A genome-wide phylogenetic reconstruction of family 1 UDP-glycosyltransferases revealed the expansion of the family during the adaptation of plants to life on land

Glycosyltransferases: Pioneering roles in agriculture and medicine

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

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

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

Functional Characterization of 5-O-Glycosyltranferase Transforming 3-O Anthocyanins into 3,5-O Anthocyanins in Freesia hybrida

Floral coloration in Freesia hybrida is predominantly attributed to anthocyanins, with glycosylation playing a critical role in their stability and diversity. This study investigates the molecular mechanisms underlying color variation between F. hybrida cultivars, focusing on anthocyanin 5-O-glucosyltransferases (An5GTs). HPLC analysis revealed that 'Pink Passion' petals accumulate 3,5-O-diglucosidic anthocyanins, absent in 'Red River®' and 'Ambiance'. RNA-seq identified seven candidate Fh5GT genes, with phylogenetic and subcellular localization analyses confirming their classification as cytosolic glycosyltransferases. Expression profiling highlighted elevated transcript levels of Fh5GT1, Fh5GT3, and Fh5GT7 in 'Pink Passion', correlating with its di-glucosidic anthocyanin accumulation. In vitro enzymatic assays demonstrated that Fh5GT3 and Fh5GT7 preferentially glucosylate 3-O-monoglucosidic anthocyanins to form stable 3,5-O-diglucosides, with minimal activity on anthocyanidins to generate 5-O-glucosidic anthocyanins. Heterologous expression of Fh5GT3 and Fh5GT7 in Arabidopsis complemented anthocyanin deficiency in 5gt mutants, restoring pigmentation. These findings elucidate the potential role of 5GTs in modulating floral color diversity through anthocyanin modification, providing insights for targeted breeding strategies to enhance ornamental traits in horticultural species.

Identification and characteristic analysis of PavUGT48 as a novel UDP-glycosyltransferase with dual functions on anthocyanin and amygdalin biosynthesis in sweet cherry

UDP-glycosyltransferase (UGT) is essential for fruit development, but its specific role in sweet cherry fruits has not been clearly defined. This study identified a new differentially expressed UGT gene, FUN_010048, by analyzing transcriptomic data from various colored regions of bicolored fruits. The 187 UGT family members were identified in the sweet cherry genome of 'Tieton'. Notably, FUN_010084 has been renamed PavUGT48. Expression analysis revealed that PavUGT48 increased during the development of the differently colored sweet cherry fruits. Co-expression network analysis and further experiments confirmed that PavUGT48 generates cyanidin-3-O-glucoside from cyanidin using UDP-glucose (UDP-Glc) as the sugar donor, enhancing fruit coloration. Additionally, PavUGT48 facilitates the formation of amygdalin from prunasin, but it does not react with naringenin, dihydrokaempferol, or kaempferol when UDP-Glc serves as the sugar donor. These findings enhance our understanding of UGT enzymes in sweet cherries and provide a basis for improving fruit quality and developing new varieties.

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

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

Characterization of a 4'-O-rhamnosyltransferase and de novo biosynthesis of bioactive steroidal triglycosides from Paris polyphylla

Steroidal saponins in Paris polyphylla featuring complicated sugar chains exhibit notable biological activities, but their sugar-chain biosynthesis is still not fully understood. Here, we identified a 4'-O-rhamnosyltransferase (UGT73DY2) from P. polyphylla, which catalyzes the 4'-O-rhamnosylation of polyphyllins V and VI, producing dioscin and pennogenin 3-O-β-chacotrioside, respectively. UGT73DY2 exhibits strict substrate specificity toward steroidal diglycosides and UDP-rhamnose, and a new steroidal triglycoside can be synthesized through enzyme catalysis. A mutation library was generated based on semi-rational design, identifying three mutants, I358T, A342V, and A132T, which displayed approximately two-fold enhanced enzyme activity. Molecular dynamics simulations revealed that shortened distances between the 4'-OH group of the sugar acceptor and either the crucial residue H20 or the donor UDP-Rha contribute to the enhanced enzyme activity. Moreover, subcellular localization analysis of UGT73DY2 and other biosynthetic enzymes indicated that dioscin biosynthesis predominantly occurs in the endoplasmic reticulum of plant cells. By co-expressing 14 biosynthetic genes in Nicotiana benthamiana, optimizing HMGR subcellular localization and cytochrome P450 gene sets, and engineering UGT73DY2, we successfully established a dioscin biosynthesis system with a yield of 3.12 ± 0.11 μg/g dry weight. This study not only clarifies the 4'-O-rhamnosylation process in steroidal saponin biosynthesis but also presents an alternative approach for the production of steroidal saponins in P. polyphylla through synthetic biology and metabolic engineering.

