Glycosyltransferases: managers of small molecules

UGT84F9 is the major flavonoid UDP-glucuronosyltransferase in Medicago truncatula

Mammalian phase II metabolism of dietary plant flavonoid compounds generally involves substitution with glucuronic acid. In contrast, flavonoids mainly exist as glucose conjugates in plants, and few plant UDP-glucuronosyltransferase enzymes have been identified to date. In the model legume Medicago truncatula, the major flavonoid compounds in the aerial parts of the plant are glucuronides of the flavones apigenin and luteolin. Here we show that the M. truncatula glycosyltransferase UGT84F9 is a bi-functional glucosyl/glucuronosyl transferase in vitro, with activity against a wide range of flavonoid acceptor molecules including flavones. However, analysis of metabolite profiles in leaves and roots of M. truncatula ugt84f9 loss of function mutants revealed that the enzyme is essential for formation of flavonoid glucuronides, but not most flavonoid glucosides, in planta. We discuss the use of plant UGATs for the semi-synthesis of flavonoid phase II metabolites for clinical studies.

Evolutionary diversification of cytokinin-specific glucosyltransferases in angiosperms and enigma of missing cis-zeatin O-glucosyltransferase gene in Brassicaceae

In the complex process of homeostasis of phytohormones cytokinins (CKs), O-glucosylation catalyzed by specific O-glucosyltransferases represents one of important mechanisms of their reversible inactivation. The CK O-glucosyltransferases belong to a highly divergent and polyphyletic multigene superfamily of glycosyltransferases, of which subfamily 1 containing UDP-glycosyltransferases (UGTs) is the largest in the plant kingdom. It contains recently discovered O and P subfamilies present in higher plant species but not in Arabidopsis thaliana. The cis-zeatin O-glucosyltransferase (cisZOG) genes belong to the O subfamily encoding a stereo-specific O-glucosylation of cis-zeatin-type CKs. We studied different homologous genes, their domains and motifs, and performed a phylogenetic reconstruction to elucidate the plant evolution of the cisZOG gene. We found that the cisZOG homologs do not form a clear separate clade, indicating that diversification of the cisZOG gene took place after the diversification of the main angiosperm families, probably within genera or closely related groups. We confirmed that the gene(s) from group O is(are) not present in A. thaliana and is(are) also missing in the family Brassicaceae. However, cisZOG or its metabolites are found among Brassicaceae clade, indicating that remaining genes from other groups (UGT73-group D and UGT85-group G) are able, at least in part, to substitute the function of group O lost during evolution. This study is the first detailed evolutionary evaluation of relationships among different plant ZOGs within angiosperms.

Enzymatic basis for stepwise C-glycosylation in the formation of flavonoid di-C-glycosides in sacred lotus (Nelumbo nucifera Gaertn.)

Lotus plumule, the embryo of the seed of the sacred lotus (Nelumbo nucifera), contains a high accumulation of secondary metabolites including flavonoids and possesses important pharmaceutical value. Flavonoid C-glycosides, which accumulate exclusively in lotus plumule, have attracted considerable attention in recent decades due to their unique chemical structure and special bioactivities. As well as mono-C-glycosides, lotus plumule also accumulates various kinds of di-C-glycosides by mechanisms which are as yet unclear. In this study we identified two C-glycosyltransferase (CGT) genes by mining sacred lotus genome data and provide in vitro and in planta evidence that these two enzymes (NnCGT1 and NnCGT2, also designated as UGT708N1 and UGT708N2, respectively) exhibit CGT activity. Recombinant UGT708N1 and UGT708N2 can C-glycosylate 2-hydroxyflavanones and 2-hydroxynaringenin C-glucoside, forming flavone mono-C-glycosides and di-C-glycosides, respectively, after dehydration. In addition, the above reactions were successfully catalysed by cell-free extracts from tobacco leaves transiently expressing NnCGT1 or NnCGT2. Finally, enzyme assays using cell-free extracts of lotus plumule suggested that flavone di-C-glycosides (vicenin-1, vicenin-3, schaftoside and isoschaftoside) are biosynthesized through sequentially C-glucosylating and C-arabinosylating/C-xylosylating 2-hydroxynaringenin. Taken together, our results provide novel insights into the biosynthesis of flavonoid di-C-glycosides by proposing a new biosynthetic pathway for flavone C-glycosides in N. nucifera and identifying a novel uridine diphosphate-glycosyltransferase (UGT708N2) that specifically catalyses the second glycsosylation, C-arabinosylating and C-xylosylating 2-hydroxynaringenin C-glucoside.

Iris domestica (iso)flavone 7- and 3'-O-Glycosyltransferases Can Be Induced by CuCl2

In many plants, isoflavones are the main secondary metabolites that have various pharmacological activities, but the low water solubility of aglycones limits their usage. The O-glycosylation of (iso)flavones is a promising way to overcome this barrier. O-glycosyltransferases (UGTs) are key enzymes in the biosynthesis of (iso)flavonoid O-glycosides in plants. However, limited investigations on isoflavonoid O-UGTs have been reported, and they mainly focused on legumes. Iris domestica (L.) Goldblatt et Mabberley is a non-legume plant rich in various isoflavonoid glycosides. However, there are no reports regarding its glycosylation mechanism, despite the I. domestica transcriptome previously being annotated as having non-active isoflavone 7-O-UGTs. Our previous experiments indicated that isoflavonoid glycosides were induced by CuCl₂ in I. domestica calli; therefore, we hypothesized that isoflavone O-UGTs may be induced by Cu²⁺. Thus, a comparative transcriptome analysis was performed using I. domestica seedlings treated with CuCl₂, and eight new active BcUGTs were obtained. Biochemical analyses showed that most of the active BcUGTs had broad substrate spectra; however, substrates lacking 5-OH were rarely catalyzed. Real-time quantitative PCR results further indicated that the transcriptional levels of BcUGTs were remarkably induced by Cu²⁺. Our study increases the understanding of UGTs and isoflavone biosynthesis in non-legume plants.

Non-target-Site Resistance in Lolium spp. Globally: A Review

The Lolium genus encompasses many species that colonize a variety of disturbed and non-disturbed environments. Lolium perenne L. spp. perenne, L. perenne L. spp. multiflorum, and L. rigidum are of particular interest to weed scientists because of their ability to thrive in agricultural and non-agricultural areas. Herbicides are the main tool to control these weeds; however, Lolium spp. populations have evolved multiple- and cross-resistance to at least 14 herbicide mechanisms of action in more than 21 countries, with reports of multiple herbicide resistance to at least seven mechanisms of action in a single population. In this review, we summarize what is currently known about non-target-site resistance in Lolium spp. to acetyl CoA carboxylase, acetohydroxyacid synthase, microtubule assembly, photosystem II, 5-enolpyruvylshikimate-3-phosphate synthase, glutamine synthetase, very-long chain fatty acids, and photosystem I inhibitors. We suggest research topics that need to be addressed, as well as strategies to further our knowledge and uncover the mechanisms of non-target-site resistance in Lolium spp.

Arachis hypogaea resveratrol synthase 3 alters the expression pattern of UDP-glycosyltransferase genes in developing rice seeds

The resveratrol-producing rice (Oryza sativa L.) inbred lines, Iksan 515 (I.515) and Iksan 526 (I.526), developed by the expression of the groundnut (Arachis hypogaea) resveratrol synthase 3 (AhRS3) gene in the japonica rice cultivar Dongjin, accumulated both resveratrol and its glucoside, piceid, in seeds. Here, we investigated the effect of the AhRS3 transgene on the expression of endogenous piceid biosynthesis genes (UGTs) in the developing seeds of the resveratrol-producing rice inbred lines. Ultra-performance liquid chromatography (UPLC) analysis revealed that I.526 accumulates significantly higher resveratrol and piceid in seeds than those in I.515 seeds and, in I.526 seeds, the biosynthesis of resveratrol and piceid reached peak levels at 41 days after heading (DAH) and 20 DAH, respectively. Furthermore, RNA-seq analysis showed that the expression patterns of UGT genes differed significantly between the 20 DAH seeds of I.526 and those of Dongjin. Quantitative real-time PCR (RT-qPCR) analyses confirmed the data from RNA-seq analysis in seeds of Dongjin, I.515 and I.526, respectively, at 9 DAH, and in seeds of Dongjin and I.526, respectively, at 20 DAH. A total of 245 UGTs, classified into 31 UGT families, showed differential expression between Dongjin and I.526 seeds at 20 DAH. Of these, 43 UGTs showed more than 2-fold higher expression in I.526 seeds than in Dongjin seeds. In addition, the expression of resveratrol biosynthesis genes (PAL, C4H and 4CL) was also differentially expressed between Dongjin and I.526 developing seeds. Collectively, these data suggest that AhRS3 altered the expression pattern of UGT genes, and PAL, C4H and 4CL in developing rice seeds.

