Substrate specificity and safener inducibility of the plant UDP-glucose-dependent family 1 glycosyltransferase super-family

UDP-glycosyltransferase UGT96C10 functions as a novel detoxification factor for conjugating the activated dinitrotoluene sulfonate in switchgrass

Dinitrotoluene sulfonates (DNTSes) are highly toxic hazards regulated by the Resource Conservation and Recovery Act (RCRA) in the United States. The trinitrotoluene (TNT) red water formed during the TNT purification process consists mainly of DNTSes. Certain plants, including switchgrass, reed and alfalfa, can detoxify low concentrations of DNTS in TNT red water-contaminated soils. However, the precise mechanism by which these plants detoxify DNTS remains unknown. In order to aid in the development of phytoremediation resources with high DNTS removal rates, we identified and characterized 1-hydroxymethyl-2,4-dinitrobenzene sulfonic acid (HMDNBS) and its glycosylated product HMDNBS O-glucoside as the degradation products of 2,4-DNT-3-SO3Na, the major isoform of DNTS in TNT red water-contaminated soils, in switchgrass via LC-MS/MS- and NMR-based metabolite analyses. Transcriptomic analysis revealed that 15 UDP-glycosyltransferase genes were dramatically upregulated in switchgrass plants following 2,4-DNT-3-SO3Na treatment. We expressed, purified and assayed the activity of recombinant UGT proteins in vitro and identified PvUGT96C10 as the enzyme responsible for the glycosylation of HMDNBS in switchgrass. Overexpression of PvUGT96C10 in switchgrass significantly alleviated 2,4-DNT-3-SO3Na-induced plant growth inhibition. Notably, PvUGT96C10-overexpressing transgenic switchgrass plants removed 83.1% of 2,4-DNT-3-SO3Na in liquid medium after 28 days, representing a 3.2-fold higher removal rate than that of control plants. This work clarifies the DNTS detoxification mechanism in plants for the first time, suggesting that PvUGT96C10 is crucial for DNTS degradation. Our results indicate that PvUGT96C10-overexpressing plants may hold great potential for the phytoremediation of TNT red water-contaminated soils.

UDP-glucosyltransferase 71C4 controls the flux of phenylpropanoid metabolism to shape cotton seed development

Seeds play a crucial role in plant reproduction, making it essential to identify genes that affect seed development. In this study, we focused on UDP-glucosyltransferase 71C4 (UGT71C4) in cotton, a member of the glycosyltransferase family that shapes seed width and length, thereby influencing seed index and seed cotton yield. Overexpression of UGT71C4 results in seed enlargement owing to its glycosyltransferase activity on flavonoids, which redirects metabolic flux from lignin to flavonoid metabolism. This shift promotes cell proliferation in the ovule via accumulation of flavonoid glycosides, significantly enhancing seed cotton yield and increasing the seed index from 10.66 g to 11.91 g. By contrast, knockout of UGT71C4 leads to smaller seeds through activation of the lignin metabolism pathway and redirection of metabolic flux back to lignin synthesis. This redirection leads to increased ectopic lignin deposition in the ovule, inhibiting ovule growth and development, and alters yield components, increasing the lint percentage from 41.42% to 43.40% and reducing the seed index from 10.66 g to 8.60 g. Our research sheds new light on seed size development and reveals potential pathways for enhancing seed yield.

Discovery, characterization, and comparative analysis of new UGT72 and UGT84 family glycosyltransferases

Glycosylated derivatives of natural product polyphenols display a spectrum of biological activities, rendering them critical for both nutritional and pharmacological applications. Their enzymatic synthesis by glycosyltransferases is frequently constrained by the limited repertoire of characterized enzyme-catalyzed transformations. Here, we explore the glycosylation capabilities and substrate preferences of newly identified plant uridine diphosphate (UDP)-dependent glycosyltransferases (UGTs) within the UGT72 and UGT84 families, with particular focus on natural polyphenol glycosylation from UDP-glucose. Four UGTs are classified according to their phylogenetic relationships and reaction products, identifying them as biocatalysts for either glucoside (UGT72 enzymes) or glucose ester (UGT84 members) formation from selected phenylpropanoid compounds. Detailed kinetic evaluations expose the unique attributes of these enzymes, including their specific activities and regio-selectivities towards diverse polyphenolic substrates, with product characterizations validating the capacity of UGT84 family members to perform di-O-glycosylation on flavones. Sequence analysis coupled with structural predictions through AlphaFold reveal an unexpected absence of a conserved threonine residue across all four enzymes, a trait previously linked to pentosyltransferases. This comparative analysis broadens the understood substrate specificity range for UGT72 and UGT84 enzymes, enhancing our understanding of their utility in the production of natural phenolic glycosides. The findings from this in-depth characterization provide valuable insights into the functional versatility of UGT-mediated reactions.

Genome-wide analysis of UDP-glycosyltransferases family and identification of UGT genes involved in drought stress of Platycodon grandiflorus

Introduction

The uridine diphosphate (UDP)-glycosyltransferase (UGT) family is the largest glycosyltransferase family, which is involved in the biosynthesis of natural plant products and response to abiotic stress. UGT has been studied in many medicinal plants, but there are few reports on Platycodon grandiflorus. This study is devoted to genome-wide analysis of UGT family and identification of UGT genes involved in drought stress of Platycodon grandiflorus (PgUGTs).

Methods

The genome data of Platycodon grandiflorus was used for genome-wide identification of PgUGTs, online website and bioinformatics analysis software was used to conduct bioinformatics analysis of PgUGT genes and the genes highly responsive to drought stress were screened out by qRT-PCR, these genes were cloned and conducted bioinformatics analysis.

Results

A total of 75 PgUGT genes were identified in P.grandiflorus genome and clustered into 14 subgroups. The PgUGTs were distributed on nine chromosomes, containing multiple cis-acting elements and 22 pairs of duplicate genes were identified. Protein-protein interaction analysis was performed to predict the interaction between PgUGT proteins. Additionally, six genes were upregulated after 3d under drought stress and three genes (PGrchr09G0563, PGrchr06G0523, PGrchr06G1266) responded significantly to drought stress, as confirmed by qRT-PCR. This was especially true for PGrchr06G1266, the expression of which increased 16.21-fold after 3d of treatment. We cloned and conducted bioinformatics analysis of three candidate genes, both of which contained conserved motifs and several cis-acting elements related to stress response, PGrchr06G1266 contained the most elements.

Discussion

PgGT1 was confirmed to catalyze the C-3 position of platycodin D and only eight amino acids showed differences between gene PGr008G1527 and PgGT1, which means PGr008G1527 may be able to catalyze the C-3 position of platycodin D in the same manner as PgGT1. Seven genes were highly expressed in the roots, stems, and leaves, these genes may play important roles in the development of the roots, stems, and leaves of P. grandiflorus. Three genes were highly responsive to drought stress, among which the expression of PGrchr06G1266 was increased 16.21-fold after 3d of drought stress treatment, indicating that PGrchr06G1266 plays an important role in drought stress tolerance. To summarize, this study laied the foundation to better understand the molecular bases of responses to drought stress and the biosynthesis of platycodin.

Pyroxasulfone Metabolism in Resistant Lolium rigidum: Is It All Down to GST Activity?

Resistance to the herbicide pyroxasulfone has slowly but steadily increased in agricultural weeds. The evolved resistance of one Lolium rigidum population has been attributed to the conjugation of pyroxasulfone to reduced glutathione, mediated by glutathione transferase (GST) activity. To determine if GST-based metabolism is a widespread mechanism of pyroxasulfone resistance in L. rigidum, a number of putative-resistant populations were screened for GST activity toward pyroxasulfone, the presence of GSTF13-like isoforms (previously implicated in pyroxasulfone conjugation in this species), tissue glutathione concentrations, and response to inhibitors of GSTs and oxygenases. Although there were no direct correlations between pyroxasulfone resistance levels and these individual parameters, a random forest analysis indicated that GST activity was of primary importance for L. rigidum resistance to this herbicide.