Functional characterization of a maize UDP-glucosyltransferase involved in the biosynthesis of flavonoid 7-O-glucosides and di-O-glucosides

Flavonoids are glycosylated in the final steps of their synthesis by UDP-dependent glycosyltransferase enzymes. We present the functional characterization of the first maize flavonoid O-glucosyltransferase enzyme from family 85, which exhibits properties not previously described. ZmUGT85W2 catalyzes the O-glucosylation of flavonols, flavones and flavanones, to form primarily 7-O-glucosides, but also flavonol O-glucoside positional isomers, flavones and flavonol di-O-glucosides. ZmUGT85W2 exhibited a differential kinetic behavior depending on the flavonoid acceptor, showing hyperbolic dependence for flavonols and sigmoidal response for flavanones and flavones. Structural and molecular docking analyses predicted conserved residues interacting with the sugar donor, with close contact with the 7-hydroxyl of the flavonoid acceptors, consistent with enzymatic activity results. In addition, ZmUGT85W2 is induced by UV-B radiation, and its expression is controlled by the B and PL1 transcription factors. Consistently, higher levels of flavone and flavonol O-glycosides are accumulated in leaves of plants exposed to solar UV-B compared to control plants, suggesting that ZmUGT85W2 is involved in the biosynthesis of these metabolites in maize leaves, contributing to UV-B tolerance. The activity of ZmUGT85W2, along with its elevated expression in silks and pericarps expressing the R2R3-MYB transcription factor P1, highlights its critical role in the accumulation of flavonoid O-glucosides in these tissues. Together, our findings reveal a key step in maize flavonoid O-glycosides biosynthesis, with the observed positive cooperative behaviors suggesting that ZmUGT85W2 plays a crucial role in finely regulating metabolic flux towards these compounds in planta.

Identification and functional characterization of a new flavonoid glycosyltransferase from Rheum palmatum

Objective

To characterize a glycosyltransferase (RpUGT1) from Rheum palmatum and investigate its specificity toward flavonoid compounds.

Methods

The RpUGT1 was expressed in Escherichia coli and screened for catalytic activity against a range of flavonoid substrates using a high-throughput HPLC assay method. Mass spectrometry (MS) and nuclear magnetic resonance (NMR) were used to determine the structure of the product. Homology modeling, molecular docking analyses and site-directed mutagenesis studies were conducted to identify key residues responsible for its function.

Results

The recombinant RpUGT1 protein exhibited catalytic activity towards various flavonoids. Notably, RpUGT1 catalyzed the glycosylation of isorhamnetin to form 3-O-glucoside and kaempferol to form 7-O-glucoside, utilizing uridine diphosphate (UDP) glucose as the sugar donor. The homology modeling and molecular docking analyses identified key residues responsible for its activity. Subsequent site-directed mutagenesis studies highlighted the crucial role of K307 in catalysis.

Conclusion

These discoveries offer valuable perspectives on the role of the UGT family and establish a groundwork for forthcoming research on the synthesis of flavonoids in plants.

Genomics of sterols biosynthesis in plants: Current status and future prospects

Sterols produced by bacteria and all eukaryotic organisms are essential for membrane functionality and stability. They play a vital role in growth, development and in abiotic stress tolerance. They are involved in diverse responses to biotic and abiotic stresses that lead to providing resistance against multiple diseases. Additionally, sterols serve as defensive compounds against herbivorous insects and animals. Phytosterols derived from plants, improve human nutrition and health and cure different ailments. The biosynthetic pathways for sterols and triterpenes exhibit similarities until the synthesis of 2,3-oxidosqualene. The complexity of sterol pathways increases during the advanced stages of polycyclic structure synthesis, and remain poorly comprehended in plants. This review explores the various omics techniques used to unveil the functions of genes associated with the phytosterol pathways. The study investigates the biosynthetic gene clusters to clarify the structural arrangements of genes linked to metabolic pathways. Both the upstream and downstream genes associated with these pathways, as well as their evolutionary connections and interrelations within the pathways were brought to the forefront. Moreover, developing strategies to unravel the biosynthesis completely and their multi-layered regulation are crucial to comprehend the global roles that sterols play in plant growth, development, stress tolerance and in imparting defence against pathogens.

Comprehensive mutant chemotyping reveals embedding of a lineage-specific biosynthetic gene cluster in wider plant metabolism

Plants produce diverse specialized metabolites with important ecological functions. It has recently become apparent that the genes for many of these pathways are not dispersed in plant genomes, but rather are arranged like beads on a string in biosynthetic gene clusters (BGCs). Pathways encoded by BGCs are as a rule dedicated linear pathways that do not form parts of wider metabolic networks. In contrast, the genes for the biosynthesis of widely distributed more ancestral metabolites such as carotenoids and anthocyanins are not clustered. Little is known about how these more recently evolved clustered pathways interact with general plant metabolism. We recently characterized a 12-gene BGC for the biosynthesis of the antimicrobial defense compound avenacin A-1, a triterpene glycoside produced by oats. Avenacin A-1 is acylated with the fluorophore N-methyl anthranilate and confers bright blue fluorescence of oat root tips under ultraviolet light. Here, we exploit a suite of >100 avenacin-deficient mutants identified by screening for reduced root fluorescence to identify genes required for the function of this paradigm BGC. Using a combination of mutant chemotyping, biochemical and molecular analysis, and genome resequencing, we identify two nonclustered genes (Sad4 and Pal2) encoding enzymes that synthesize the donors required for avenacin glycosylation and acylation (recruited from the phenylpropanoid and tryptophan pathways). Our finding of these Cluster Auxiliary Enzymes (CAEs) provides insights into the interplay between general plant metabolism and a newly evolved lineage-specific BGC.