The ectopic expression of Arabidopsis glucosyltransferase UGT74D1 affects leaf positioning through modulating indole-3-acetic acid homeostasis

Leaf angle is an important agronomic trait affecting photosynthesis efficiency and crop yield. Although the mechanisms involved in the leaf angle control are intensively studied in monocots, factors contribute to the leaf angle in dicots are largely unknown. In this article, we explored the physiological roles of an Arabidopsis glucosyltransferase, UGT74D1, which have been proved to be indole-3-acetic acid (IAA) glucosyltransferase in vitro. We found that UGT74D1 possessed the enzymatic activity toward IAA glucosylation in vivo and its expression was induced by auxins. The ectopically expressed UGT74D1 obviously reduced the leaf angle with an altered IAA level, auxin distribution and cell size in leaf tissues. The expression of several key genes involved in the leaf shaping and leaf positioning, including PHYTOCHROME KINASE SUBSTRATE (PKS) genes and TEOSINTE BRANCHED1, CYCLOIDEA, and PCF (TCP) genes, were dramatically changed by ectopic expression of UGT74D1. In addition, clear transcription changes of YUCCA genes and other auxin related genes can be observed in overexpression lines. Taken together, our data indicate that glucosyltransferase UGT74D1 could affect leaf positioning through modulating auxin homeostasis and regulating transcription of PKS and TCP genes, suggesting a potential new role of UGT74D1 in regulation of leaf angle in dicot Arabidopsis.

Elicitor Application in Strawberry Results in Long-Term Increase of Plant Resilience Without Yield Loss

For a first step integrating elicitor applications into the current IPM strategy increasing plant resilience against pests, we investigated repeated elicitor treatments in a strawberry everbearer nursery and cropping cycle under glass. During nursery methyl-jasmonate (MeJA), testing induction of defenses with plant bioassays was applied every 3 weeks. Thrips damage and reproduction by spider mites, whitefly and aphids were strongly reduced upon elicitor treatment. Subsequently, we applied MeJA every 3 weeks or based on scouting pests during a whole cropping cycle. Thrips leaf bioassays and LC-MS leaf metabolomics were applied to investigate the induction of defenses. Leaf damage by thrips was lower for both MeJA application schemes compared to the control except for the last weeks. While elicitor treatments after scouting also reduced damage, its effect did not last. Thrips damage decreased from vegetative to mature plants during the cropping cycle. At the end of the nursery phase, plants in the elicitor treatment were smaller. Surprisingly, growth during production was not affected by MeJA application, as were fruit yield and quality. LC-MS leaf metabolomics showed strong induction of vegetative plants decreasing during the maturation of plants toward the end of cultivation. Concurrently, no increase in the JA-inducible marker PPO was observed when measured toward the end of cultivation. Mostly flavonoid and phenolic glycosides known as plant defense compounds were induced upon MeJA application. While induced defense decreased with the maturation of plants, constitutive defense increased as measured in the leaf metabolome of control plants. Our data propose that young, relatively small plant stages lack constitutive defense necessitating an active JA defense response. As plants, mature constitutive defense metabolites seem to accumulate, providing a higher level of basal resistance. Our results have important implications for but are not limited to strawberry cultivation. We demonstrated that repeated elicitor application could be deployed as part of an integrated approach for sustainable crop protection by vertical integration with other management tactics and horizontal integration to control multiple pests concurrently. This approach forms a promising potential for long-term crop protection in greenhouses.

Rice Glycosyltransferase Gene UGT85E1 Is Involved in Drought Stress Tolerance Through Enhancing Abscisic Acid Response

Drought is one of the most important environmental constraints affecting plant growth and development and ultimately leads to yield loss. Uridine diphosphate (UDP)-dependent glycosyltransferases (UGTs) are believed to play key roles in coping with environmental stresses. In rice, it is estimated that there are more than 200 UGT genes. However, most of them have not been identified as their physiological significance. In this study, we reported the characterization of a putative glycosyltransferase gene UGT85E1 in rice. UGT85E1 gene is significantly upregulated by drought stress and abscisic acid (ABA) treatment. The overexpression of UGT85E1 led to an enhanced tolerance in transgenic rice plants to drought stress, while the ugt85e1 mutants of rice showed a more sensitive phenotype to drought stress. Further studies indicated that UGT85E1 overexpression induced ABA accumulation, stomatal closure, enhanced reactive oxygen species (ROS) scavenging capacity, increased proline and sugar contents, and upregulated expression of stress-related genes under drought stress conditions. Moreover, when UGT85E1 was ectopically overexpressed in Arabidopsis, the transgenic plants showed increased tolerance to drought as well as in rice. Our findings suggest that UGT85E1 plays an important role in mediating plant response to drought and oxidative stresses. This work may provide a promising candidate gene for cultivating drought-tolerant crops both in dicots and monocots.

UGT85A53 promotes flowering via mediating abscisic acid glucosylation and FLC transcription in Camellia sinensis

Uridine diphosphate (UDP)-dependent glycosyltransferases catalyse the glycosylation of small molecules and play important roles in maintaining cell homeostasis and regulating plant development. Glycosyltransferases are widely distributed, but their detailed roles in regulating plant growth and development are largely unknown. In this study, we identified a UDP-glycosyltransferase, UGT85A53, from Camellia sinensis, the expression of which was strongly induced by various abiotic stress factors and its protein product was distributed in both the cytoplasm and nucleus. Ectopic overexpression of CsUGT85A53 in Arabidopsis resulted in an early-flowering phenotype under both long- and short-day conditions. The transcript accumulation of the flowering repressor genes FLC and ABI5, an activator of FLC in ABA-regulated flowering signaling, were both significantly decreased in transgenic Arabidopsis compared with wild-type plants. The decreased expression level of FLC might be associated with an increased level of DNA methylation that was observed in CsUGT85A53-overexpressing (OE) plants. Biochemical analyses showed that CsUGT85A53 could glucosylate ABA to form inactive ABA-glycoside in vitro and in planta. Overexpression of CsUGT85A53 in Arabidopsis resulted in a decreased concentration of free ABA and increased concentration of ABA-glucoside. The early-flowering phenotype in the CsUGT85A53-OE transgenic lines was restored by ABA application. Furthermore, CsUGT85A53-OE plants displayed an ABA-insensitive phenotype with higher germination rates compared with controls in the presence of low concentrations of exogenous ABA. Our findings are the first to identify a UGT in tea plants that catalyses ABA glucosylation and enhance flowering transition as a positive regulator.

A cellulose synthase-derived enzyme catalyses 3-O-glucuronosylation in saponin biosynthesis

Triterpenoid saponins are specialised metabolites distributed widely in the plant kingdom that consist of one or more sugar moieties attached to triterpenoid aglycones. Despite the widely accepted view that glycosylation is catalysed by UDP-dependent glycosyltransferase (UGT), the UGT which catalyses the transfer of the conserved glucuronic acid moiety at the C-3 position of glycyrrhizin and various soyasaponins has not been determined. Here, we report that a cellulose synthase superfamily-derived glycosyltransferase (CSyGT) catalyses 3-O-glucuronosylation of triterpenoid aglycones. Gene co-expression analyses of three legume species (Glycyrrhiza uralensis, Glycine max, and Lotus japonicus) reveal the involvement of CSyGTs in saponin biosynthesis, and we characterise CSyGTs in vivo using Saccharomyces cerevisiae. CSyGT mutants of L. japonicus do not accumulate soyasaponin, but the ectopic expression of endoplasmic reticulum membrane-localised CSyGTs in a L. japonicus mutant background successfully complement soyasaponin biosynthesis. Finally, we produced glycyrrhizin de novo in yeast, paving the way for sustainable production of high-value saponins.