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.

Selective herbicide safening in dicot plants: a case study in Arabidopsis

Safeners are agrochemicals co-applied with herbicides that facilitate selective control of weeds by protecting monocot crops from chemical injury through enhancing the expression of detoxifying enzymes such as glutathione transferases (GSTs). Even though the application of safeners causes the induction of genes encoding GSTs in model dicots such as Arabidopsis thaliana, safeners do not protect broadleaf crops from herbicide injury. In this study, we proposed that the localized induction of Arabidopsis GSTs and the fundamental differences in their detoxifying activity between dicot and monocot species, underpin the failure of safeners to protect Arabidopsis from herbicide toxicity. Using the herbicide safener, isoxadifen-ethyl, we showed that three tau (U) family GSTs namely AtGSTU7, AtGSTU19 and AtGSTU24 were induced with different magnitude by isoxadifen treatment in root and rosette tissues. The higher magnitude of inducibility of these AtGSTUs in the root tissues coincided with the enhanced metabolism of flufenacet, a herbicide that is active in root tissue, protecting Arabidopsis plants from chemical injury. Assay of the recombinant enzyme activities and the significant reduction in flufenacet metabolism determined in the T-DNA insertion mutant of AtGSTU7 (gstu7) in Arabidopsis plants identified an important function for AtGSTU7 protein in flufenacet detoxification. In-silico structural modeling of AtGSTU7, suggested the unique high activity of this enzyme toward flufenacet was due to a less constrained active site compared to AtGSTU19 and AtGSTU24. We demonstrate here that it is possible to induce herbicide detoxification in dicotyledonous plants by safener treatment, albeit with this activity being restricted to very specific combinations of herbicide chemistry, and the localized induction of enzymes with specific detoxifying activities.

The function of UDP-glycosyltransferases in plants and their possible use in crop protection

Glycosyltransferases catalyse the transfer of a glycosyl moiety from a donor to an acceptor. Members of this enzyme class are ubiquitous throughout all kingdoms of life and are involved in the biosynthesis of countless types of glycosides. Family 1 glycosyltransferases, also referred to as uridine diphosphate-dependent glycosyltransferases (UGTs), glycosylate small molecules such as secondary metabolites and xenobiotics. In plants, UGTs are recognised for their multiple functionalities ranging from roles in growth regulation and development, in protection against pathogens and abiotic stresses and in adaptation to changing environments. In this study, we review UGT-mediated glycosylation of phytohormones, endogenous secondary metabolites, and xenobiotics and contextualise the role this chemical modification plays in the response to biotic and abiotic stresses and plant fitness. Here, the potential advantages and drawbacks of altering the expression patterns of specific UGTs along with the heterologous expression of UGTs across plant species to improve stress tolerance in plants are discussed. We conclude that UGT-based genetic modification of plants could potentially enhance agricultural efficiency and take part in controlling the biological activity of xenobiotics in bioremediation strategies. However, more knowledge of the intricate interplay between UGTs in plants is needed to unlock the full potential of UGTs in crop resistance.

Solvent Engineering for Nonpolar Substrate Glycosylation Catalyzed by the UDP-Glucose-Dependent Glycosyltransferase UGT71E5: Intensification of the Synthesis of 15-Hydroxy Cinmethylin β-d-Glucoside

Sugar nucleotide-dependent glycosyltransferases are powerful catalysts of the glycosylation of natural products and xenobiotics. The low solubility of the aglycone substrate often limits the synthetic efficiency of the transformation catalyzed. Here, we explored different approaches of solvent engineering for reaction intensification of β-glycosylation of 15HCM (a C15-hydroxylated, plant detoxification metabolite of the herbicide cinmethylin) catalyzed by safflower UGT71E5 using UDP-glucose as the donor substrate. Use of a cosolvent (DMSO, ethanol, and acetonitrile; ≤50 vol %) or a water-immiscible solvent (n-dodecane, n-heptane, n-hexane, and 1-hexene) was ineffective due to enzyme activity and stability, both impaired ≥10-fold compared to a pure aqueous solvent. Complexation in 2-hydroxypropyl-β-cyclodextrin enabled dissolution of 50 mM 15HCM while retaining the UGT71E5 activity (∼0.32 U/mg) and stability. Using UDP-glucose recycling, 15HCM was converted completely, and 15HCM β-d-glucoside was isolated in 90% yield (∼150 mg). Collectively, this study highlights the requirement for a mild, enzyme-compatible strategy for aglycone solubility enhancement in glycosyltransferase catalysis applied to glycoside synthesis.

Genome and whole-genome resequencing of Cinnamomum camphora elucidate its dominance in subtropical urban landscapes

BACKGROUND

Lauraceae is well known for its significant phylogenetic position as well as important economic and ornamental value; however, most evergreen species in Lauraceae are restricted to tropical regions. In contrast, camphor tree (Cinnamomum camphora) is the most dominant evergreen broadleaved tree in subtropical urban landscapes.

RESULTS

Here, we present a high-quality reference genome of C. camphora and conduct comparative genomics between C. camphora and C. kanehirae. Our findings demonstrated the significance of key genes in circadian rhythms and phenylpropanoid metabolism in enhancing cold response, and terpene synthases (TPSs) improved defence response with tandem duplication and gene cluster formation in C. camphora. Additionally, the first comprehensive catalogue of C. camphora based on whole-genome resequencing of 75 accessions was constructed, which confirmed the crucial roles of the above pathways and revealed candidate genes under selection in more popular C. camphora, and indicated that enhancing environmental adaptation is the primary force driving C. camphora breeding and dominance.

CONCLUSIONS

These results decipher the dominance of C. camphora in subtropical urban landscapes and provide abundant genomic resources for enlarging the application scopes of evergreen broadleaved trees.

Research Progress on the Action Mechanism of Herbicide Safeners: A Review

Herbicide safeners are agricultural chemicals that protect crops from herbicide injury and improve the safety of herbicides and the effectiveness of weed control. Safeners induce and enhance the tolerance of crops to herbicides through the synergism of multiple mechanisms. The principal mechanism is that the metabolic rate of the herbicide in the crop is accelerated by safeners, resulting in the damaging concentration at the site of action being reduced. We focused on discussing and summarizing the multiple mechanisms of safeners to protect crops in this review. It is also emphasized how safeners alleviate herbicide phytotoxicity to crops by regulating the detoxification process and conducting perspectives on future research on the action mechanism of safeners at the molecular level.

Metabolite modification in oxidative stress responses: A case study of two defense hormones

Studies of the Arabidopsis cat2 mutant lacking the major leaf isoform of catalase have allowed the potential impact of intracellular H₂O₂ on plant function to be studied. Here, we report a robust analysis of modified gene expression associated with key families involved in metabolite modification in cat2. Through a combined transcriptomic and metabolomic analysis focused on the salicylic acid (SA) and jasmonic acid (JA) pathways, we report key features of the metabolic signatures linked to oxidative stress-induced signaling via these defence hormones and discuss the enzymes that are likely to be involved in determining these features. We provide evidence that specific UDP-glycosyl transferases contribute to the glucosylation of SA that accumulates as a result of oxidative stress in cat2. Glycosides of dihydroxybenzoic acids that accumulate alongside SA in cat2 are identified and, based on the expression of candidate genes, likely routes for their production are discussed. We also report that enhanced intracellular H₂O₂ triggers induction of genes encoding different enzymes that can metabolize JA. Integrated analysis of metabolite and transcript profiles suggests that a gene network involving specific hydrolases, hydroxylases, and sulfotransferases functions to limit accumulation of the most active jasmonates during oxidative stress.