Genome-wide identification of the UGT genes family in Acer rubrum and role of ArUGT52 in anthocyanin biosynthesis under cold stress

Acer rubrum is a widespread Acer species valued for its vibrant autumn foliage. The UGT (UDP-glycosyltransferase) gene family is integral to the biosynthesis of anthocyanins, the pigments responsible for leaf coloration. This study aimed to comprehensively identify and characterize the UGT gene family in the A. rubrum genome. The results of the phylogenetic analysis of 249 ArUGTs revealed 18 distinct subgroups. Conserved motif analysis demonstrated structural similarities within subgroups. Gene duplication analysis identified 21 tandem and 66 segmental duplication events across chromosomes. Transcriptomic data from autumn leaves of different colours and under low-temperature stress were analyzed for ArUGT expression patterns. Compared to controls, 44 UGTs were upregulated and 99 downregulated in yellow leaves, while 59 were upregulated and 84 downregulated in red leaves. Low-temperature treatments showed upregulation of 18 UGTs at 10 °C and 40 UGTs at 4 °C. Downregulation was observed in 7 UGTs at 10 °C and 33 UGTs at 4 °C. Among all UGT genes, ArUGT52 was common in highly expressed genes in both red leaf and low-temperature stress. Furthermore, the transient overexpression of ArUGT52 in tobacco plants demonstrated cytoplasmic localization and a marked increase in anthocyanin levels under cold stress. In vitro, biochemical assay results indicated that the ArUGT52 was involved in anthocyanin biosynthesis via the glucosylation of anthocyanidins. This study provides insights into the genetic mechanisms of leaf coloration and the potential of UGT manipulation for enhancing plant responses to low-temperature stress. These findings have applications in ornamental horticulture and agriculture.

Functional Characterization of a Highly Efficient UDP-Glucosyltransferase CitUGT72AZ4 Involved in the Biosynthesis of Flavonoid Glycosides in Citrus

Citrus is an important dietary source of flavonoid glycosides, and UDP-glycosyltransferases (UGTs) are the key enzymes responsible for their glycosylation. In this study, a genome-wide analysis of the CitUGT gene family was conducted to identify CitUGTs that contribute to flavonoid 4'-O-glucosides biosynthesis. Our analysis identified 136 CitUGTs in the Citrus clementina genome, classifying them into 18 phylogenetic groups (A-R) and 25 families. This classification was strongly supported by consistent gene structures and motif patterns. Moreover, we identified a CitUGT gene (Ciclev10025462m, designated CitUGT72AZ4) that encodes flavonoid 4'-O-glucosyltransferase for the first time in citrus. This enzyme preferentially glycosylated the 4'-OH group of multiple flavonoids, exhibiting higher catalytic efficiency toward quercetin and three flavones in vitro. Virus-induced gene silencing of CitUGT72AZ4 significantly decreased the accumulation of flavonoid 4'-O-glucosides. These results indicated that CitUGT72AZ4 participated in the biosynthesis of flavonoid 4'-O-glucoside in citrus. Overall, our findings provide valuable insights into the CitUGT gene family and contribute to its functional characterization.

Genome-wide identification of UDP-glycosyltransferases involved in flavonol glycosylation induced by UV-B irradiation in Eriobotrya japonica

Flavonol glycosides are secondary metabolites important for plant development and stress defense such as UV-B irradiation. UDP-glycosyltransferase (UGT) catalyzes the last step in the biosynthesis of flavonol glycosides. Eriobotrya japonica is abundant in flavonol glycosides, but UGTs responsible for accumulation of flavonol glycosides remain unknown. Here, 13 flavonol glycosides including monoglycosides and diglycosides were characterized in different tissues of loquat by LC-MS/MS. UV-B irradiation significantly increased the accumulation of four quercetin glycosides and two kaempferol glycosides in loquat fruit. Based on UGT gene family analysis, transcriptome analysis, enzyme assays of recombinant proteins as well as transient overexpression assays in Nicotiana benthamiana, three UGTs were identified, i.e. EjUGT78T4 as flavonol 3-O-galactosyltransferase, EjUGT78S3 as flavonol 3-O-glucosyltransferase, and EjUGT91AK7 as flavonol 1 → 6 rhamnosyltransferase. This work elucidates the formation of flavonol glycosides in loquat through UGT-mediated glycosylation.

Insights into functional divergence, catalytic versatility and specificity of small molecule glycosyltransferases

Glycosylation is one of the most fundamental biochemical processes in cells. It plays crucial roles in diversifying plant natural products for structures, bioavailability and bioactivity, and thus, renders the glycosylated compounds valuable as food additives, nutraceuticals and pharmaceuticals. Moreover, glycosylated compounds impact plant growth, development and stress response. Therefore, understanding the biochemical function of the glycosyltransferases (GTs) is crucial to the elucidation of natural product biosynthetic pathways, improving plant traits and development of processes for industrially-important compounds. UDP-dependent glycosyltransferases (UGTs) that belong to the glycosyltransferase family-1 (GT1) and catalyze the transfer of glycosyl moieties from UDP-sugars to various small molecules, are the key players in natural product glycosylation. Recent studies also found the involvement of non-canonical cellulose synthase-like (CesAs) and glycosyl hydrolase (GH) family enzymes in the glycosylation of plant specialized metabolites. Decades of research on GTs provided critical insights into catalytic mechanism, substrate/product specificity and catalytic promiscuity, but biochemical function and physiological roles of GTs in majority of the natural product biosynthetic pathways remain to be understood. It is also important to redefine high-throughput strategies of GT mining to uncover novel biochemical function, considering that GTs are the large superfamily members in plants and other organisms. This review underscores the roles of GTs in small molecule glycosylation, plant development and stress responses, highlighting the catalytic versatility and substrate/product specificity of GTs in shaping plant metabolic diversity, and discusses the emerging strategies for mining of uncharacterized GTs to unravel biochemical and physiological functions and to elucidate natural product biosynthetic pathways.