Full-length transcriptome sequencing and modular organization analysis of oleanolic acid- and dammarane-type saponins related gene expression patterns in Panax japonicus

The saponins found in Panax japonicus, a traditional medicinal herb in Asia, exhibit high degrees of structural and functional similarity. In this study, metabolite analysis revealed that oleanolic acid-type and dammarane-type saponins were distributed unevenly in three tissues (rhizome_Y, rhizome_O, and secRoot) of P. japonicus. Single-molecule real-time (SMRT) sequencing and next generation sequencing (NGS) data revealed distinct and tissue-specific transcriptomic patterns relating to the production of these two types of saponins. In the co-expression network and hierarchical clustering analyses, one 3-hydroxy-3-methylglutaryl-CoA reductase (HMGR) and two 1-deoxy-D-xylulose-5-phosphate synthase (DXS) etc. transcripts were found to be key genes associated with the biosynthesis of oleanolic acid and dammarane-type saponins in P. japonicus, respectively. In addition, cytochrome p450 (CYP) and UDP-glucuronosyltransferase (UGT) family proteins that serve as regulators of saponin biosynthesis-related genes were also found to exhibit tissue-specific expression patterns. Together these results offer a comprehensive metabolomic and transcriptomic overview of P. japonicus.

Selective profiling of steviol-catalyzing UDP-glycosyltransferases with a metabolically synthesized probe

Selective profiling of steviol-catalyzing UDP-glycosyltransferases in plants was accomplished with a probe metabolically synthesized from two substrate-derived components comprising an alkynylated sugar receptor (steviol) module and a diazirine-modified sugar donor (UDP-glucose) module, thereby illustrating a facile approach for harnessing biosynthetic enzymes of natural glycosides in plants for synthetic biology.

Regioselective Hydroxylation of Naringin Dihydrochalcone to Produce Neoeriocitrin Dihydrochalcone by CYP102A1 (BM3) Mutants

Naringin dihydrochalcone (DC) is originally derived from the flavonoid naringin, which occurs naturally in citrus fruits, especially in grapefruit. It is used as an artificial sweetener with a strong antioxidant activity with potential applications in food and pharmaceutical fields. At present, enzymatic and chemical methods to make products of naringin DC by hydroxylation reactions have not been developed. Here, an enzymatic strategy for the efficient synthesis of potentially valuable products from naringin DC, a glycoside of phloretin, was developed using Bacillus megaterium CYP102A1 monooxygenase. The major product was identified to be neoeriocitrin DC by NMR and LC-MS analyses. Sixty-seven mutants of CYP102A1 were tested for hydroxylation of naringin DC to produce neoeriocitrin DC. Six mutants with high activity were selected to determine the kinetic parameters and total turnover numbers (TTNs). The kcat value of the most active mutant was 11 min−1 and its TTN was 315. The productivity of neoeriocitrin DC production increased up to 1.1 mM h−1, which corresponds to 0.65 g L−1 h−1. In this study, we achieved a regioselective hydroxylation of naringin DC to produce neoeriocitrin DC.

An Ambidextrous Polyphenol Glycosyltransferase PaGT2 from Phytolacca americana

The glycosylation of small hydrophobic compounds is catalyzed by uridine diphosphate glycosyltransferases (UGTs). Because glycosylation is an invaluable tool for improving the stability and water solubility of hydrophobic compounds, UGTs have attracted attention for their application in the food, cosmetics, and pharmaceutical industries. However, the ability of UGTs to accept and glycosylate a wide range of substrates is not clearly understood due to the existence of a large number of UGTs. PaGT2, a UGT from Phytolacca americana, can regioselectively glycosylate piceatannol but has low activity toward other stilbenoids. To elucidate the substrate specificity and catalytic mechanism, we determined the crystal structures of PaGT2 with and without substrates and performed molecular docking studies. The structures have revealed key residues involved in substrate recognition and suggest the presence of a nonconserved catalytic residue (His81) in addition to the highly conserved catalytic histidine in UGTs (His18). The role of the identified residues in substrate recognition and catalysis is elucidated with the mutational assay. Additionally, the structure-guided mutation of Cys142 to other residues, Ala, Phe, and Gln, allows PaGT2 to glycosylate resveratrol with high regioselectivity, which is negligibly glycosylated by the wild-type enzyme. These results provide a basis for tailoring an efficient glycosyltransferase.

Apple SERRATE negatively mediates drought resistance by regulating MdMYB88 and MdMYB124 and microRNA biogenesis

The function of serrate (SE) in miRNA biogenesis in Arabidopsis is well elucidated, whereas its role in plant drought resistance is largely unknown. In this study, we report that MdSE acts as a negative regulator of apple (Malus × domestica) drought resistance by regulating the expression levels of MdMYB88 and MdMYB124 and miRNAs, including mdm-miR156, mdm-miR166, mdm-miR172, mdm-miR319, and mdm-miR399. MdSE interacts with MdMYB88 and MdMYB124, two positive regulators of apple drought resistance. MdSE decreases the transcript and protein levels of MdMYB88 and MdMYB124, which directly regulate the expression of MdNCED3, a key enzyme in abscisic acid (ABA) biosynthesis. Furthermore, MdSE is enriched in the same region of the MdNECD3 promoter where MdMYB88/MdMYB124 binds. Consistently, MdSE RNAi transgenic plants are more sensitive to ABA-induced stomatal closure, whereas MdSE OE plants are less sensitive. In addition, under drought stress, MdSE is responsible for the biogenesis of mdm-miR399, a negative regulator of drought resistance, and negatively regulates miRNAs, including mdm-miR156, mdm-miR166, mdm-miR172, and mdm-miR319, which are positive regulators of drought resistance. Taken together, by revealing the negative role of MdSE, our results broaden our understanding of the apple drought response and provide a candidate gene for apple drought improvement through molecular breeding.

Genome-Wide Analysis of Serine Carboxypeptidase-Like Acyltransferase Gene Family for Evolution and Characterization of Enzymes Involved in the Biosynthesis of Galloylated Catechins in the Tea Plant (Camellia sinensis)

Tea (Camellia sinensis L.) leaves synthesize and concentrate a vast array of galloylated catechins (e.g., EGCG and ECG) and non-galloylated catechins (e.g., EGC, catechin, and epicatechin), together constituting 8%-24% of the dry leaf mass. Galloylated catechins account for a major portion of soluble catechins in tea leaves (up to 75%) and make a major contribution to the astringency and bitter taste of the green tea, and their pharmacological activity for human health. However, the catechin galloylation mechanism in tea plants is largely unknown at molecular levels. Previous studies indicated that glucosyltransferases and serine carboxypeptidase-like acyltransferases (SCPL) might be involved in the process. However, details about the roles of SCPLs in the biosynthesis of galloylated catechins remain to be elucidated. Here, we performed the genome-wide identification of SCPL genes in the tea plant genome. Several SCPLs were grouped into clade IA, which encompasses previously characterized SCPL-IA enzymes with an acylation function. Twenty-eight tea genes in this clade were differentially expressed in young leaves and vegetative buds. We characterized three SCPL-IA enzymes (CsSCPL11-IA, CsSCPL13-IA, CsSCPL14-IA) with galloylation activity toward epicatechins using recombinant enzymes. Not only the expression levels of these SCPLIA genes coincide with the accumulation of galloylated catechins in tea plants, but their recombinant enzymes also displayed β-glucogallin:catechin galloyl acyltransferase activity. These findings provide the first insights into the identities of genes encoding glucogallin:catechin galloyl acyltransferases with an active role in the biosynthesis of galloylated catechins in tea plants.

Glycosyltransferase GT1 family: Phylogenetic distribution, substrates coverage, and representative structural features

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The phylogenetic distribution of GT1 family enzymes showed domain-dependent pattern.

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The domain-dependent characterized GTs showed distinct substrates spectrum.

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Two regions that discriminate the GT1 enzymes from different domains were identified.