Detoxification of monoterpenes by a family of plant glycosyltransferases

Plant monoterpenes are challenging compounds, since they often act as solvents, and thus have both phytotoxic and antimicrobial properties. In this study an approach is developed to identify and characterize enzymes that can detoxify monoterpenoids, and thus would protect both plants and microbial production systems from these compounds. Plants respond to the presence of monoterpenes by expressing glycosyltransferases (UGTs), which conjugate the monoterpenoids into glycosides. By identifying these enzymes in a transcriptomics approach using Mentha × piperita, a family of UGTs was identified which is active on cyclic monoterpenoids such as menthol, and on acyclic monoterpenoids such as geranic acid. Other members of this family, from tomato, were also shown to be active on these monoterpenoids. In vitro and in vivo activity of different UGTs were tested with different substrates. We found that some glycosyltransferases significantly affect the toxicity of selected monoterpenoids in Escherichia coli, suggesting that glycosyltransferases can protect cells from monoterpenoid toxicity.

Glycoside-specific metabolomics combined with precursor isotopic labeling for characterizing plant glycosyltransferases

Glycosylation by uridine diphosphate-dependent glycosyltransferases (UGTs) in plants contributes to the complexity and diversity of secondary metabolites. UGTs are generally promiscuous in their use of acceptors, making it challenging to reveal the function of UGTs in vivo. Here, we described an approach that combined glycoside-specific metabolomics and precursor isotopic labeling analysis to characterize UGTs in Arabidopsis. We revisited the UGT72E cluster, which has been reported to catalyze the glycosylation of monolignols. Glycoside-specific metabolomics analysis reduced the number of differentially accumulated metabolites in the ugt72e1e2e3 mutant by at least 90% compared with that from traditional untargeted metabolomics analysis. In addition to the two previously reported monolignol glycosides, a total of 62 glycosides showed reduced accumulation in the ugt72e1e2e3 mutant, 22 of which were phenylalanine-derived glycosides, including 5-OH coniferyl alcohol-derived and lignan-derived glycosides, as confirmed by isotopic tracing of [¹³C₆]-phenylalanine precursor. Our method revealed that UGT72Es could use coumarins as substrates, and genetic evidence showed that UGT72Es endowed plants with enhanced tolerance to low iron availability under alkaline conditions. Using the newly developed method, the function of UGT78D2 was also evaluated. These case studies suggest that this method can substantially contribute to the characterization of UGTs and efficiently investigate glycosylation processes, the complexity of which have been highly underestimated.

Transcriptional response of a target plant to benzoxazinoid and diterpene allelochemicals highlights commonalities in detoxification

BACKGROUND

Plants growing in proximity to other plants are exposed to a variety of metabolites that these neighbors release into the environment. Some species produce allelochemicals to inhibit growth of neighboring plants, which in turn have evolved ways to detoxify these compounds.

RESULTS

In order to understand how the allelochemical-receiving target plants respond to chemically diverse compounds, we performed whole-genome transcriptome analysis of Arabidopsis thaliana exposed to either the benzoxazinoid derivative 2-amino- 3H-phenoxazin-3-one (APO) or momilactone B. These two allelochemicals belong to two very different compound classes, benzoxazinoids and diterpenes, respectively, produced by different Poaceae crop species.

CONCLUSIONS

Despite their distinct chemical nature, we observed similar molecular responses of A. thaliana to these allelochemicals. In particular, many of the same or closely related genes belonging to the three-phase detoxification pathway were upregulated in both treatments. Further, we observed an overlap between genes upregulated by allelochemicals and those involved in herbicide detoxification. Our findings highlight the overlap in the transcriptional response of a target plant to natural and synthetic phytotoxic compounds and illustrate how herbicide resistance could arise via pathways involved in plant-plant interaction.

Dissipation rates, residue distribution, degradation products, and degradation pathway of sulfoxaflor in broccoli

Broccoli was selected as the research object in this paper to reveal the dissipation, distribution, and degradation pathway of sulfoxaflor under greenhouse and open-field cultivation conditions for the ecological risk assessment of sulfoxaflor. Results showed that the dissipation of sulfoxaflor in broccoli leaves, flowers, stems, roots, and the whole broccoli was in accordance with the first-order kinetic equation. The sulfoxaflor concentration in broccoli roots reached the maximum value after 1 day of application and then gradually decreased. The degradation half-lives of sulfoxaflor in the roots, leaves, flowers, stems, and whole broccoli were between 2.3 and 19.8 days. The longest degradation half-life of sulfoxaflor was in Heilongjiang under greenhouse cultivation. The terminal residue of sulfoxaflor in broccoli was in the range of 0.005-0.029 mg/kg, and the proportion of sulfoxaflor residue in broccoli leaves was the largest. Thirteen transformation products were separated and identified by ultrahigh-performance liquid chromatography-quadrupole time-of-flight mass spectrometry, and their kinetic evolution was studied. The cleavage of the N = S bond, C-S bond, C-O bond, and cyanide, as well as glucosylation, hydroxylation, SO extrusion, elimination, sulfhydrylation, ketonization, defluorination, and rearrangement, was inferred as the mechanism. Overall, these results can provide guidance for the supervision of the safe application of sulfoxaflor.

Transcriptome Analysis and HPLC Profiling of Flavonoid Biosynthesis in Citrus aurantium L. during Its Key Developmental Stages

Citrus aurantium L. (sour orange) is a significant Chinese medicinal and fruit crop rich in flavonoids. However, the pathways and genes involved in flavonoid biosynthesis at the key developmental stages of Citrus aurantium L. are not fully understood. This study found that the total flavonoid concentration gradually decreased as the fruit developed. Additionally, it showed that neohesperidin was the main flavonoid in the early stages of sour orange fruit development. However, as the development stage progressed, naringin content increased rapidly and emerged as the main flavonoid component. From 27 cDNA libraries, RNA sequencing yielded 16.64 billion clean bases, including 8989 differentially expressed genes. We identified 74 flavonoid related unigenes mapped to the phenylalanine, tyrosine, and phenylpropanoid biosynthesis pathways. A total of 152 UDP-glucuronosyltransferase genes (UGTs) were identified from C. aurantium L. transcriptome database, in which 22 key flavonoid-correlated UGTs were divided into five main AtGT groups: E, G, I, L, M. We observed that the ethylene responsive factors (ERF) and myeloblastosis (MYB) family mainly regulated the key genes involved in flavonoid biosynthesis. Overall, our study generated extensive and detailed transcriptome data on the development of C. aurantium L. and characterized the flavonoid biosynthesis pattern during its fruit developmental stages. These results will benefit genetic modification or selection to increase the flavonoid content in sour oranges.

Transcriptome analysis and the identification of genes involved in the metabolic pathways of fenoxaprop-P-ethyl in rice treated with isoxadifen-ethyl hydrolysate

Fenoxaprop-P-ethyl (FE) is a highly effective weed control agent for rice fields, but it causes phytotoxicity in crops. A whole-plant bioassay has revealed that isoxadifen-ethyl hydrolysate (IH) can significantly improve the tolerance of rice to FE, but the molecular mechanisms underlying this phenomenon are still unclear. In this study, we performed RNA-Seq analysis using rice seedlings treated with FE and IH to determine the IH-regulated candidate genes involved in metabolic resistance to FE. We also analyzed spatiotemporal expression using quantitative reverse transcription polymerase chain reaction to reveal the expression patterns of these genes under different treatments. The results showed that genes encoding metabolic enzymes, such as cytochrome P450 monooxygenases, glutathione-s-transferases, UDP-glycosyltransferase, carboxylesterase, and ATP-binding cassette transporter, were influenced by the application of IH. Most of these genes were upregulated, and their products were involved in various stages of FE metabolism. Tolerance to FE was primarily mediated by CarE15, CYP86A1, GSTU6, GST4, UGT13248, UGT79, and ABCC4, all of which played a vital role in regulating the detoxification process of FE. Our findings elucidated the protective mechanisms of IH, which can help alleviate the phytotoxic effects of FE and expand its potential for application in agriculture.

