of UDP-Glycosyltransferases Involved in Anti-viral Lignan Glycosides Biosynthesis in Isatis indigotica

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.

Plant-Derived UDP-Glycosyltransferases for Glycosylation-Mediated Detoxification of Deoxynivalenol: Enzyme Discovery, Characterization, and In Vivo Resistance Assessment

Fungal infections of crops pose a threat to global agriculture. Fungi of the genus Fusarium cause widespread diseases in cereal crops. Fusarium graminearum reduces yields and produces harmful mycotoxins such as deoxynivalenol (DON). Plants mitigate DON toxicity through glucose conjugation mediated by UDP-glycosyltransferases (UGTs), forming deoxynivalenol-3-O-glucoside (DON-3-Glc). Few such UGTs have been identified, predominantly from Fusarium-susceptible crops. Given that the presence of this activity in diverse plants and across broader UGT subfamilies and groups was underexplored, we screened a library of 380 recombinant plant UGTs and identified and characterized eight novel enzymes glycosylating DON in vitro. Among these, ZjUGT from Ziziphus jujuba stood out with the highest activity, showing an apparent kcat of 0.93 s-1 and kcat/Km of 2450 M-1 s-1. Interestingly, four enzymes produced primarily a novel, still uncharacterized glucoside. Furthermore, we evaluated the in vivo resistance provided by these UGTs when expressed in a DON-sensitive yeast strain. At least six of the novel UGTs conferred some level of resistance, allowing growth at concentrations of up to 120 mg/L of DON. This study contributes to potential strategies to enhance DON resistance in cereal crops in the future.

The ERF transcription factor LTF1 activates DIR1 to control stereoselective synthesis of antiviral lignans and stress defense in Isatis indigotica roots

Lignans are a powerful weapon for plants to resist stresses and have diverse bioactive functions to protect human health. Elucidating the mechanisms of stereoselective biosynthesis and response to stresses of lignans is important for the guidance of plant improvement. Here, we identified the complete pathway to stereoselectively synthesize antiviral (-)-lariciresinol glucosides in Isatis indigotica roots, which consists of three-step sequential stereoselective enzymes DIR1/2, PLR, and UGT71B2. DIR1 was further identified as the key gene in respoJanuary 2024nse to stresses and was able to trigger stress defenses by mediating the elevation in lignan content. Mechanistically, the phytohormone-responsive ERF transcription factor LTF1 colocalized with DIR1 in the cell periphery of the vascular regions in mature roots and helped resist biotic and abiotic stresses by directly regulating the expression of DIR1. These systematic results suggest that DIR1 as the first common step of the lignan pathway cooperates with PLR and UGT71B2 to stereoselectively synthesize (-)-lariciresinol derived antiviral lignans in I. indigotica roots and is also a part of the LTF1-mediated regulatory network to resist stresses. In conclusion, the LTF1-DIR1 module is an ideal engineering target to improve plant Defenses while increasing the content of valuable lignans in plants.

Combined metabolomic and transcriptomic analysis reveals the characteristics of the lignan in Isatis indigotica Fortune

Isatis indigotica Fortune is a plant species containing lignan compounds of significant economic value. Its root plays a crucial role in treating viruses and exhibits antitumor, anti-inflammatory, antibacterial, and other biological activities. Now, I. indigotica has been included in Isatis tinctoria Linnaeus. In this study, the roots of diploid I. indigotica, tetraploid I. indigotica, and Isatis tinctoria Linnaeus were analyzed using metabolome and transcriptome analysis. The metabolomic analysis detected 48 lignan metabolites, including Lirioresinol A, Vladinol A, Syringaresinol, Arctigenin, Acanthoside B, and Sesamin as characteristic compounds, without significant variations among the remaining metabolites. The transcriptomic analysis identified 41 differentially expressed phenylpropanoid synthase genes, which were further analyzed for variations in lignan transcriptome profiles across different samples. RT-qPCR analysis also revealed differential genes expression related to lignan biosynthesis pathway among the three sample groups. The analysis of transcription factors showed that the AP2-EREBP family (Iin24319), MYB family (Iin24843), and WRKY family (Iin08158) displayed expression patterns similar to Iin14549. Phylogenetic analyses also indicate that Iin14549 may play a role in lignan synthesis. These transcription factor families exhibited high expression in tetraploid I. indigotica, moderate expression in diploid I. indigotica, and low expression in I. tinctoria. The findings of this study can serve as a reference for improving the quality of I. indigotica and developing germplasms with high lignan content. Additionally, these results lay a foundation for the functional characterization of UGTs in lignan biosynthesis pathway.