Glycosyltransferases (GTs) are responsible for transferring glycosyl moieties from activated sugar donors to certain acceptors, among which the GT1 family enzymes have been known for their outstanding glycosylation capacities toward diverse natural products, such as glycolipids, flavonoids and macrolides etc. However, there still lacks a systematic collation of this important family members. In this minireview, all the GT1 family sequences were phylogenetically analyzed, and the grouping of GT1 proteins exhibited a taxonomic life domain-dependent pattern, revealing many untapped clades of GTs. The further phylogenetic analysis of the characterized GTs facilitated the classification of substrates coverage of GT1 family enzymes from different life domains, whereby the GTs from bacteria can tolerate a wider spectrum of chemical skeletons as substrates, showing higher promiscuity than those from other domains. Furthermore, the sequence sizes of GTs from different domains were compared to understand their different substrates selectivity. Based on the multiple sequence alignments of 28 representative GT1 enzymes with crystal structures, two critical regions located in the N-terminal of GTs were identified, which were most variable among sequences from different taxonomic domains and essential for substrates binding and/or catalysis. The key roles of these two regions were validated by enumerating the influential residues that interacted with substrates in the representative structures from bacteria and plants. The atlas for GT1 family in terms of phylogeny, substrates selectivity, sequence length, and critical motifs provides the clues for the exploration of unknown GT1s and rational engineering of known enzymes, synthesizing novel promising glycoconjugates for pharmaceutical application.

Exploiting Citrus aurantium seeds and their secondary metabolites in the management of Alzheimer disease

Fruit by-products are considered nature’s golden gift for human health and a good starting point to discover new drugs depending on the fact that they contain millions of bio-active compounds that are responsible for therapeutic activities. In this context, the main goal of this study is to recycle Citrus aurantium (C. aurantium) seeds to produce pharmaceutical molecules to be used in the prevention of the progressive neurological damage associated with Alzheimer disease (AD). Donepezil (0.75 mg/kg), hesperidin (125 and 250 mg/kg) and limonoids (50 and 100 mg/kg) were used for treatment of rats for 2 weeks prior to concomitant administration of AlCl₃ for three successive weeks. Protection against cognitive deterioration was observed among study group with insignificant difference from normal control group and significant difference from positive control group in the Y-Maze test. On the other hand, treatment with both doses of hesperidin (125 and 250 mg/kg) and high dose of limonoids only (100 mg/kg) produced improvement in psychological state, observed by significant increase in ambulation frequency in comparison to positive control group, however it was not as frequent as normal group, as it was significantly less than normal group in the open field test. Regarding acetylcholine esterase (AChE) and beta-amyloid (β amyloid) levels, the effect of limonoids low dose was the best as it didn’t have a significant effect when compared to normal control, also hesperidin in both doses showed insignificant effects on β amyloid levels when compared to normal control group. Our results encourage the use of C. aurantium seeds which are wasted in huge amounts, as Alzheimer prophylactic food additives.

UDP-glycosyltransferases contribute to spirotetramat resistance in Aphis gossypii Glover

Uridine diphosphate (UDP)-glycosyltransferases (UGTs) catalyze the conjugation of small lipophilic endogenous and exogenous compounds with sugars to produce water-soluble glycosides, playing an important role in insect endobiotic regulation and xenobiotic detoxification. In this study, two UGT-inhibitors, sulfinpyrazone and 5-nitrouracil, significantly increased spirotetramat toxicity against third instar nymphs of resistant Aphis gossypii, whereas there were no synergistic effects in apterous adult aphids, suggesting UGT involvement in spirotetramat resistance in cotton aphids. Furthermore, the UHPLC-MS/MS was employed to determine the content of spirotetramat and its four metabolites (S-enol, S-glu, S-mono, S-keto) in the honeydew of resistant cotton aphids under spirotetramat treatment. No residual spirotetramat was detected in the honeydew, while its four metabolites were detected at a S-enol: S-glu: S-mono: S-keto ratio of 69.30: 6.54: 1.44: 1.00. Therefore, glycoxidation plays a major role in spirotetramat inactivation and excretion in resistant aphids. Compared with the susceptible strain, the transcriptional levels of UGT344M2 were significantly upregulated in nymphs and adults of the resistant strain. RNA interference of UGT344M2 dramatically increased spirotetramat toxicity in nymphs, but no such effect were found in the resistant adult aphids. Overall, UGT-mediated glycoxidation were found to be involved in spirotetramat resistance. The suppression of UGT344M2 significantly increased the sensitivity of resistant nymphs to spirotetramat, suggesting that UGT344M2 upregulation might be associated with spirotetramat detoxification. This study provides an overview of the involvement of metabolic factors, UGTs, in the development of spirotetramat resistance.

Crown-ether-mediated crystal structures of the glycosyltransferase PaGT3 from Phytolacca americana

Uridine diphosphate glycosyltransferases (UGTs) are ubiquitous enzymes that are involved in the glycosylation of small molecules. As glycosylation improves the water solubility and stability of hydrophobic compounds, interest in the use of UGTs for the synthesis of glycosides of poorly soluble compounds is increasing. While sugar-donor recognition in UGTs is conserved with the presence of a plant secondary product glycosyltransferase (PSPG) motif, the basis of the recognition of the sugar acceptor and the regioselectivity of the products is poorly understood owing to low sequence identity around the acceptor-binding region. PaGT3, a glycosyltransferase from the plant Phytolacca americana, can glycosylate a range of acceptors. To illustrate the structure-function relationship of PaGT3, its crystal structure was determined. The sugar-donor and sugar-acceptor binding pockets in PaGT3 were recognized by comparison of its structure with those of other UGTs. The key feature of PaGT3 was the presence of longer loop regions around the hydrophobic acceptor-binding pocket, which resulted in a flexible and wider acceptor binding pocket. In this study, PaGT3 crystals were grown by co-crystallization with 18-crown-6 ether or 15-crown-5 ether. The crown-ether molecule in the asymmetric unit was observed to form a complex with a metal ion, which was coordinated on two sides by the main-chain O atoms of Glu238 from two molecules of the protein. The crown ether-metal complex resembles a molecular glue that sticks two molecules of PaGT3 together to enhance crystal growth. Thus, this result provides an insight into the substrate-recognition strategy in PaGT3 for the study of glycosyltransferases. Additionally, it is shown that crown ether-metal ion complexes can be used as a molecular glue for the crystallization of proteins.

De novo transcriptome analysis unravels tissue-specific expression of candidate genes involved in major secondary metabolite biosynthetic pathways of Plumbago zeylanica: implication for pharmacological potential

KEY MESSAGE

The present study provides comparative transcriptome analysis, besides identifying functional secondary metabolite genes of Plumbago zeylanica with pharmacological potential for future functional genomics, and metabolomic engineering of secondary metabolites from this plant towards diversified biomedical applications.

ABSTRACT

Plumbago zeylanica is a widely used medicinal plant of the traditional Indian system of medicine with wide pharmacological potential to treat several disorders. The present study aimed to carry out comparative transcriptome analysis in leaf and root tissue of P. zeylanica using Illumina paired end sequencing to identify tissue-specific functional genes involved in the biosynthesis of secondary metabolites, contributing to its therapeutic efficacy. De novo sequencing assembly resulted in the identification of 62,321 "Unigenes" transcripts with an average size of 1325 bp. Functional annotation using BLAST2GO resulted in the identification of 50,301 annotated transcripts (80.71%) and GO assigned to 18,814 transcripts. KEGG pathway annotation of the "Unigenes" revealed that 2465 transcripts could be assigned to 242 KEGG pathway maps wherein the number of transcripts involved in secondary metabolism was distinct in root and leaf transcriptome. Among the secondary metabolite biosynthesis pathways, the cluster of "Unigenes" encoding enzymes of 'Phenylpropanoid biosynthesis pathway' represents the largest group (84 transcripts) followed by 'Terpenoid Backbone biosynthesis' (48 transcripts). The transcript levels of the candidate unigenes encoding key enzymes of phenylpropanoid (PAL, TAL) and flavanoid biosynthesis (CHS, ANS, FLS) pathways were up-regulated in root, while the expression levels of candidate "Unigenes" transcript for monoterpenoid (DXS, ISPF), diterpenoid biosynthesis (SPS, SDS) and indole alkaloid pathways (STR) were significantly higher in leaf of P. zeylanica. Interestingly, validation of differential gene expression profile by qRT-PCR also confirmed that candidate "Unigenes" enzymes of phenylpropanoid and flavonoid biosynthesis were highly expressed in the root, while the key regulatory enzymes of terpenoid and indole alkaloid compounds were up-regulated in the leaf, suggesting that (differences in) the levels of these functional genes could be attributed to the (differential) pharmacological activity (between root and leaf) in tissues of P. zeylanica.