Multi-omics analysis reveals the role of UGT72 family genes in arbutin biosynthesis in Pyrus and evolution driven by whole genome duplication

The UGT72 gene family encodes proteins that glycosylate phenylpropanoids, and thus contribute to the synthesis of various phenolic substances. However, their functional role and evolutionary history in Pyrus spp. remains poorly understood. Here we explored the evolution, amplification, coding region structural variation, and functional divergence of the UGT72 gene family and its subfamilies. Further, we identified functional genes involved in arbutin synthesis and functionally validated the key genes. 15 UGT72 genes were identified in the complete genome sequence and classified into two subfamilies of Pyrus betulifolia. Significant expansion of the UGT72 gene family occurred after genome duplication in P. betulifolia. 53.33 % of all UGT72 family genes were found to have undergone expansion via WGD/segmental duplication. A noteworthy discovery was that the amplification of functional genes such as PbUGT72B1714 during polyploidization, combined with the loss of vital motifs and variations at important sites within these genes, significantly impacted the diversification of arbutin metabolism. These findings offer novel insights into how gene gains and losses caused by WGDs have contributed to metabolic diversification and evolutionary adaptation in Pyrus, as well as a groundwork for more detailed investigations into the mechanisms of arbutin metabolism.

Investigation of the potential regulation of the UDP-glycosyltransferase genes on rice grain size and abiotic stress response

Uridine diphosphate (UDP) glycosyltransferases (UGTs) are widely involved in various metabolic processes. In the present study, we performed a genome-wide survey and identified 199 Oryza sativa UGT genes (OsUGTs), which were classified into 17 groups. We showed that tandem duplication played a major role in the expansion of the OsUGT family, which experienced purifying selection during the evolution process. 163 OsUGTs were expressed in at least one of the six tested tissues, and were clustered into three groups according to their tissue expression profiles. By using the RFGB database, we identified different haplotypes of seven OsUGTs that were highly expressed in seeds, and showed significant differences in grain size among different haplotypes. Moreover, our results also uncovered differential responses of OsUGTs expression to abiotic stresses and hormone treatments, including drought, salt, cold, heat, ABA, JA and AUXIN. By using quantitative real-time PCR, we further confirmed the differential expression of nine selected OsUGTs under ABA, JA, salt, drought and cold treatments, among which OsUGT5 and OsUGT182 were induced by all these five treatments. Our results provide insight into the role of several UGT genes for physiological responses, which will facilitate to investigate their function in regulating rice development and abiotic stress responses.

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

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

Genome-wide screen and multi-omics analysis reveal OGT1 participate in the biosynthesis of safflower flavonoid glycosides

Safflower, an economic crop, is renowned for its flowers, which are widely used in medicines for treating cardiovascular and cerebrovascular diseases and in dyes for food and industry. The utility of safflower depends on its flavonoid glycosides. Therefore, the biosynthesis of safflower flavonoid glycosides has been a focus of attention, but the present mechanisms remain poorly understood. This study aims to identify functional genes associated with flavonoid glycoside biosynthesis in safflower through a comprehensive approach that integrates whole-genome screen and multi-omics correlation studies. CYP and UGT are two crucial genes families involved in flavonoid glycoside biosynthesis. We have screened 264 CYP genes and 140 UGT genes in the genome of safflower and conducted analyzes including phylogenetic relationships, conserved motifs, gene structures, cis-acting elements, and chromosome mapping, which provided extensive and comprehensive data on the CYP and UGT gene families. Integration of phenotype and metabolic data from safflower different tissues helped narrow down the screening by confirming that HSYA is synthesized only in flowers. Based on the gene expression patterns and phylogenetic analysis, CtOGT1 was ultimately identified, which could catalyze the generation of glycosides using various flavonoid substrates and exhibited strong substrate affinity. Moreover, molecular docking studies elucidated CtOGT1's highly active intrinsic mechanism. In conclusion, this study effectively identified genes responsible for flavonoid glycoside biosynthesis in safflower through the integration of whole-genome screen and multi-omics analysis, established a comprehensive foundation of data, methodology, and experimental evidence for further elucidating the pathways of safflower flavonoid glycoside biosynthesis.

Multi-omics analysis reveals promiscuous O-glycosyltransferases involved in the diversity of flavonoid glycosides in Periploca forrestii (Apocynaceae)

Flavonoid glycosides are widespread in plants, and are of great interest owing to their diverse biological activities and effectiveness in preventing chronic diseases. Periploca forrestii, a renowned medicinal plant of the Apocynaceae family, contains diverse flavonoid glycosides and is clinically used to treat rheumatoid arthritis and traumatic injuries. However, the mechanisms underlying the biosynthesis of these flavonoid glycosides have not yet been elucidated. In this study, we used widely targeted metabolomics and full-length transcriptome sequencing to identify flavonoid diversity and biosynthetic genes in P. forrestii. A total of 120 flavonoid glycosides, including 21 C-, 96 O-, and 3 C/O-glycosides, were identified and annotated. Based on 24,123 full-length coding sequences, 99 uridine diphosphate sugar-utilizing glycosyltransferases (UGTs) were identified and classified into 14 groups. Biochemical assays revealed that four UGTs exhibited O-glycosyltransferase activity toward apigenin and luteolin. Among them, PfUGT74B4 and PfUGT92A8 were highly promiscuous and exhibited multisite O-glycosylation or consecutive glycosylation activities toward various flavonoid aglycones. These four glycosyltransferases may significantly contribute to the diversity of flavonoid glycosides in P. forrestii. Our findings provide a valuable genetic resource for further studies on P. forrestii and insights into the metabolic engineering of bioactive flavonoid glycosides.