UGT72, a Major Glycosyltransferase Family for Flavonoid and Monolignol Homeostasis in Plants

Simple Summary

Phenylpropanoids are specialized metabolites playing crucial roles in plant developmental processes and in plant defense towards pathogens. The attachment of sugar moieties to these small hydrophobic molecules renders them more hydrophilic and increases their solubility. The UDP-glycosyltransferase 72 family (UGT72) of plants has been shown to glycosylate mainly two classes of phenylpropanoids, (i) the monolignols that are the building blocks of lignin, the second most abundant polymer after cellulose, and (ii) the flavonoids, which play determinant roles in plant interactions with other organisms and in response to stress. The purpose of this review is to bring an overview of the current knowledge of the UGT72 family and to highlight its role in the homeostasis of these molecules. Potential applications in pharmacology and in wood, paper pulp, and bioethanol production are given within the perspectives.

Abstract

Plants have developed the capacity to produce a diversified range of specialized metabolites. The glycosylation of those metabolites potentially decreases their toxicity while increasing their stability and their solubility, modifying their transport and their storage. The UGT, forming the largest glycosyltransferase superfamily in plants, combine enzymes that glycosylate mainly hormones and phenylpropanoids by using UDP-sugar as a sugar donor. Particularly, members of the UGT72 family have been shown to glycosylate the monolignols and the flavonoids, thereby being involved in their homeostasis. First, we explore primitive UGTs in algae and liverworts that are related to the angiosperm UGT72 family and their role in flavonoid homeostasis. Second, we describe the role of several UGT72s glycosylating monolignols, some of which have been associated with lignification. In addition, the role of other UGT72 members that glycosylate flavonoids and are involved in the development and/or stress response is depicted. Finally, the importance to explore the subcellular localization of UGTs to study their roles in planta is discussed.

Controllable Iterative β-Glucosylation from UDP-Glucose by Bacillus cereus Glycosyltransferase GT1: Application for the Synthesis of Disaccharide-Modified Xenobiotics

Glycosylation in natural product metabolism and xenobiotic detoxification often leads to disaccharide-modified metabolites. The chemical synthesis of such glycosides typically separates the glycosylation steps in space and time. The option to perform the two-step glycosylation in one pot, and catalyzed by a single permissive enzyme, is interesting for a facile access to disaccharide-modified products. Here, we reveal the glycosyltransferase GT1 from Bacillus cereus (BcGT1; gene identifier: KT821092) for iterative O-β-glucosylation from uridine 5'-diphosphate (UDP)-glucose to form a β-linked disaccharide of different metabolites, including a C15 hydroxylated detoxification intermediate of the agricultural herbicide cinmethylin (15HCM). We identify thermodynamic and kinetic requirements for the selective formation of the disaccharide compared to the monosaccharide-modified 15HCM. As shown by NMR and high-resolution MS, β-cellobiosyl and β-gentiobiosyl groups are attached to the aglycone's O15 in a 2:1 ratio. Glucosylation reactions on methylumbelliferone and 4-nitrophenol involve reversible glycosyl transfer from and to UDP as well as UDP-glucose hydrolysis, both catalyzed by BcGT1. Collectively, this study delineates the iterative β-d-glucosylation of aglycones by BcGT1 and demonstrates applicability for the programmable one-pot synthesis of disaccharide-modified 15HCM.

Molecular cloning and functional characterization of UGTs from Glycyrrhiza uralensis flavonoid pathway

Glycyrrhiza uralensis Fisch., a well-known medicinal plant, contains flavonoids including liquiritigenin and isoliquiritigenin, and their corresponding glycoside liquiritin and isoliquiritin. Although some genes encoding UDP-glycosyltransferases (UGTs) have been functionally characterized in G. uralensis, other UGTs mechanisms of glycosylation remain to be elucidated. Against this background the aim of the present study included cloning and characterization of two full-length cDNA clones of GuUGT isoforms from the UGT multigene family. These included GuUGT2 (NCBI acc. MK341791) and GuUGT3 (NCBI acc. MK341793) with an ORF of 1473 and 1332 bp, respectively. Multiple alignments and phylogenetic analysis revealed GuUGTs protein of Glycine max had a high homology to that of other plants. Meanwhile, quantitative real-time PCR was performed to detect the transcript levels of GuUGTs in different tissues. The results indicated that GuUGTs was more expressed in roots as compared to the leaves, and significantly up-regulated upon NaCl stress. The recombinant protein was heterologous expressed in Escherichia coli and exhibited a high level of UGT activity, catalyzing formation of isoliquiritin and liquiritin from isoliquiritigenin and liquiritigenin. The key residues of GuUGT2 for liquiritigenin glycosylation (Asn223), isoliquiritigenin (Asp272) were predicted by molecular docking and residue scanning based on simulated mutations. These results could serve as an important reference to understand the function of the UGT family. In addition, the identification of GuUGT2 and GuUGT3 provides a foundation for future studies of flavonoid biosynthesis in G. uralensis.

Metabolism and detoxification of pesticides in plants

Pesticides make indispensable contributions to agricultural productivity. However, the residues after their excessive use may be harmful to crop production, food safety and human health. Although the ability of plants (especially crops) to accumulate and metabolize pesticides has been intensively investigated, data describing the chemical and metabolic processes in plants are limited. Understanding how pesticides are metabolized is a key step toward developing cleaner crops with minimal pesticides in crops, creating new green pesticides (or safeners), and building up the engineered plants for environmental remediation. In this review, we describe the recently discovered mechanistic insights into pesticide metabolic pathways, and development of improved plant genotypes that break down pesticides more effectively. We highlight the identification of biological features and functions of major pesticide-metabolized enzymes such as laccases, glycosyltransferases, methyltransferases and ATP binding cassette (ABC) transporters, and discuss their chemical reactions involved in diverse pathways including the formation of pesticide S-conjugates. The recent findings for some signal molecules (phytohomormes) like salicylic acid, jasmonic acid and brassinosteroids involved in metabolism and detoxification of pesticides are summarized. In particular, the emerging research on the epigenetic mechanisms such DNA methylation and histone modification for pesticide metabolism is emphasized. The review would broaden our understanding of the regulatory networks of the pesticide metabolic pathways in higher plants.

Permissive action of H2O2 mediated ClUGT75 expression for auxin glycosylation and Al3+- tolerance in watermelon

Although Al³⁺-toxicity is one of the limiting factors for crop production in acidic soils, little is known about the Al³⁺-tolerance mechanism in watermelon, a fairly acid-tolerant crop. This work aimed to identify the interaction between the H₂O₂ scavenging pathway and auxin glycosylation relevant to watermelon Al³⁺-tolerance. By analyzing expressions of hormone-related ClUGTs and antioxidant enzyme genes in Al³⁺-tolerant (ZJ) and Al³⁺-sensitive (NBT) cultivars, we identified ClUGT75s (B1, B2, and D1) and ClSOD1-2-ClCAT as crucial components associated with Al³⁺-tolerance. Al³⁺-stress significantly increased H₂O₂ content by 92.7% in NBT and 42.3% in ZJ, accompanied by less Al³⁺-, auxin (IAA and IBA), and MDA contents in ZJ than NBT. These findings coincided with significant ClSOD1-2 expression and stable dismutation activity in NBT than ZJ. Hence, higher H₂O₂ content in the root apex of NBT than ZJ correlated with a significant increase in auxin content and ClSOD1-2 up-regulation. Moreover, Al³⁺-activated ClUGT75D1 and ClUGT75B2 in ZJ coincided with no considerable change in IBA content, suggesting that glycosylation-mediated changes in IBA content might be relevant to Al³⁺-tolerance in watermelon. Furthermore, exogenous H₂O₂ and IBA indicated ClUGT75D1 modulating IBA is likely dependent on H₂O₂ background. We hypothesize that a higher H₂O₂ level in NBT represses ClUGT75, resulting in increased auxin than those in ZJ roots. Thus, excess in both H₂O₂ and auxin aggravated the inhibition of root elongation under Al³⁺-stress. Our findings provide insights on the permissive action of H₂O₂ in the mediation of auxin glycosylation by ClUGT75 in root apex for Al³⁺-tolerance in watermelon.