Steviol glycosides profile in Stevia rebaudiana Bertoni hairy roots cultured under oxidative stress-inducing conditions

The ability to synthesize particular steviol glycosides (SvGls) was studied in Stevia rebaudiana Bertoni hairy roots (HR) grown in the light or in the dark under the influence of different osmotic active compounds. Manipulation of culture conditions led to changes in the morphology and growth rate of HR, as well as to an increase in oxidative stress manifested as an enhancement in endogenous hydrogen peroxide concentration in the cultured samples. The highest level of H₂O₂ was noted in HR cultured under light or in the medium with the highest osmotic potential. This correlated with the highest increase in the expression level of ent-kaurenoic acid hydroxylase, responsible for the redirection of metabolic route to SvGls biosynthesis pathway. An analysis of transcriptional activity of some UDPglucosyltransferase (UGT85c2, UGT74g1, UGT76g1) revealed that all of them were upregulated due to the manipulation of culture conditions. However, the level of their upregulation depended on the type of stress factor used in our experiment. Analysis of SvGls content revealed that HR grown under all applied conditions were able to synthesize and accumulate several SvGls but their concentration differed between the samples across the different conditions. The level of rebaudioside A concentration exceeded the content of stevioside in HR in all tested conditions. Concomitantly, the presence of some minor SvGls, such as steviolbioside and rebaudioside F, was confirmed only in HR cultured in the lowest osmotic potential of the medium while rebaudioside D was also detected in the samples cultured in the media supplemented with NaCl or PEG.Key Points● Several steviol glycosides are synthesized in hairy roots of S. rebaudiana.● Light or osmotic factors cause enhancement in oxidative stress level in hairy roots.● It correlates with a significant increase in the level of KAH expression.● UGTs expression and steviol glycosides content depends on culture conditions.

Phyto-derived Products as Matrix Metalloproteinases Inhibitors in Cardiovascular Diseases

Matrix metalloproteinases (MMPs) are enzymes that present a metallic element in their structure. These enzymes are ubiquitously distributed and function as extracellular matrix (ECM) remodelers. MMPs play a broad role in cardiovascular biology regulating processes such as cell adhesion and function, cellular communication and differentiation, integration of mechanical force and force transmission, tissue remodeling, modulation of damaged-tissue structural integrity, cellular survival or apoptosis and regulation of inflammation-related cytokines and growth factors. MMPs inhibition and downregulation are correlated with minimization of cardiac damage, i.e., Chinese herbal medicine has shown to stabilize abdominal aorta aneurysm due to its antiinflammatory, antioxidant and MMP-2 and 9 inhibitory properties. Thus phyto-derived products rise as promising sources for novel therapies focusing on MMPs inhibition and downregulation to treat or prevent cardiovascular disorders.

Glycosyltransferase OsUGT90A1 helps protect the plasma membrane during chilling stress in rice

Due to its subtropical origins, rice (Oryza sativa) is sensitive to low-temperature stress. In this study, we identify LOC_Os04g24110, annotated to encode the UDP-glycosyltransferase enzyme UGT90A1, as a gene associated with the low-temperature seedling survivability (LTSS) quantitative trait locus qLTSS4-1. Differences between haplotypes in the control region of OsUGT90A1 correlate with chilling tolerance phenotypes, and reflect differential expression between tolerant and sensitive accessions rather than differences in protein sequences. Expression of OsUGT90A1 is initially enhanced by low temperature, and its overexpression helps to maintain membrane integrity during cold stress and promotes leaf growth during stress recovery, which are correlated with reduced levels of reactive oxygen species due to increased activities of antioxidant enzymes. In addition, overexpression of OsUGT90A1 in Arabidopsis improves freezing survival and tolerance to salt stress, again correlated with enhanced activities of antioxidant enzymes. Overexpression of OsUGT90A1 in rice decreases root lengths in 3-week-old seedlings while gene-knockout increases the length, indicating that its differential expression may affect phytohormone activities. We conclude that higher OsUGT90A1 expression in chilling-tolerant accessions helps to maintain cell membrane integrity as an abiotic stress-tolerance mechanism that prepares plants for the resumption of growth and development during subsequent stress recovery.

Genetic Studies on the Inheritance of Storage-Induced Cooking Time in Cowpeas [Vigna unguiculata (L.) Walp]

Cowpeas provide food and income for many small-holder farmers in Africa. Cowpea grains contain substantial quantities of protein, carbohydrates, vitamins, and fiber. In areas where subsistence farming is practiced, cowpea's protein is cheaper than that obtained from other sources such as fish, meat, poultry or dairy products and combines well with cereal grains in diets. However, long-cooking times, typical of many grain legumes, is a major limitation to the utilization of cowpeas especially among the low-income and growing middle-income population of Africa. Long periods of cooking cowpeas lead to loss of nutrients, loss of useful time and increased greenhouse gas emission through increased burning of firewood. Fast-cooking cowpeas has the potential to deliver highly nutritious food to the hungry within shorter periods, encourage less use of firewood, improve gender equity, increase the consumption of cowpeas, trigger an increase in demand for cowpeas and thus incentivize cowpea production by smallholder farmers in Sub-Saharan Africa. In this study, the inheritance of storage-induced cooking time in cowpeas was investigated. Two sets of bi-parental crosses were conducted involving three cowpea genotypes: CRI-11(1)-1, C9P(B) and TVu7687. Generation means from six generations were used to determine the phenotypic and genotypic variances and coefficients of variation. Broad and narrow sense heritabilities and genetic advance percentage of mean were estimated. Generation mean analysis showed that additive, dominant, additive-additive, additive-dominant, and dominant-dominant gene actions were significant (p < 0.001). Fast-cooking trait was dominant over the long-cooking trait. Broad sense heritability for crosses C9P(B) × CRI-11(1)-1 and TVu7687 × CRI-11(1)-1 were 0.94 and 0.99 respectively while narrow sense heritabilities were 0.84 and 0.88 respectively. Genetic advances were 27.09 and 40.40 respectively. High narrow-sense heritabilities and moderate genetic advance for the fast-cooking trait indicated the presence of additive genes in the trait and the possibility of introgressing the trait into farmer-preferred varieties using conventional selection methods. However, due to significant epistatic gene effects observed, effective selection for fast-cooking trait would be appropriate at advanced generations.

Coimmobilization and colocalization of a glycosyltransferase and a sucrose synthase greatly improves the recycling of UDP-glucose: Glycosylation of resveratrol 3-O-β-D-glucoside

Glycosylation is one of the most efficient biocompatible methodologies to enhance the water solubility of natural products, and therefore their bioavailability. The excellent regio- and stereoselectivity of nucleotide sugar-dependent glycosyltransferases enables single-step glycosylations at specific positions of a broad variety of acceptor molecules without the requirement of protection/deprotection steps. However, the need for stoichiometric quantities of high-cost substrates, UDP-sugars, is a limiting factor for its use at an industrial scale. To overcome this challenge, here we report tailor-made coimmobilization and colocalization procedures to assemble a bi-enzymatic cascade composed of a glycosyltransferase and a sucrose synthase for the regioselective 5-O-β-D-glycosylation of piceid with in situ cofactor regeneration. Coimmobilization and colocalization of enzymes was achieved by performing slow immobilization of both enzymes inside the porous support. The colocalization of both enzymes within the porous structure of a solid support promoted an increase in the overall stability of the bi-enzymatic system and improved 50-fold the efficiency of piceid glycosylation compared with the non-colocalized biocatalyst. Finally, piceid conversion to resveratrol 3,5-diglucoside was over 90% after 6 cycles using the optimal biocatalyst and was reused in up to 10 batch reaction cycles accumulating a TTN of 91.7 for the UDP recycling.