A novel QTL qRYM-7H for barley yellow mosaic resistance identified by GWAS and linkage analysis

Barley (Hordeum vulgare L.) is the fourth largest cereal crop in the world after rice, wheat and maize. Barley yellow mosaic disease (BYMD) is a serious threat to winter barley production. The evolution and mutation of virus strains lead to the breakdown of the resistance of the originally resistant varieties. It is therefore vital to explore new BYMD resistance genes. In this study, a natural population (334 barley varieties or lines) and a double haploid population derived from the cross between Tam407227 and Franklin were used to search for new quantitative trait loci (QTL) for BYMD resistance. Two major QTL on chromosomes 3H and 7H, respectively, were detected from the genome wide association study and validated in the DH population. Among them, The QTL on 3H (qRYM-3H/qTFRYM-3H) was confirmed to be the reported BYMD resistance gene eIF4E by haplotype analysis. And the QTL on 7H (qRYM-7H/qTFRYM-7H) is a novel QTL that has not been reported before. Another QTL on 2H was identified from the DH population. This QTL is more likely the Rmy16Hb reported previously. These three QTL showed an additive effect on improving BYMD resistance with the average disease scores from 2.45 (all sensitive alleles for these three QTL) to 0.62 (all tolerant alleles for these three QTL). The candidate genes for the novel QTL qRYM-7H/qTFRYM-7H were predicted based on transcriptome sequencing and qPCR analysis.

Genome-wide analysis of UDP-glycosyltransferase family in Citrus sinensis and characterization of a UGT gene encoding flavonoid 1-2 rhamnosyltransferase

UDP-glycosyltransferases (UGTs) play a crucial role in the glycosylation of secondary metabolites in plants, which is of significant importance for growth and response to biotic or abiotic stress. Despite the wide identification of UGT family members in various species, limited information is available regarding this family in citrus. In this study, we identified 87 UGT genes from the Citrus sinensis genome and classified them into 14 groups. We characterized their gene structures and motif compositions, providing insights into the molecular basis underlying discrepant functions of UGT genes within each evolutionary branch. Tandem duplication events were found to be the main driving force behind UGT gene expansion. Additionally, we identified numerous cis-acting elements in the promoter region of UGT genes, including those responsive to light, growth factors, phytohormones, and stress conditions. Notably, light-responsive elements were found with a frequency of 100 %. We elucidated the expression pattern of UGTs during fruit development in Citrus aurantium using RNA-seq and quantitative real-time PCR (qRT-PCR), revealing that 10 key UGT genes are closely associated with biosynthesis of bitter flavanone neohesperidosides (FNHs). Furthermore, we identified Ca1,2RhaT as a flavonoid 1-2 rhamnosyltransferase (1,2RhaT) involved in FNHs biosynthesis for the first time. Isolation and functional characterization of the gene Ca1,2RhaT from Citrus aurantium in vitro and in vivo indicated that Ca1,2RhaT encoded a citrus 1,2RhaT and possessed rhamnosyl transfer activities. This work provides comprehensive information on the UGT family while offering new insights into understanding molecular mechanisms regulating specific accumulation patterns of FNHs or non-bitter flavanone rutinosides (FRTs) in citrus.

Characterization of UGT71, a major glycosyltransferase family for triterpenoids, flavonoids and phytohormones-biosynthetic in plants

UGT catalyzes the transfer of glycosyl molecules from donors to acceptors, and the glycosylation catalyzed by them is a modification reaction essential for plant cell growth, development, and metabolic homeostasis. Members of this class of enzymes are found in all areas of life and are involved in the biosynthesis of an extensive range of glycosides. This review aims to screen and collate relevant properties of the UGT71 family in plants and their functions in plant secondary metabolites. Firstly, we conducted a retrospective analysis of information about plant UGTs, before focusing on UGT71s through glycosylation of secondary metabolites (triterpenoids, flavonoids) and glycosylation of phytohormones (ABA, SA). Consequently, they play a pivotal role in plant defence, hormone regulation, and the biosynthesis of secondary metabolites, thereby enabling plants to adapt to changing environments. Further investigation revealed that UGTs (UGT71s) can enhance the adaptive and resistant potential of plants in the context of today's deteriorating growing conditions due to climate change impacts caused by global warming. Nevertheless, further in-depth studies on the intricate interactions among UGTs in plants are required to fully exploit the potential of UGTs in protecting plants against stress.

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

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

Identification of putative genes for caffeoylated flavonoid glycoside biosynthesis in Pseudognaphalium affine