O-glycosyltransferases from Homo sapiens contributes to the biosynthesis of and Glycyrrhizin in Saccharomyces cerevisiae

Glycyrrhizin (GL) and Glycyrrhetic Acid 3-O-mono-β-D-glucuronide (GAMG) are the typical triterpenoid glycosides found in the root of licorice, a popular medicinal plant that exhibits diverse physiological effects and pharmacological manifestations. However, only few reports are available on the glycosylation enzymes involved in the biosynthesis of these valuable compounds with low conversion yield so far. In mammals, glycosyltransferases are involved in the phase II metabolism and may provide new solutions for us to engineer microbial strains to produce high valued compounds due to the substrate promiscuity of these glycosyltransferases. In this study, we mined the genomic databases of mammals and evaluated 22 candidate genes of O-glycosyltransferases by analyzing their catalytic potential for O-glycosylation of the native substrate, glycyrrhetinic acid (GA) for its glycodiversification. Out of 22 selected glycosyltransferases, only UGT1A1 exhibited high catalytic performance for biosynthesis of the key licorice compounds GL and GAMG. Molecular docking results proposed that the enzymatic activity of UGT1A1 was likely owing to the stable hydrogen bonding interactions and favorite conformations between the amino acid residues around substrate channels (P82~R85) and substrates. Furthermore, the complete biosynthesis pathway of GL was reconstructed in Saccharomyces cerevisiae for the first time, resulting in the production of 5.98 ± 0.47 mg/L and 2.31 ± 0.21 mg/L of GL and GAMG, respectively.

Identification and Characterization of Glucosyltransferase That Forms 1-Galloyl-β-d-Glucogallin in Canarium album L., a Functional Fruit Rich in Hydrolysable Tannins

Hydrolysable tannins (HTs) are useful secondary metabolites that are responsible for pharmacological activities and astringent taste, flavor, and quality in fruits. They are also the main polyphenols in Canarium album L. (Chinese olive) fruit, an interesting and functional fruit that has been cultivated for over 2000 years. The HT content of C. album fruit was 2.3-13 times higher than that of berries with a higher content of HT. 1-galloyl-β-d-glucose (βG) is the first intermediate and the key metabolite in the HT biosynthesis pathway. It is catalyzed by UDP-glucosyltransferases (UGTs), which are responsible for the glycosylation of gallic acid (GA) to form βG. Here, we first reported 140 UGTs in C. album. Phylogenetic analysis clustered them into 14 phylogenetic groups (A, B, D-M, P, and Q), which are different from the 14 typical major groups (A~N) of Arabidopsis thaliana. Expression pattern and correlation analysis showed that UGT84A77 (Isoform0117852) was highly expressed and had a positive correlation with GA and βG content. Prokaryotic expression showed that UGT84A77 could catalyze GA to form βG. These results provide a theoretical basis on UGTs in C. album, which will be helpful for further functional research and availability on HTs and polyphenols.

Transcriptome analysis identifies putative genes involved in triterpenoid biosynthesis in Platycodon grandiflorus

Comprehensive transcriptome analysis of different Platycodon grandiflorus tissues discovered genes related to triterpenoid saponin biosynthesis. Platycodon grandiflorus (Jacq.) A. DC. (P. grandiflorus), a traditional Chinese medicine, contains considerable triterpenoid saponins with broad pharmacological activities. Triterpenoid saponins are the major components of P. grandiflorus. Here, single-molecule real-time and next-generation sequencing technologies were combined to comprehensively analyse the transcriptome and identify genes involved in triterpenoid saponin biosynthesis in P. grandiflorus. We quantified four saponins in P. grandiflorus and found that their total content was highest in the roots and lowest in the stems and leaves. A total of 173,354 non-redundant transcripts were generated from the PacBio platform, and three full-length transcripts of β-amyrin synthase, the key synthase of β-amyrin, were identified. A total of 132,610 clean reads obtained from the DNBSEQ platform were utilised to explore key genes related to the triterpenoid saponin biosynthetic pathway in P. grandiflorus, and 96 differentially expressed genes were selected as candidates. The expression levels of these genes were verified by quantitative real-time PCR. Our reliable transcriptome data provide valuable information on the related biosynthesis pathway and may provide insights into the molecular mechanisms of triterpenoid saponin biosynthesis in P. grandiflorus.

Selective Action Mechanism of Fenclorim on Rice and Echinochloa crusgalli Is Associated with the Inducibility of Detoxifying Enzyme Activities and Antioxidative Defense

Fenclorim (Fen) is a safener developed for pretilachlor (Pre) that can protect rice from injury caused by Pre but does not lower the weed control effects of Pre. Unfortunately, the mechanism of selective action of Fen between rice and weeds, such as Echinochloa crusgalli (barnyard grass), has not been clarified. In this study, the differences in physiology, biochemistry, and gene transcription between rice and E. crusgalli response to Fen were compared. Comparing the protection effects of Fen on plant growth, it was found that Fen significantly protected rice from Pre, but did not protect E. crusgalli. The detection of malondialdehyde (MDA) content and activities of antioxidant enzymes showed that Pre induced significant oxidative damage both in rice and E. crusgalli; however, Fen reduced oxidative damage in rice but not in E. crusgalli. Transcriptome analysis revealed that Fen induced more genes related to herbicide metabolism in rice than in E. crusgalli, especially the glutathione-S-transferase (GST) genes, with six upregulated in rice but no genes upregulated in E. crusgalli. Accordingly, the GST activity analysis showed that Fen increased the activity of rice instead of E. crusgalli. These results indicate that the elevation of detoxifying enzyme activities and antioxidative defense may be the mechanism of selective action of Fen in rice but not in E. crusgalli.

Roles of Alkaline Phosphatase PhoA in Algal Metabolic Regulation under Phosphorus-replete Conditions

Alkaline phosphatase (AP) in plants and algae is known to hydrolyze dissolved organophosphate (DOP) in order to obtain phosphorus when the preferred dissolved inorganic phosphorus (DIP) is present in limited supply. By conducting comparative analyses of physiologies and transcriptomes on a mutant of PhoA type AP (mPhoA) and wild type (WT) of the marine diatom Phaeodactylum tricornutum CCAP 1055/1 under P-replete and P-depleted conditions, we document other roles of this gene than DOP scavenging. PhoA mutation created by CRISPR/Cas9 diminished its DOP hydrolase activity but led to significant increases in cellular contents of pigment, carbon, and lipids, photosynthetic rate, growth rate, and the transcriptional levels of their corresponding metabolic pathways. All the results in concert indicate that besides P-nutrient scavenging under DIP deficiency, AP also functions, under the P-replete condition, to constrain pigment biosynthesis, photosynthesis, fatty acid biosynthesis, and cell division. These functions have important implications in maintaining metabolic homeostasis and preventing premature cell division.

Fragments recombination, design, synthesis, safener activity and CoMFA model of novel substituted dichloroacetylphenyl sulfonamide derivatives

BACKGROUND

Isoxaflutole (IXF), as a kind of 4-hydroxyphenylpyruvate dioxygenase (HPPD) inhibitor, has been widely used in many kinds of plants. IXF can cause injury in corn including leaf and stem bleaching, plant height reduction or stunting, and reduced crop stand. Safeners are co-applied with herbicides to protect crops without compromising weed control efficacy. With the ultimate goal of addressing Zea mays injury caused by IXF, a series of novel substituted dichloroacetylphenyl sulfonamide derivatives was designed on the basis of scaffold hopping and active substructure splicing.

RESULTS

A total of 35 compounds were synthesized via acylation reactions. All the compounds were characterized by infrared (IR), proton and carbon-13 nuclear magnetic resonance (¹ H-NMR and ¹³ C-NMR), and high-resolution mass spectrometry (HRMS). The configuration of compound II-1 was confirmed by single crystal X-ray diffraction. The bioassay results showed that all the title compounds displayed remarkable protection against IXF via improved content of carotenoid. Especially compound II-1 which possessed better glutathione transferases (GSTs) activity and carotenoid content than the contrast safener cyprosulfamide (CSA). All the satisfied parameters suggested that the Comparative Molecular Field Analysis (CoMFA) model was reliable and stable [with a cross-validated coefficient (q² ) = 0.527, r² = 0.995, r² _pred = 0.931]. The molecular docking simulation indicated that the compound II-1 and CSA could compete with diketonitrile (DKN) at the active site of HPPD, which is a hydrolyzed product of IXF in plants, causing the herbicide to be ineffective.