Sesquiterpene glucosylation mediated by glucosyltransferase UGT91Q2 is involved in the modulation of cold stress tolerance in tea plants

Plants produce and emit terpenes, including sesquiterpenes, during growth and development, which serve different functions in plants. The sesquiterpene nerolidol has health-promoting properties and adds a floral scent to plants. However, the glycosylation mechanism of nerolidol and its biological roles in plants remained unknown. Sesquiterpene UDP-glucosyltransferases were selected by using metabolites-genes correlation analysis, and its roles in response to cold stress were studied. We discovered the first plant UGT (UGT91Q2) in tea plant, whose expression is strongly induced by cold stress and which specifically catalyzes the glucosylation of nerolidol. The accumulation of nerolidol glucoside was consistent with the expression level of UGT91Q2 in response to cold stress, as well as in different tea cultivars. The reactive oxygen species (ROS) scavenging capacity of nerolidol glucoside was significantly higher than that of free nerolidol. Down-regulation of UGT91Q2 resulted in reduced accumulation of nerolidol glucoside, ROS scavenging capacity and tea plant cold tolerance. Tea plants absorbed airborne nerolidol and converted it to its glucoside, subsequently enhancing tea plant cold stress tolerance. Nerolidol plays a role in response to cold stress as well as in triggering plant-plant communication in response to cold stress. Our findings reveal previously unidentified roles of volatiles in response to abiotic stress in plants.

Functional analysis of UGT201D3 associated with abamectin resistance in Tetranychus cinnabarinus (Boisduval)

Uridine diphosphate (UDP)-glycosyltransferases (UGTs) are widely distributed within living organisms and share roles in biotransformation of various lipophilic endo- and xenobiotics with activated UDP sugars. In this study, it was found that the activity of UGTs in abamectin-resistant (AbR) strain was significantly higher (2.35-fold) than that in susceptible strain (SS) of Tetranychus cinnabarinus. Further analysis showed that 5-nitrouracil, the inhibitor of UGTs, could enhance the lethal effect of abamectin on mites. From the previous microarray results, we found an UGT gene (UGT201D3) overexpressed in AbR strain. Quantitative PCR analysis showed that UGT201D3 was highly expressed and more inducible with abamectin exposure in the AbR strain. After silencing the transcription of UGT201D3, the activity of UGTs was decreased and the susceptibility to abamectin was increased in AbR strain whereas it was not in SS. Furthermore, UGT201D3 gene was then successfully expressed in Escherichia coli. The recombinant UGT201D3 exhibited α-naphthol activity (2.81 ± 0.43 nmol/mg protein/min), and the enzyme activity could be inhibited by abamectin (inhibitory concentration at 50%: 57.50 ± 3.54 μmol/L). High-performance liquid chromatography analysis demonstrated that the recombinant UGT201D3 could effectively deplete abamectin (15.77% ± 3.72%) incubating with 150 μg protein for 6 h. These results provided direct evidence that UGT201D3 was involved in abamectin resistance in T. cinnabarinus.

Comparative Analysis of High-Throughput Assays of Family-1 Plant Glycosyltransferases

The ability of glycosyltransferases (GTs) to reduce volatility, increase solubility, and thus alter the bioavailability of small molecules through glycosylation has attracted immense attention in pharmaceutical, nutraceutical, and cosmeceutical industries. The lack of GTs known and the scarcity of high-throughput (HTP) available methods, hinders the extrapolation of further novel applications. In this study, the applicability of new GT-assays suitable for HTP screening was tested and compared with regard to harmlessness, robustness, cost-effectiveness and reproducibility. The UDP-Glo GT-assay, Phosphate GT Activity assay, pH-sensitive GT-assay, and UDP²-TR-FRET assay were applied and tailored to plant UDP GTs (UGTs). Vitis vinifera (UGT72B27) GT was subjected to glycosylation reaction with various phenolics. Substrate screening and kinetic parameters were evaluated. The pH-sensitive assay and the UDP²-TR-FRET assay were incomparable and unsuitable for HTP plant GT-1 family UGT screening. Furthermore, the UDP-Glo GT-assay and the Phosphate GT Activity assay yielded closely similar and reproducible K_M, v_max, and k_cat values. Therefore, with the easy experimental set-up and rapid readout, the two assays are suitable for HTP screening and quantitative kinetic analysis of plant UGTs. This research sheds light on new and emerging HTP assays, which will allow for analysis of novel family-1 plant GTs and will uncover further applications.

Reconstruction of the Evolutionary Histories of UGT Gene Superfamily in Legumes Clarifies the Functional Divergence of Duplicates in Specialized Metabolism

Plant uridine 5'-diphosphate glycosyltransferases (UGTs) influence the physiochemical properties of several classes of specialized metabolites including triterpenoids via glycosylation. To uncover the evolutionary past of UGTs of soyasaponins (a group of beneficial triterpene glycosides widespread among Leguminosae), the UGT gene superfamily in Medicago truncatula, Glycine max, Phaseolus vulgaris, Lotus japonicus, and Trifolium pratense genomes were systematically mined. A total of 834 nonredundant UGTs were identified and categorized into 98 putative orthologous loci (POLs) using tree-based and graph-based methods. Major key findings in this study were of, (i) 17 POLs represent potential catalysts for triterpene glycosylation in legumes, (ii) UGTs responsible for the addition of second (UGT73P2: galactosyltransferase and UGT73P10: arabinosyltransferase) and third (UGT91H4: rhamnosyltransferase and UGT91H9: glucosyltransferase) sugars of the C-3 sugar chain of soyasaponins were resulted from duplication events occurred before and after the hologalegina-millettoid split, respectively, and followed neofunctionalization in species-/ lineage-specific manner, and (iii) UGTs responsible for the C-22-O glycosylation of group A (arabinosyltransferase) and DDMP saponins (DDMPtransferase) and the second sugar of C-22 sugar chain of group A saponins (UGT73F2: glucosyltransferase) may all share a common ancestor. Our findings showed a way to trace the evolutionary history of UGTs involved in specialized metabolism.

In Vitro and In Vivo Effects of Flavonoids on Peripheral Neuropathic Pain

Neuropathic pain is a common symptom and is associated with an impaired quality of life. It is caused by the lesion or disease of the somatosensory system. Neuropathic pain syndromes can be subdivided into two categories: central and peripheral neuropathic pain. The present review highlights the peripheral neuropathic models, including spared nerve injury, spinal nerve ligation, partial sciatic nerve injury, diabetes-induced neuropathy, chemotherapy-induced neuropathy, chronic constriction injury, and related conditions. The drugs which are currently used to attenuate peripheral neuropathy, such as antidepressants, anticonvulsants, baclofen, and clonidine, are associated with adverse side effects. These negative side effects necessitate the investigation of alternative therapeutics for treating neuropathic pain conditions. Flavonoids have been reported to alleviate neuropathic pain in murine models. The present review elucidates that several flavonoids attenuate different peripheral neuropathic pain conditions at behavioral, electrophysiological, biochemical and molecular biological levels in different murine models. Therefore, the flavonoids hold future promise and can be effectively used in treating or mitigating peripheral neuropathic conditions. Thus, future studies should focus on the structure-activity relationships among different categories of flavonoids and develop therapeutic products that enhance their antineuropathic effects.

UGT74AF3 enzymes specifically catalyze the glucosylation of 4-hydroxy-2,5-dimethylfuran-3(2H)-one, an important volatile compound in Camellia sinensis

4-Hydroxy-2,5-dimethylfuran-3(2H)-one (HDMF) is an important odorant in some fruits, and is proposed to play a crucial role in the caramel-like notes of some teas. However, its biosynthesis and metabolism in tea plants are still unknown. Here, HDMF glucoside was unambiguously identified as a native metabolite in tea plants. A novel glucosyltransferase UGT74AF3a and its allelic protein UGT74AF3b specifically catalyzed the glucosylation of HDMF and the commercially important structural homologues 2 (or 5)-ethyl-4-hydroxy-5 (or 2)-methylfuran-3(2H)-one (EHMF) and 4-hydroxy-5-methylfuran-3(2H)-one (HMF) to their corresponding β-D-glucosides. Site-directed mutagenesis of UGT74AF3b to introduce a single A456V mutation resulted in improved HDMF and EHMF glucosylation activity and affected the sugar donor preference compared with that of the wild-type control enzyme. The accumulation of HDMF glucoside was consistent with the transcript levels of UGT74AF3 in different tea cultivars. In addition, transient UGT74AF3a overexpression in tobacco significantly increased the HDMF glucoside contents, and downregulation of UGT74AF3 transcripts in tea leaves significantly reduced the concentration of HDMF glucoside compared with the levels in the controls. The identification of HDMF glucoside in the tea plant and the discovery of a novel-specific UDP-glucose:HDMF glucosyltransferase in tea plants provide the foundation for improvement of tea flavor and the biotechnological production of HDMF glucoside.