Pseudognaphalium affine (D. Don) Anderberg, commonly found in East Asia, has extensive applications as both a traditional medicine and a vegetable in China. The caffeoylated flavonoid glycosides produced by P. affine exhibit remarkable anti-complement activities. Although these compounds have potential therapeutic value, the biosynthetic pathway responsible for their production remains largely unknown. To elucidate the key catalytic steps involved in caffeoylated flavonoid glycoside biosynthesis, we conducted a comprehensive analysis of the full-length transcriptome of P. affine. Further phylogenetic tree analysis predicted potential UDP glycosyltransferase (UGT) and BAHD acyltransferase (BAHD-AT) related with caffeoylated flavonoid glycoside biosynthesis. Subsequently, enzyme assay led to the discovery of PaUGT23 as a key enzyme responsible for the glycosylation of hydroxy groups in flavonoids, resulting in the formation of luteolin-4'-O-glucoside, luteolin-7-O-glucoside, quercetin-4'-O-glucoside, quercetin-7-O-glucoside, and apigenin-7-O-glucoside, while PaBAHD21 was found to catalyze the caffeoylation of flavonoid glycosides, resulting in the formation of luteolin 4'-O-β-D-(6″-E-caffeoyl)-glucopyranoside, quercetin 4'-O-β-D-(6″-E-caffeoyl)-glucopyranoside, apigenin 4'-O-β-D-(6″-E-caffeoyl)-glucopyranoside and apigenin 7-O-β-D-(6″-E-caffeoyl)-glucopyranoside. Moreover, their catalytic activities were verified in vivo by transient transfection experiment. This study presents the first comprehensive analysis of the full-length transcriptome in P. affine, providing significant insights into the biosynthesis and accumulation mechanisms of bioactive caffeoylated flavonoid glycosides.

Unveiling the Power of Flax Lignans: From Plant Biosynthesis to Human Health Benefits

BACKGROUND

Flax (Linum usitatissimum L.) is the richest plant source of lignin secondary metabolites. Lignans from flax have been applied in the fields of food, medicine, and health due to their significant physiological activities. The most abundant lignan is secoisolariciresinol, which exists in a glycosylated form in plants.

RESULTS

After ingestion, it is converted by human intestinal flora into enterodiol and enterolactone, which both have physiological roles. Here, the basic structures, contents, synthesis, regulatory, and metabolic pathways, as well as extraction and isolation methods, of flax lignans were reviewed. Additionally, the physiological activity-related mechanisms and their impacts on human health, from the biosynthesis of lignans in plants to the physiological activity effects observed in animal metabolites, were examined.

CONCLUSIONS

The review elucidates that lignans, as phenolic compounds, not only function as active substances in plants but also offer significant nutritional values and health benefits when flax is consumed.

A multiscale approach to understanding the shared blue-orange flower color polymorphism in two Lysimachia species

BACKGROUND

Polymorphisms are common in nature, but they are rarely shared among closely related species. Polymorphisms could originate through convergence, ancestral polymorphism, or introgression. Although shared neutral genomic variation across species is commonplace, few examples of shared functional traits exist. The blue-orange petal color polymorphisms in two closely related species, Lysimachia monelli and L. arvensis were investigated with UV-vis reflectance spectra, flavonoid biochemistry, and transcriptome comparisons followed by climate niche analysis.

RESULTS

Similar color morphs between species have nearly identical reflectance spectra, flavonoid biochemistry, and ABP gene expression patterns. Transcriptome comparisons reveal two orange-specific genes directly involved in both blue-orange color polymorphisms: DFR-2 specificity redirects flux from the malvidin to the pelargonidin while BZ1-2 stabilizes the pelargonidin with glucose, producing the orange pelargonidin 3-glucoside. Moreover, a reduction of F3'5'H expression in orange petals also favors pelargonidin production. The climate niches for each color morph are the same between the two species for three temperature characteristics but differ for four precipitation variables.

CONCLUSIONS

The similarities in reflectance spectra, biochemistry, and ABP genes suggest that a single shift from blue-to-orange shared by both lineages is the most plausible explanation. Our evidence suggests that this persistent flower color polymorphism may represent an ancestrally polymorphic trait that has transcended speciation, yet future analyses are necessary to confidently reject the alternative hypotheses.

Engineering an Ancestral Glycosyltransferase for Biosynthesis of 2-Phenylethyl-β-d-Glucopyranoside and Salidroside

Phenylethanoid glycosides (PhGs) are naturally occurring glycosides derived from plants with various biological activities. Glycosyltransferases catalyze the production of PhGs from phenylethanols via a transglycosylation reaction. The low activity and stability of glycosyltransferase limit its industrial application. An ancestral glycosyltransferase, UGTAn85, with heat resistance, alkali resistance, and high stability was resurrected using ancestral sequence reconstruction technology. This enzyme can efficiently convert phenylethanols to PhGs. The optimal reaction temperature and pH for UGTAn85 were found to be 70 °C and pH 10.0, respectively. This study employed a combination of structure-guided rational design and co-evolution analysis to enhance its catalytic activity. Potential mutation sites were identified through computer-aided design, including homology modeling, molecular docking, Rosetta dock design, molecular dynamics simulation, and co-evolution analysis. By targeted mutagenesis, the UGTAn85 mutant Q23E/N65D exhibited a 2.2-fold increase in enzyme activity (11.85 U/mg) and elevated affinity (Km = 0.11 mM) for 2-phenylethanol compared to UGTAn85. Following a fed-batch reaction, 36.16 g/L 2-phenylethyl-β-d-glucopyranoside and 51.49 g/L salidroside could be produced within 24 h, respectively. The findings in this study provide a new perspective on enhancing the stability and activity of glycosyltransferases, as well as a potential biocatalyst for the industrial production of PhGs.

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.