CONCLUSIONS

The present work revealed that the compound II-1 deserves further attention as the candidate structure of safeners. © 2020 Society of Chemical Industry.

Advance in Methodology and Strategies To Unveil Metabolic Mechanisms of Pesticide Residues in Food Crops

Pesticide residues are a food safety concern. A good detection method is critical for rapid and accurate determination of pesticide metabolites in crops and studying metabolism. The pretreatment methods have mainly been ultrasonic extraction-solid-phase extraction and QuEChERS, while detection methods have been radio-chromatography, nuclear magnetic resonance, and mass spectrometry. This perspective briefed the progress of analytical methods used for studying pesticide transformation in crops over the past decade. With the combination of the characteristics of the pesticide molecular structure and the transformation principles of pesticides in crops, we presented specific methods for elucidating new metabolites and the approaches to identify metabolites using multi-high-resolution mass spectrometry.

Safening activity and metabolism of the safener cyprosulfamide in maize and wheat

BACKGROUND

Safeners extend the application of existing herbicides by selectively enhancing tolerance in large-grained cereal crops. While their activity is linked to enhanced herbicide metabolism, their exact mode of action and reasons for their crop specificity have yet to be determined. In this study, we investigated the selectivity of the recently developed sulfonamide safener cyprosulfamide (CSA) in maize (Zea mays L.) and wheat (Triticum aestivum), focusing on its uptake, distribution and metabolism in the two species.

RESULTS

CSA protected maize, but not wheat, from injury by thiencarbazone-methyl (TCM). This correlated with the selective enhanced detoxification of the herbicide in maize. CSA underwent more rapid metabolism in maize than in wheat, with the formation of a specific hydroxylated metabolite correlating with safening. Studies with the nsf1 mutant sweetcorn line showed that the hydroxylation of CSA was partly mediated by the cytochrome P450 CYP81A9. However, primary metabolites of CSA were chemically synthesised and tested for their ability to safen TCM in maize but when tested were inactive as safeners.

CONCLUSION

The results of this study suggest that the protection against TCM injury by CSA is linked to enhanced herbicide metabolism. This selective activity is due to the specific recognition of parent CSA in maize but not in wheat. Subsequent rapid oxidative metabolism of CSA led to its inactivation, demonstrating that cytochrome P450s regulate the activity of safeners as well as herbicides. © 2020 Society of Chemical Industry.

Engineering Critical Enzymes and Pathways for Improved Triterpenoid Biosynthesis in Yeast

Triterpenoids represent a diverse group of phytochemicals that are widely distributed in the plant kingdom and have many biological activities. The heterologous production of triterpenoids in Saccharomyces cerevisiae has been successfully implemented by introducing various triterpenoid biosynthetic pathways. By engineering related enzymes as well as through yeast metabolism, the yield of various triterpenoids is significantly improved from the milligram per liter scale to the gram per liter scale. This achievement demonstrates that engineering critical enzymes is considered a potential strategy to overcome the main hurdles of the industrial application of these potent natural products. Here, we review strategies for designing enzymes to improve the yield of triterpenoids in S. cerevisiae in terms of three main aspects: 1, elevating the supply of the precursor 2,3-oxidosqualene; 2, optimizing triterpenoid-involved reactions; and 3, lowering the competition of the native sterol pathway. Then, we provide challenges and prospects for further enhancing triterpenoid production in S. cerevisiae.

Functional analysis of a novel C-glycosyltransferase in the orchid Dendrobium catenatum

Flavonoids, which are a diverse class of phytonutrients, are used by organisms to respond to nearly all abiotic stresses and are beneficial for human health. Glycosyltransferase, used during the last step of flavonoid biosynthesis, is important in flavonoid enrichment. However, little is known about glycosyltransferase in the orchid Dendrobium catenatum (D. officinale). In this study, we isolated a novel C-glycosyltransferase (designated DcaCGT) from the orchid D. catenatum by identifying and analyzing 82 putative genes in the GT1 family. DcaCGT could specifically catalyze not only di-C-glycosylation but also O-glycosylation. Apart from the normal function of catalyzing 2-hydroxynaringenin and phloretin to the respective di-C-glycosides, DcaCGT also catalyzes apigenin to cosmosiin. Targeted metabolic profiling of the substrates (2-hydroxynaringenin, phloretin, and apigenin) and products (vitexin, isovitexin, vicenin-2, nothofagin, 3',5'-di-C-glucosylphloretin, and cosmosiin) in different tissues showed that vicenin-2 was the most abundant product of this novel enzyme. Cosmosiin was detected in flowers and flower buds. We also established that DcaCGT functions expanded throughout the evolution of D. catenatum. Residual OGT activity may help D. catenatum resist drought stress. Our study illustrates the function, origin, and differentiation of DcaCGT and provides insights into glycosylation and molecular propagation processes, which can be used to improve the production of flavonoids by the cultivated medicinal plant D. catenatum.

Effects of fenclorim on rice physiology, gene transcription and pretilachlor detoxification ability

BACKGROUND

Fenclorim (Fen) can effectively protect rice from pretilachlor (Pre) injury, but its effects on rice have not been formally evaluated; thus, the Fen mode of action for alleviating the phytotoxicity caused by Pre in rice is not clear. This study aimed to examine the biochemical and physiological effects of Fen on rice and to determine the changes induced by Fen at the transcriptome level.

RESULT

The chlorophyll content of rice plants was significantly affected by Pre but not by Fen. The activity of oxidative stress enzymes showed that Fen did not elicit any changes in oxidative stress; however, it reduced lipid peroxidation and oxidative damage induced by Pre. Fen did not affect the uptake of Pre but did affect its persistence in rice. In a transcriptome experiment, Fen upregulated genes in a detoxification pathway. Overall, 25 genes related to detoxification were identified, including P450, GST, and GT. Moreover, qRT-PCR analysis showed that four P450 genes, CYP71Y83, CYP71K14, CYP734A2 and CYP71D55, and two GST genes, GSTU16 and GSTF5, were upregulated by Fen and/or Pre.

CONCLUSION

Our work indicates that Fen acts in antioxidative defense in addition to enhancing the metabolism of herbicides in rice.

Phytoremediation and detoxification of xenobiotics in plants: herbicide-safeners as a tool to improve plant efficiency in the remediation of polluted environments. A mini-review

Phytoremediation is a widely studied and applied technology, based on the use of plants and their associated microorganisms to decontaminate polluted sites. In recent years, different strategies have been investigated to improve the phytoremediation efficiency of the selected plants. In this context, some studies have shown that herbicide-safeners, chemicals applied to crops to enhance their tolerance to herbicides, can increase the phytoremediation of soils and water polluted by organic and inorganic contaminants. Safeners, by inducing the xenobiotic detoxification and the antioxidant metabolism in plants, can enhance their removal potential in the cleaning process. In this review, after a short survey of phytoremediation technologies and the biochemical mechanisms activated by plants to tolerate and detoxify heavy metals and herbicides, the use of herbicide-safeners as a tool to increase the phytoremediation performance is reviewed and discussed.