Investigating the Catalytic Activity of Glycosyltransferase on Quercetin from Tripterygium wilfordii

Flavonoid glycosides have shown many pharmacological activities in clinical studies. However, the main way to obtain flavonoid glycosides is to extract and separate them from plants, which wastes both time and resources. Here, we identified the O-glycosyltransferase (UGTs) TwUGT3 from Tripterygium wilfordii and analyzed its bioinformatics. First, the enzyme was found to utilize phloretin and uridine diphosphate glucose (UDPG) as substrates to produce an acid-tolerant glucoside. Then, it also can use quercetin and UDPG as substrates to produce the corresponding O-glucoside. In addition, we further explored the substrate specificity of TwUGT3, which suggested that it also accepts luteolin, pinocembrin, and genistein to produce the corresponding O-glucosides. Subsequently, the optimum pH, reaction time, reaction temperature, and enzymatic kinetic parameters of TwUGT3 were determined.

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.

An Arabidopsis Cytokinin-Modifying Glycosyltransferase UGT76C2 Improves Drought and Salt Tolerance in Rice

Drought and salt stresses are common environmental threats that negatively affect rice development and yield. Here we report that the overexpression of AtUGT76C2, a cytokinin glycosyltransferase, in rice modulates cytokinin homeostasis and confers the plants an eminent property in drought and salt tolerance. The transgenic plants exhibit sensitivity to salt and drought stress as well as abscisic acid during the germination stage and the postgermination stage while showing enhanced tolerance to drought and salinity at the young seedling stage and the mature stage. The overexpression of UGT76C2 decreases the endogenous cytokinin level and enhances root growth, which greatly contributes to stress adaptation. In addition, the transgenic plants also show enhanced ROS scavenging activity, reduced ion leakage under salt stress, smaller stomatal opening, and more proline and soluble sugar accumulation, which demonstrate that UGT76C2 acts as an important player in abiotic stress response in rice. To explore the molecular mechanism of UGT76C2 in response to stress adaptation, the expressions of eight stress-responsive genes including OsSOS1, OsPIP2.1, OsDREB2A, OsCOIN, OsABF2, OsRAB16, OsP5CR, and OsP5CS1 were detected, which showed notable upregulation in UGT76C2 overexpression plants under salt and drought stresses. Our results reveal that the ectopic expression of AtUGT76C2 confers the transgenic rice many traits in improving drought and salt stress tolerance in both developmental and physiological levels. It is believed that AtUGT76C2 could be a promising candidate gene for cultivating saline- and drought-tolerant rice.

The Actual and Potential Aroma of Winemaking Grapes

This review intends to rationalize the knowledge related to the aroma of grapes and to the aroma of wine with specific origin in molecules formed in grapes. The actual flavor of grapes is formed by the few free aroma molecules already found in the pulp and in the skin, plus by those aroma molecules quickly formed by enzymatic/catalytic reactions. The review covers key aroma components of aromatic grapes, raisins and raisinized grapes, and the aroma components responsible from green and vegetal notes. This knowledge is used to explain the flavor properties of neutral grapes. The aroma potential of grape is the consequence of five different systems/pools of specific aroma precursors that during fermentation and/or aging, release wine varietal aroma. In total, 27 relevant wine aroma compounds can be considered that proceed from grape specific precursors. Some of them are immediately formed during fermentation, while some others require long aging time to accumulate. Precursors are glycosides, glutathionyl and cysteinyl conjugates, and other non-volatile molecules.

Biosynthesis of the anti-diabetic metabolite montbretin A: glucosylation of the central intermediate mini-MbA

Type 2 diabetes (T2D) affects over 320 million people worldwide. Healthy lifestyles, improved drugs and effective nutraceuticals are different components of a response against the growing T2D epidemic. The specialized metabolite montbretin A (MbA) is being developed for treatment of T2D and obesity due to its unique pharmacological activity as a highly effective and selective inhibitor of the human pancreatic α-amylase. MbA is an acylated flavonol glycoside found in small amounts in montbretia (Crocosmia × crocosmiiflora) corms. MbA cannot be obtained in sufficient quantities for drug development from its natural source or by chemical synthesis. To overcome these limitations through metabolic engineering, we are investigating the genes and enzymes of MbA biosynthesis. We previously reported the first three steps of MbA biosynthesis from myricetin to myricetin 3-O-(6'-O-caffeoyl)-glucosyl rhamnoside (mini-MbA). Here, we describe the sequence of reactions from mini-MbA to MbA, and the discovery and characterization of the gene and enzyme responsible for the glucosylation of mini-MbA. The UDP-dependent glucosyltransferase CcUGT3 (UGT703E1) catalyzes the 1,2-glucosylation of mini-MbA to produce myricetin 3-O-(glucosyl-6'-O-caffeoyl)-glucosyl rhamnoside. Co-expression of CcUGT3 with genes for myricetin and mini-MbA biosynthesis in Nicotiana benthamiana validated its biological function and expanded the set of genes available for metabolic engineering of MbA.

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.

Identification and Characterization of Apigenin 6-C-Glucosyltransferase Involved in Biosynthesis of Isosaponarin in Wasabi (Eutrema japonicum)

Wasabi (Eutrema japonicum) is a perennial plant native to Japan that is used as a spice because it contains isothiocyanates. It also contains an isosaponarin, 4'-O-glucosyl-6-C-glucosyl apigenin, in its leaves, which has received increasing attention in recent years for its bioactivity, such as its promotion of type-I collagen production. However, its biosynthetic enzymes have not been clarified. In this study, we partially purified a C-glucosyltransferase (CGT) involved in isosaponarin biosynthesis from wasabi leaves and identified the gene coding for it (WjGT1). The encoded protein was similar to UGT84 enzymes and was named UGT84A57. The recombinant enzyme of WjGT1 expressed in Escherichia coli showed C-glucosylation activity toward the 6-position of flavones such as apigenin and luteolin. The enzyme also showed significant activity toward flavonols, but trace or no activity toward flavone 4'-O-glucosides, suggesting that isosaponarin biosynthesis in wasabi plants would proceed by 6-C-glucosylation of apigenin, followed by its 4'-O-glucosylation. Interestingly, the enzyme showed no activity against sinapic acid or p-coumaric acid, which are usually the main substrates of UGT84 enzymes. The accumulation of WjGT1 transcripts was observed mainly in the leaves and flowers of wasabi, in which C-glucosylflavones were accumulated. Molecular phylogenetic analysis suggested that WjGT1 acquired C-glycosylation activity independently from other reported CGTs after the differentiation of the family Brassicaceae.

Efficient modification of the Pseudomonas aeruginosa toxin 2-heptyl-1-hydroxyquinolin-4-one by three Bacillus glycosyltransferases with broad substrate ranges

Glycosylation of natural and synthetic products can alter the physical, chemical and pharmacological properties of the aglycon. Conversion of 2-heptyl-1-hydroxyquinolin-4-one (HQNO), a potent respiratory inhibitor produced by Pseudomonas aeruginosa, to the less toxic 2-heptyl-1-(β-D-glucopyranosydyl)-quinolin-4-one, was recently demonstrated for Bacillus subtilis strain 168. In this study, we compared the genomes of several Bacillus spp. to identify candidate enzymes for HQNO glucosylation. All three (putative) UDP-glycosyltransferases (GT) of B. subtilis 168 tested, YjiC, YdhE and YojK, were capable of HQNO glucosylation, with YjiC showing the highest turnover rate (k_cat) of 4.6 s^-1, and YdhE exhibiting the lowest K_m value for HQNO of 9.1 μM. All three GT predominantly utilized UDP-glucose, but YdhE was similarly active with TDP-glucose. Among the aglycons tested, HQNO was the preferred substrate of all three GT, but they also showed activities toward the P. aeruginosa exoproducts pyocyanin, 2-heptyl-3-hydroxyquinolin-4(1H)-one (the Pseudomonas quinolone signal) and 2,4-dihydroxyquinoline, the plant derived antimicrobials vanillin and quercetin, and the macrolide antibiotic tylosin A. Our results underline the promiscuity and substrate flexibility of YjiC, YdhE and YojK, and suggest a physiological role in natural toxin resistance of B. subtilis. Especially YdhE appears to be an attractive biocatalyst for the glycoengineering of natural products.