Pour some sugar on me: The diverse functions of phenylpropanoid glycosylation

The phenylpropanoid metabolism is the source of a vast array of specialized metabolites that play diverse functions in plant growth and development and contribute to all aspects of plant interactions with their surrounding environment. These compounds protect plants from damaging ultraviolet radiation and reactive oxygen species, provide mechanical support for the plants to stand upright, and mediate plant-plant and plant-microorganism communications. The enormous metabolic diversity of phenylpropanoids is further expanded by chemical modifications known as "decorative reactions", including hydroxylation, methylation, glycosylation, and acylation. Among these modifications, glycosylation is the major driving force of phenylpropanoid structural diversification, also contributing to the expansion of their properties. Phenylpropanoid glycosylation is catalyzed by regioselective uridine diphosphate (UDP)-dependent glycosyltransferases (UGTs), whereas glycosyl hydrolases known as β-glucosidases are the major players in deglycosylation. In this article, we review how the glycosylation process affects key physicochemical properties of phenylpropanoids, such as molecular stability and solubility, as well as metabolite compartmentalization/storage and biological activity/toxicity. We also summarize the recent knowledge on the functional implications of glycosylation of different classes of phenylpropanoid compounds. A balance of glycosylation/deglycosylation might represent an essential molecular mechanism to regulate phenylpropanoid homeostasis, allowing plants to dynamically respond to diverse environmental signals.

Validation of a metabolite-GWAS network for Populus trichocarpa family 1 UDP-glycosyltransferases

Metabolite genome-wide association studies (mGWASs) are increasingly used to discover the genetic basis of target phenotypes in plants such as Populus trichocarpa, a biofuel feedstock and model woody plant species. Despite their growing importance in plant genetics and metabolomics, few mGWASs are experimentally validated. Here, we present a functional genomics workflow for validating mGWAS-predicted enzyme-substrate relationships. We focus on uridine diphosphate-glycosyltransferases (UGTs), a large family of enzymes that catalyze sugar transfer to a variety of plant secondary metabolites involved in defense, signaling, and lignification. Glycosylation influences physiological roles, localization within cells and tissues, and metabolic fates of these metabolites. UGTs have substantially expanded in P. trichocarpa, presenting a challenge for large-scale characterization. Using a high-throughput assay, we produced substrate acceptance profiles for 40 previously uncharacterized candidate enzymes. Assays confirmed 10 of 13 leaf mGWAS associations, and a focused metabolite screen demonstrated varying levels of substrate specificity among UGTs. A substrate binding model case study of UGT-23 rationalized observed enzyme activities and mGWAS associations, including glycosylation of trichocarpinene to produce trichocarpin, a major higher-order salicylate in P. trichocarpa. We identified UGTs putatively involved in lignan, flavonoid, salicylate, and phytohormone metabolism, with potential implications for cell wall biosynthesis, nitrogen uptake, and biotic and abiotic stress response that determine sustainable biomass crop production. Our results provide new support for in silico analyses and evidence-based guidance for in vivo functional characterization.

Molecular identification and functional characterization of two glycosyltransferases genes from Fallopia multiflora

The traditional Chinese medicine plant Fallopia multiflora (Thunb.) Harald. contains various pharmacodynamically active glycosides, such as stilbene glycosides, anthraquinone (AQ) glycosides, and flavonoid glycosides. Glycosylation is an important reaction in plant metabolism that is generally completed by glycosyltransferase in the last step of the secondary metabolite biosynthesis pathway, and it can improve the beneficial properties of many natural products. In this study, based on the transcriptome data of F. multiflora, we cloned two Uridine-diphosphate-dependent glycosyltransferases (UGTs) from the cDNA of F. multiflora (FmUGT1 and FmUGT2). Their full-length sequences were 1602 and 1449 bp, encoding 533 and 482 amino acids, respectively. In vitro enzymatic reaction results showed that FmUGT1 and FmUGT2 were promiscuous and could catalyze the glycosylation of 12 compounds, including stilbenes, anthraquinones, flavonoids, phloretin, and curcumin, and we also obtained and structurally identified 13 glycosylated products from both of them. Further experiments on the in vivo function of FmUGT1 and FmUGT2 showed that 2, 3, 5, 4'- tetrahydroxy stilbene-2-O-β-d-glucoside (THSG) content in hairy roots was elevated significantly when FmUGT1 and FmUGT2 were overexpressed and decreased accordingly in the RNA interference (RNAi) groups. These results indicate that FmUGT1 and FmUGT2 were able to glycosylate a total of 12 structurally diverse types of acceptors and to generate O-glycosides. In addition, FmUGT1 and FmUGT2 efficiently catalyzed the biosynthesis of THSG, and promoted the production of AQs in transgenic hairy roots.