Identification of Differentially Expressed Proteins in Sugarcane in Response to Infection by Xanthomonas albilineans Using iTRAQ Quantitative Proteomics

Sugarcane can suffer severe yield losses when affected by leaf scald, a disease caused by Xanthomonas albilineans. This bacterial pathogen colonizes the vascular system of sugarcane, which can result in reduced plant growth and plant death. In order to better understand the molecular mechanisms involved in the resistance of sugarcane to leaf scald, a comparative proteomic study was performed with two sugarcane cultivars inoculated with X. albilineans: one resistant (LCP 85-384) and one susceptible (ROC20) to leaf scald. The iTRAQ (isobaric tags for relative and absolute quantification) approach at 0 and 48 h post-inoculation (hpi) was used to identify and annotate differentially expressed proteins (DEPs). A total of 4295 proteins were associated with 1099 gene ontology (GO) terms by GO analysis. Among those, 285 were DEPs during X. albilineans infection in cultivars LCP 85-384 and ROC20. One hundred seventy-two DEPs were identified in resistant cultivar LCP 85-384, and 113 of these proteins were upregulated and 59 were downregulated. One hundred ninety-two DEPs were found in susceptible cultivar ROC20 and half of these (92) were upregulated, whereas the other half corresponded to downregulated proteins. The significantly upregulated DEPs in LCP 85-384 were involved in metabolic pathways, the biosynthesis of secondary metabolites, and the phenylpropanoid biosynthesis pathway. Additionally, the expression of seven candidate genes related to photosynthesis and glycolytic pathways, plant innate immune system, glycosylation process, plant cytochrome P450, and non-specific lipid transfer protein was verified based on transcription levels in sugarcane during infection by X. albilineans. Our findings shed new light on the differential expression of proteins in sugarcane cultivars in response to infection by X. albilineans. The identification of these genes provides important information for sugarcane variety improvement programs using molecular breeding strategies.

Chemically induced herbicide tolerance in rice by the safener metcamifen is associated with a phased stress response

The closely related sulphonamide safeners, metcamifen and cyprosulfamide, were tested for their ability to protect rice from clodinafop-propargyl, a herbicide normally used in wheat. While demonstrating that both compounds were equally bioavailable in planta, only metcamifen prevented clodinafop from damaging seedlings, and this was associated with the enhanced detoxification of the herbicide. Transcriptome studies in rice cultures demonstrated that whereas cyprosulfamide had a negligible effect on gene expression over a 4 h exposure, metcamifen perturbed the abundance of 590 transcripts. Changes in gene expression with metcamifen could be divided into three phases, corresponding to inductions occurring over 30 min, 1.5 h and 4 h. The first phase of gene induction was dominated by transcription factors and proteins of unknown function, the second by genes involved in herbicide detoxification, while the third was linked to cellular homeostasis. Analysis of the inducible genes suggested that safening elicited similar gene families to those associated with specific biotic and abiotic stresses, notably those elicited by abscisic acid, salicylic acid, and methyl jasmonate. Subsequent experiments with safener biomarker genes induced in phase 1 and 2 in rice cell cultures provided further evidence of similarities in signalling processes elicited by metcamifen and salicylic acid.

Enzymatic O-Glycosylation of Etoposide Aglycone by Exploration of the Substrate Promiscuity for Glycosyltransferases

The 4-O-β-d-glucopyranoside of DMEP ((-)-4'-desmethylepipodophyllotoxin) (GDMEP), a natural product from Podophyllum hexandrum, is the direct precursor to the topoisomerase inhibitor etoposide, used in dozens of chemotherapy regimens for various malignancies. The biosynthesis pathway for DMEP has been completed, while the enzyme for biosynthesizing GDMEP is still unclear. Here, we report the enzymatic O-glycosylation of DMEP with 53% conversion by exploring the substrate promiscuity and entrances of glycosyltransferases. Notably, we found 6 essential amino acid residues surrounding the putative substrate entrances exposed to the protein surface in UGT78D2, CsUGT78D2, and CsUGT78D2-like, and these residues may determine substrate specificity and high O-glycosylation activity toward DMEP. Our results provide an effective route for one-step synthesis of GDMEP. Identification of the key residues and entrances of glycosyltransferases will promote precise identification of glycosyltransferase biocatalysts for novel substrates and provide a rational basis for glycosyltransferase engineering.

A noncanonical vacuolar sugar transferase required for biosynthesis of antimicrobial defense compounds in oat

Plants produce an array of natural products with important ecological functions. These compounds are often decorated with oligosaccharide groups that influence bioactivity, but the biosynthesis of such sugar chains is not well understood. Triterpene glycosides (saponins) are a large family of plant natural products that determine important agronomic traits, as exemplified by avenacins, antimicrobial defense compounds produced by oats. Avenacins have a branched trisaccharide moiety consisting of l-arabinose linked to 2 d-glucose molecules that is critical for antifungal activity. Plant natural product glycosylation is usually performed by uridine diphosphate-dependent glycosyltransferases (UGTs). We previously characterized the arabinosyltransferase that initiates the avenacin sugar chain; however, the enzymes that add the 2 remaining d-glucose molecules have remained elusive. Here we characterize the enzymes that catalyze these last 2 glucosylation steps. AsUGT91G16 is a classical cytosolic UGT that adds a 1,2-linked d-glucose molecule to l-arabinose. Unexpectedly, the enzyme that adds the final 1,4-linked d-glucose (AsTG1) is not a UGT, but rather a sugar transferase belonging to Glycosyl Hydrolase family 1 (GH1). Unlike classical UGTs, AsTG1 is vacuolar. Analysis of oat mutants reveals that AsTG1 corresponds to Sad3, a previously uncharacterized locus shown by mutation to be required for avenacin biosynthesis. AsTG1 and AsUGT91G16 form part of the avenacin biosynthetic gene cluster. Our demonstration that a vacuolar transglucosidase family member plays a critical role in triterpene biosynthesis highlights the importance of considering other classes of carbohydrate-active enzymes in addition to UGTs as candidates when elucidating pathways for the biosynthesis of glycosylated natural products in plants.

The Sweet Side of Plant-Specialized Metabolism

Glycosylation plays a major role in the structural diversification of plant natural products. It influences the properties of molecules by modifying the reactivity and solubility of the corresponding aglycones, so influencing cellular localization and bioactivity. Glycosylation of plant natural products is usually carried out by uridine diphosphate(UDP)-dependent glycosyltransferases (UGTs) belonging to the carbohydrate-active enzyme glycosyltransferase 1 (GT1) family. These enzymes transfer sugars from UDP-activated sugar moieties to small hydrophobic acceptor molecules. Plant GT1s generally show high specificity for their sugar donors and recognize a single UDP sugar as their substrate. In contrast, they are generally promiscuous with regard to acceptors, making them attractive biotechnological tools for small molecule glycodiversification. Although microbial hosts have traditionally been used for heterologous engineering of plant-derived glycosides, transient plant expression technology offers a potentially disruptive platform for rapid characterization of new plant glycosyltransferases and biosynthesis of complex glycosides.

Phylogenomic analysis of UDP-dependent glycosyltransferases provides insights into the evolutionary landscape of glycosylation in plant metabolism

Glycosylated metabolites generated by UDP-dependent glycosyltransferases (UGTs) play critical roles in plant interactions with the environment as well as human and animal nutrition. The evolution of plant UGTs has previously been explored, but with a limited taxon sampling. In this study, 65 fully sequenced plant genomes were analyzed, and stringent criteria for selection of candidate UGTs were applied to ensure a more comprehensive taxon sampling and reliable sequence inclusion. In addition to revealing the overall evolutionary landscape of plant UGTs, the phylogenomic analysis also resolved the phylogenetic association of UGTs from free-sporing plants and gymnosperms, and identified an additional UGT group (group R) in seed plants. Furthermore, lineage-specific expansions and contractions of UGT groups were detected in angiosperms, with the total number of UGTs per genome remaining constant generally. The loss of group Q UGTs in Poales and Brassicales, rather than functional convergence in the group Q containing species, was supported by a gene tree of group Q UGTs sampled from many species, and further corroborated by the absence of group Q homologs on the syntenic chromosomal regions in Arabidopsis thaliana (Brassicales). Branch-site analyses of the group Q UGT gene tree allowed for identification of branches and amino acid sites that experienced episodic positive selection. The positively selected sites are located on the surface of a representative group Q UGT (PgUGT95B2), away from the active site, suggesting their role in protein folding/stability or protein-protein interactions.