Transcriptome characterization and differentially expressed genes under flooding and drought stress in the biomass grasses Phalaris arundinacea and Dactylis glomerata

BACKGROUND AND AIMS

Perennial grasses are a global resource as forage, and for alternative uses in bioenergy and as raw materials for the processing industry. Marginal lands can be valuable for perennial biomass grass production, if perennial biomass grasses can cope with adverse abiotic environmental stresses such as drought and waterlogging.

METHODS

In this study, two perennial grass species, reed canary grass (Phalaris arundinacea) and cocksfoot (Dactylis glomerata) were subjected to drought and waterlogging stress to study their responses for insights to improving environmental stress tolerance. Physiological responses were recorded, reference transcriptomes established and differential gene expression investigated between control and stress conditions. We applied a robust non-parametric method, RoDEO, based on rank ordering of transcripts to investigate differential gene expression. Furthermore, we extended and validated vRoDEO for comparing samples with varying sequencing depths.

KEY RESULTS

This allowed us to identify expressed genes under drought and waterlogging whilst using only a limited number of RNA sequencing experiments. Validating the methodology, several differentially expressed candidate genes involved in the stage 3 step-wise scheme in detoxification and degradation of xenobiotics were recovered, while several novel stress-related genes classified as of unknown function were discovered.

CONCLUSIONS

Reed canary grass is a species coping particularly well with flooding conditions, but this study adds novel information on how its transcriptome reacts under drought stress. We built extensive transcriptomes for the two investigated C3 species cocksfoot and reed canary grass under both extremes of water stress to provide a clear comparison amongst the two species to broaden our horizon for comparative studies, but further confirmation of the data would be ideal to obtain a more detailed picture.

Tomato glycosyltransferase Twi1 plays a role in flavonoid glycosylation and defence against virus

BACKGROUND

Secondary metabolites play an important role in the plant defensive response. They are produced as a defence mechanism against biotic stress by providing plants with antimicrobial and antioxidant weapons. In higher plants, the majority of secondary metabolites accumulate as glycoconjugates. Glycosylation is one of the commonest modifications of secondary metabolites, and is carried out by enzymes called glycosyltransferases.

RESULTS

Here we provide evidence that the previously described tomato wound and pathogen-induced glycosyltransferase Twi1 displays in vitro activity toward the coumarins scopoletin, umbelliferone and esculetin, and the flavonoids quercetin and kaempferol, by uncovering a new role of this gene in plant glycosylation. To test its activity in vivo, Twi1-silenced transgenic tomato plants were generated and infected with Tomato spotted wilt virus. The Twi1-silenced plants showed a differential accumulation of Twi1 substrates and enhanced susceptibility to the virus.

CONCLUSIONS

Biochemical in vitro assays and transgenic plants generation proved to be useful strategies to assign a role of tomato Twi1 in the plant defence response. Twi1 glycosyltransferase showed to regulate quercetin and kaempferol levels in tomato plants, affecting plant resistance to viral infection.

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.

A specific UDP-glucosyltransferase catalyzes the formation of triptophenolide glucoside from Tripterygium wilfordii Hook. f

Tripterygium wilfordii Hook. f. is a perennial woody vine member of the Celastraceae family. As a traditional Chinese medicine, it contains complex chemical components and exerts various pharmacological activities. In the present study, we identified a glucosyltransferase, TwUGT1, that can catalyze the synthesis of an abietane-type diterpene glucoside, namely, triptophenolide14-O-beta-D-glucopyranoside, and investigated the pharmacological activity of triptophenolide glucoside in diverse cancer cells. Triptophenolide glucoside exhibited significant inhibitory effects on U87-MG, U251, C6, MCF-7, HeLa, K562, and RBL-2H3 cells as determined by pharmacological analysis. The triptophenolide glucoside content of T. wilfordii was analyzed using Agilent Technologies 6490 Triple Quad LC/MS. The glucosyltransferase TwUGT1 belongs to subfamily 88 and group E in family 1. Molecular docking and site-directed mutagenesis of TwUGT1 revealed that the His30, Asp132, Phe134, Thr154, Ala370, Leu376, Gly382, His387, Glu395 and Gln412 residues play crucial roles in the catalytic activity of triptophenolide 14-O-glucosyltransferase. In addition, TwUGT1 was also capable of glucosylating phenolic hydroxyl groups, such as those in liquiritigenin, pinocembrin, 4-methylumbelliferone, phloretin, and rhapontigenin.

Network-based feature selection reveals substructures of gene modules responding to salt stress in rice

Rice, an important food resource, is highly sensitive to salt stress, which is directly related to food security. Although many studies have identified physiological mechanisms that confer tolerance to the osmotic effects of salinity, the link between rice genotype and salt tolerance is not very clear yet. Association of gene co-expression network and rice phenotypic data under stress has penitential to identify stress-responsive genes, but there is no standard method to associate stress phenotype with gene co-expression network. A novel method for integration of gene co-expression network and stress phenotype data was developed to conduct a system analysis to link genotype to phenotype. We applied a LASSO-based method to the gene co-expression network of rice with salt stress to discover key genes and their interactions for salt tolerance-related phenotypes. Submodules in gene modules identified from the co-expression network were selected by the LASSO regression, which establishes a linear relationship between gene expression profiles and physiological responses, that is, sodium/potassium condenses under salt stress. Genes in these submodules have functions related to ion transport, osmotic adjustment, and oxidative tolerance. We argued that these genes in submodules are biologically meaningful and useful for studies on rice salt tolerance. This method can be applied to other studies to efficiently and reliably integrate co-expression network and phenotypic data.

Rice sulfoquinovosyltransferase SQD2.1 mediates flavonoid glycosylation and enhances tolerance to osmotic stress

Sulfoquinovosyltransferase 2 (SQD2) catalyses the final step in the sulfoquinovosyldiacylglycerol (SQDG) biosynthetic pathway. It is involved in the phosphate starvation response. Here, we show that rice SQD2.1 has dual activities catalysing SQDG synthesis and flavonoid glycosylation. SQD2.1 null mutants (sqd2.1) in rice had decreased levels of glycosidic flavonoids, particularly apigenin 7-O-glucoside (A7G), whereas these metabolites were increased in rice plants overexpressing SQD2.1. The sqd2.1 mutants and SQD2.1 overexpressing lines showed reduced and enhanced, respectively, tolerance to salinity and drought. Treating the sqd2.1 mutants with A7G decreased oxidative damage and restored stress tolerance to the wild-type levels. These findings demonstrate that SQD2.1 has a novel function in the glycosylation of flavonoids that is required for osmotic stress tolerance in rice. The novel activity of SQD2.1 in the production of glycosidic flavonoids improves scavenging of reactive oxygen species and protects against excessive oxidation.

Crystal structures of rhamnosyltransferase UGT89C1 from Arabidopsis thaliana reveal the molecular basis of sugar donor specificity for UDP-β-l-rhamnose and rhamnosylation mechanism

Glycosylation is a key modification for most molecules including plant natural products, for example, flavonoids and isoflavonoids, and can enhance the bioactivity and bioavailability of the natural products. The crystal structure of plant rhamnosyltransferase UGT89C1 from Arabidopsis thaliana was determined, and the structures of UGT89C1 in complexes with UDP-β-l-rhamnose and acceptor quercetin revealed the detailed interactions between the enzyme and its substrates. Structural and mutational analysis indicated that Asp356, His357, Pro147 and Ile148 are key residues for sugar donor recognition and specificity for UDP-β-l-rhamnose. The mutant H357Q exhibited activity with both UDP-β-l-rhamnose and UDP-glucose. Structural comparison and mutagenesis confirmed that His21 is a key residue as the catalytic base and the only catalytic residue involved in catalysis independently as UGT89C1 lacks the other catalytic Asp that is highly conserved in other reported UGTs and forms a hydrogen bond with the catalytic base His. Ser124 is located in the corresponding position of the catalytic Asp in other UGTs and is not able to form a hydrogen bond with His21. Mutagenesis further showed that Ser124 may not be important in its catalysis, suggesting that His21 and acceptor may form an acceptor-His dyad and UGT89C1 utilizes a catalytic dyad in catalysis instead of catalytic triad. The information of structure and mutagenesis provides structural insights into rhamnosyltransferase substrate specificity and rhamnosylation mechanism.