Four glycosyltransferase genes are responsible for synthesis and accumulation of different flavonol glycosides in apple tissues

Flavonols are widely synthesized throughout the plant kingdom, playing essential roles in plant physiology and providing unique health benefits for humans. Their glycosylation plays significant role in improving their stability and solubility, thus their accumulation and function. However, the genes encoding the enzymes catalyze this glycosylation remain largely unknown in apple. This study utilized a combination of methods to identify genes encoding such enzymes. Initially, candidate genes were selected based on their potential to encode UDP-dependent glycosyltransferases (UGTs) and their expression patterns in response to light induction. Subsequently, through testing the in vitro enzyme activity of the proteins produced in Escherichia coli cells, four candidates were confirmed to encode a flavonol 3-O-galactosyltransferase (UGT78T6), flavonol 3-O-glucosyltransferase (UGT78S1), flavonol 3-O-xylosyltransferase/arabinosyltransferase (UGT78T5), and flavonol 3-O-rhamnosyltransferase (UGT76AE22), respectively. Further validation of these genes' functions was conducted by modulating their expression levels in stably transformed apple plants. As anticipated, a positive correlation was observed between the expression levels of these genes and the content of specific flavonol glycosides corresponding to each gene. Moreover, overexpression of a flavonol synthase gene, MdFLS, resulted in increased flavonol glycoside content in apple roots and leaves. These findings provide valuable insights for breeding programs aimed at enriching apple flesh with flavonols and for identifying flavonol 3-O-glycosyltransferases of other plant species.

Genome-wide study of UDP-glycosyltransferases gene family in Cannabis sativa

The research focused on analyzing the UGT gene family in Cannabis sativa, which plays a crucial role in the plant's metabolism and glycosylation of secondary metabolites. The study identified 125 UGTs using conserved plant secondary product glycosyltransferase (PSPG) motif amino acid sequences. These UGT genes were categorized into 17 groups (A-Q) through phylogenetic analysis, showing their distribution across 10 chromosomes in C. sativa. The expansion of the CsUGT gene family was attributed to tandem and duplication events, as suggested by gene duplication analysis. Furthermore, the study found various cis-acting regulatory elements related to phytohormones and stress responses in CsUGT promoter regions. Subcellular localization analysis revealed that CsUGT is present in the cytoplasm, chloroplast, and nucleus. The study revealed that CsUGT plays a significant role in various biological processes, cellular components, and molecular functions as highlighted by Gene Ontology analysis. Additionally, the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis showed that some CsUGTs are associated with the biosynthesis of secondary metabolites. This research provides valuable insights into the genomic organization, evolutionary history, and potential regulatory mechanisms of UGT genes in C. sativa. It lays the foundation for further exploration of their specific biological roles and potential applications in the plant's metabolism and stress responses. These findings contribute to a better understanding of the UGT gene family and its relevance to the metabolic pathways in C. sativa.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-024-04025-3.

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

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

Identification and Functional Verification of the Glycosyltransferase Gene Family Involved in Flavonoid Synthesis in Rubus chingii Hu

Glycosylation is catalyzed by UDP-glycosyltransferase (UGT) and plays an important role in enriching the diversity of flavonoids. Rubus plants contain a lot of natural flavonoid glycosides, which are important plants with a homology of medicine and food. However, information about the Rubus UGT gene family is very limited. In this study, we carried out genome-wide analysis and identified the 172, 121, 130, 121 UGT genes in R. chingii, R. corchorifolius, R. idaeus, and R. occidentalis, respectively, and divided them into 18 groups. The analysis of the protein motif and gene structure showed that there were structural and functional conservations in the same group, but there were differences among different groups. Gene replication analysis showed that raspberry and dicotyledons had a higher homology. The expansion of the UGTs gene family was mainly driven by tandem replication events, and experienced purified selection during the long evolution of the raspberry. Cis-acting element analysis showed that they were related to plant growth and development, hormone regulation, and stress response. In addition, according to a comprehensive analysis of the co-expression network constructed by transcriptome data and phylogenetic homology, RchUGT169 was identified as a flavonoid glucosyltransferase. Through the transient expression in tobacco, it was verified that RchUGT169 could catalyze the conversion of kaempferol and quercetin to the corresponding flavonoid glycosides. In conclusion, this research enriched the understanding of the diversity of UGTs in Rubus and determined that RcUGT169 can catalyze flavonoids.

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.

Genome-wide investigation of UDP-Glycosyltransferase family in Tartary buckwheat (Fagopyrum tataricum)

BACKGROUND

Tartary buckwheat (Fagopyrum tataricum) belongs to Polygonaceae family and has attracted increasing attention owing to its high nutritional value. UDP-glycosyltransferases (UGTs) glycosylate a variety of plant secondary metabolites to control many metabolic processes during plant growth and development. However, there have been no systematic reports of UGT superfamily in F. tataricum.

RESULTS

We identified 173 FtUGTs in F. tataricum based on their conserved UDPGT domain. Phylogenetic analysis of FtUGTs with 73 Arabidopsis UGTs clustered them into 21 families. FtUGTs from the same family usually had similar gene structure and motif compositions. Most of FtUGTs did not contain introns or had only one intron. Tandem repeats contributed more to FtUGTs amplification than segmental duplications. Expression analysis indicates that FtUGTs are widely expressed in various tissues and likely play important roles in plant growth and development. The gene expression analysis response to different abiotic stresses showed that some FtUGTs were involved in response to drought and cadmium stress. Our study provides useful information on the UGTs in F. tataricum, and will facilitate their further study to better understand their function.

CONCLUSIONS

Our results provide a theoretical basis for further exploration of the functional characteristics of FtUGTs and for understanding the growth, development, and metabolic model in F. tataricum.