Plant triterpenoid saponins: biosynthesis, in vitro production, and pharmacological relevance

The saponins are a diverse class of natural products, with a broad scale distribution across different plant species. Chemically characterized as triterpenoid glycosides, they posses a 30C oxidosqualene precursor-based aglycone moiety (sapogenin), to which glycosyl residues are subsequently attached to yield the corresponding saponin. Based on the chemically distinct aglycone moieties, broadly, they are divided into triterpenoid saponins (dammaranes, ursanes, oleananes, lupanes, hopanes, etc.) and the sterol glycosides. This review aims to present in detail the biosynthesis patterns of the different aglycones from a common precursor and their glycosylation patterns to yield the functionally active glycoside. The review also presents recent advances in the pharmacological activities of these saponins, particularly as potent anti-neoplastic pharmacophores, antioxidants, or anti-viral/antibacterial agents. Since alternate production pedestals for these pharmacologically important triterpenes via cell and tissue cultures are an attractive option for their sustainable production, recent trends in the variety and scale of in vitro production of plant triterpenoids have also been discussed.

Exploring the Phytochemical Landscape of the Early-Diverging Flowering Plant Amborella trichopoda Baill

Although the evolutionary significance of the early-diverging flowering plant Amborella (Amborella trichopoda Baill.) is widely recognized, its metabolic landscape, particularly specialized metabolites, is currently underexplored. In this work, we analyzed the metabolomes of Amborella tissues using liquid chromatography high-resolution electrospray ionization mass spectrometry (LC-HR-ESI-MS). By matching the mass spectra of Amborella metabolites with those of authentic phytochemical standards in the publicly accessible libraries, 63, 39, and 21 compounds were tentatively identified in leaves, stems, and roots, respectively. Free amino acids, organic acids, simple sugars, cofactors, as well as abundant glycosylated and/or methylated phenolic specialized metabolites were observed in Amborella leaves. Diverse metabolites were also detected in stems and roots, including those that were not identified in leaves. To understand the biosynthesis of specialized metabolites with glycosyl and methyl modifications, families of small molecule UDP-dependent glycosyltransferases (UGTs) and O-methyltransferases (OMTs) were identified in the Amborella genome and the InterPro database based on conserved functional domains. Of the 17 phylogenetic groups of plant UGTs (A–Q) defined to date, Amborella UGTs are absent from groups B, N, and P, but they are highly abundant in group L. Among the 25 Amborella OMTs, 7 cluster with caffeoyl-coenzyme A (CCoA) OMTs involved in lignin and phenolic metabolism, whereas 18 form a clade with plant OMTs that methylate hydroxycinnamic acids, flavonoids, or alkaloids. Overall, this first report of metabolomes and candidate metabolic genes in Amborella provides a starting point to a better understanding of specialized metabolites and biosynthetic enzymes in this basal lineage of flowering plants.

Diversity of O-Glycosyltransferases Contributes to the Biosynthesis of Flavonoid and Triterpenoid Glycosides in Glycyrrhiza uralensis

Licorice (Glycyrrhiza uralensis) is a popular medicinal plant containing more than 70 flavonoid and triterpenoid glycosides. Thus far, only a few reports are available on the glycosylation enzymes involved in their biosynthesis. In this work, we mined the transcriptome data of G. uralensis and discovered 43 candidate genes for O-glycosyltransferase (O-GT). Among them, 17 genes could be expressed in E. coli, and functions of the enzymes were analyzed by catalyzing eight native substrates. As a result, we characterized 11 O-GTs, including isoflavone 7-O-GTs, flavonol 3-O-GTs, and promiscuous O-GTs catalyzing flavones, chalcones, and triterpenoids. They could efficiently synthesize key licorice compounds such as liquiritin, isoliquiritin, ononin, and 3-O-β-d-glucuronosyl glycyrrhetinic acid. The diversity of O-GTs contributes to the biosynthesis of various glycosides in licorice. These enzymes could also be used as biocatalytic tools to synthesize other bioactive O-glycosides.

Triterpenoid-biosynthetic UDP-glycosyltransferases from plants

Triterpenoid saponins are naturally occurring structurally diverse glycosides of triterpenes that are widely distributed among plant species. Great interest has been expressed by pharmaceutical and agriculture industries for the glycosylation of triterpenes. Such modifications alter their taste and bio-absorbability, affect their intra-/extracellular transport and storage in plants, and induce novel biological activities in the human body. Uridine diphosphate (UDP)-glycosyltransferases (UGTs) catalyze glycosylation using UDP sugar donors. These enzymes belong to a multigene family and recognize diverse natural products, including triterpenes, as the acceptor molecules. For this review, we collected and analyzed all of the UGT sequences found in Arabidopsis thaliana as well as 31 other species of triterpene-producing plants. To identify potential UGTs with novel functions in triterpene glycosylation, we screened and classified those candidates based on similarity with UGTs from Panax ginseng, Glycine max, Medicago truncatula, Saponaria vaccaria, and Barbarea vulgaris that are known to function in glycosylate triterpenes. We highlight recent findings on UGT inducibility by methyl jasmonate, tissue-specific expression, and subcellular localization, while also describing their catalytic activity in terms of regioselectivity for potential key UGTs dedicated to triterpene glycosylation in plants. Discovering these new UGTs expands our capacity to manipulate the biological and physicochemical properties of such valuable molecules.

Testing a chemical series inspired by plant stress oxylipin signalling agents for herbicide safening activity

BACKGROUND

Herbicide safening in cereals is linked to a rapid xenobiotic response (XR), involving the induction of glutathione transferases (GSTs). The XR is also invoked by oxidized fatty acids (oxylipins) released during plant stress, suggesting a link between these signalling agents and safening. To examine this relationship, a series of compounds modelled on the oxylipins 12-oxophytodienoic acid and phytoprostane 1, varying in lipophilicity and electrophilicity, were synthesized. Compounds were then tested for their ability to invoke the XR in Arabidopsis and protect rice seedlings exposed to the herbicide pretilachlor, as compared with the safener fenclorim.

RESULTS

Of the 21 compounds tested, three invoked the rapid GST induction associated with fenclorim. All compounds possessed two electrophilic carbon centres and a lipophilic group characteristic of both oxylipins and fenclorim. Minor effects observed in protecting rice seedlings from herbicide damage positively correlated with the XR, but did not provide functional safening.

CONCLUSION

The design of safeners based on the characteristics of oxylipins proved successful in deriving compounds that invoke a rapid XR in Arabidopsis but not in providing classical safening in a cereal. The results further support a link between safener and oxylipin signalling, but also highlight species-dependent differences in the responses to these compounds. © 2018 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Phenylpropanoid Scent Compounds in Petunia x hybrida Are Glycosylated and Accumulate in Vacuoles

Floral scent has been studied extensively in the model plant Petunia. However, little is known about the intracellular fate of scent compounds. Here, we characterize the glycosylation of phenylpropanoid scent compounds in Petunia x hybrida. This modification reduces scent compounds' volatility, reactivity, and autotoxicity while increasing their water-solubility. Gas chromatography-mass spectrometry (GC-MS) analyses revealed that flowers of petunia cultivars accumulate substantial amounts of glycosylated scent compounds and that their increasing level parallels flower development. In contrast to the pool of accumulated aglycones, which drops considerably at the beginning of the light period, the collective pool of glycosides starts to increase at that time and does not decrease thereafter. The glycoside pool is dynamic and is generated or catabolized during peak scent emission, as inferred from phenylalanine isotope-feeding experiments. Using several approaches, we show that phenylpropanoid scent compounds are stored as glycosides in the vacuoles of petal cells: ectopic expression of Aspergillus niger β-glucosidase-1 targeted to the vacuole resulted in decreased glycoside accumulation; GC-MS analysis of intact vacuoles isolated from petal protoplasts revealed the presence of glycosylated scent compounds. Accumulation of glycosides in the vacuoles seems to be a common mechanism for phenylpropanoid metabolites.