Functional Identification of HhUGT74AG11-A Key Glycosyltransferase Involved in Biosynthesis of Oleanane-Type Saponins in Hedera helix

Hedera helix is a traditional medicinal plant. Its primary active ingredients are oleanane-type saponins, which have extensive pharmacological effects such as gastric mucosal protection, autophagy regulation actions, and antiviral properties. However, the glycosylation-modifying enzymes responsible for catalyzing oleanane-type saponin biosynthesis remain unidentified. Through transcriptome, cluster analysis, and PSPG structural domain, this study preliminarily screened four candidate UDP-glycosyltransferases (UGTs), including Unigene26859, Unigene31717, CL11391.Contig2, and CL144.Contig9. In in vitro enzymatic reactions, it has been observed that Unigene26859 (HhUGT74AG11) has the ability to facilitate the conversion of oleanolic acid, resulting in the production of oleanolic acid 28-O-glucopyranosyl ester. Moreover, HhUGT74AG11 exhibits extensive substrate hybridity and specific stereoselectivity and can transfer glycosyl donors to the C-28 site of various oleanane-type triterpenoids (hederagenin and calenduloside E) and the C-7 site of flavonoids (tectorigenin). Cluster analysis found that HhUGT74AG11 is clustered together with functionally identified genes AeUGT74AG6, CaUGT74AG2, and PgUGT74AE2, further verifying the possible reason for HhUGT74AG11 catalyzing substrate generalization. In this study, a novel glycosyltransferase, HhUGT74AG11, was characterized that plays a role in oleanane-type saponins biosynthesis in H. helix, providing a theoretical basis for the production of rare and valuable triterpenoid saponins.

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

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

Analysis of the UDP-Glucosyltransferase (UGT) Gene Family and Its Functional Involvement in Drought and Salt Stress Tolerance in Phoebe bournei

Uridine diphosphate glycosyltransferases (UDP-GTs, UGTs), which are regulated by UGT genes, play a crucial role in glycosylation. In vivo, the activity of UGT genes can affect the availability of metabolites and the rate at which they can be eliminated from the body. UGT genes can exert their regulatory effects through mechanisms such as post-transcriptional modification, substrate subtype specificity, and drug interactions. Phoebe bournei is an economically significant tree species that is endemic to southern China. Despite extensive studies on the UGT gene family in various species, a comprehensive investigation of the UGT family in P. bournei has not been reported. Therefore, we conducted a systematic analysis to identify 156 UGT genes within the entire P. bournei genome, all of which contained the PSPG box. The PbUGT family consists of 14 subfamilies, consistent with Arabidopsis thaliana. We observed varying expression levels of PbUGT genes across different tissues in P. bournei, with the following average expression hierarchy: leaf > stem xylem > stem bark > root xylem > root bark. Covariance analysis revealed stronger covariance between P. bournei and closely related species. In addition, we stressed the seedlings with 10% NaCl and 10% PEG-6000. The PbUGT genes exhibited differential expression under drought and salt stresses, with specific expression patterns observed under each stress condition. Our findings shed light on the transcriptional response of PbUGT factors to drought and salt stresses, thereby establishing a foundation for future investigations into the role of PbUGT transcription factors.

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

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

OsUGT88C3 Encodes a UDP-Glycosyltransferase Responsible for Biosynthesis of Malvidin 3-O-Galactoside in Rice

The diversity of anthocyanins is largely due to the action of glycosyltransferases, which add sugar moieties to anthocyanidins. Although a number of glycosyltransferases have been identified to glycosylate anthocyanidin in plants, the enzyme that catalyzes malvidin galactosylation remains unclear. In this study, we identified three rice varieties with different leaf color patterns, different anthocyanin accumulation patterns, and different expression patterns of anthocyanin biosynthesis genes (ABGs) to explore uridine diphosphate (UDP)-glycosyltransferases (UGTs) responsible for biosynthesis of galactosylated malvidin. Based on correlation analysis of transcriptome data, nine candidate UGT genes coexpressed with 12 ABGs were identified (r values range from 0.27 to 1.00). Further analysis showed that the expression levels of one candidate gene, OsUGT88C3, were highly correlated with the contents of malvidin 3-O-galactoside, and recombinant OsUGT88C3 catalyzed production of malvidin 3-O-galactoside using UDP-galactose and malvidin as substrates. OsUGT88C3 was closely related to UGTs with flavone and flavonol glycosylation activities in phylogeny. Its plant secondary product glycosyltransferase (PSPG) motif ended with glutamine. Haplotype analysis suggested that the malvidin galactosylation function of OsUGT88C3 was conserved among most of the rice germplasms. OsUGT88C3 was highly expressed in the leaf, pistil, and embryo, and its protein was located in the endoplasmic reticulum and nucleus. Our findings indicate that OsUGT88C3 is responsible for the biosynthesis of malvidin 3-O-galactoside in rice and provide insight into the biosynthesis of anthocyanin in plants.

Genomic insights into the evolution of flavonoid biosynthesis and O-methyltransferase and glucosyltransferase in Chrysanthemum indicum

Flavonoids are a class of secondary metabolites widely distributed in plants. Regiospecific modification by methylation and glycosylation determines flavonoid diversity. A rare flavone glycoside, diosmin (luteolin-4'-methoxyl-7-O-glucosyl-rhamnoside), occurs in Chrysanthemum indicum. How Chrysanthemum plants evolve new biosynthetic capacities remains elusive. Here, we assemble a 3.11-Gb high-quality C. indicum genome with a contig N50 value of 4.39 Mb and annotate 50,606 protein-coding genes. One (CiCOMT10) of the tandemly repeated O-methyltransferase genes undergoes neofunctionalization, preferentially transferring the methyl group to the 4'-hydroxyl group of luteolin with ortho-substituents to form diosmetin. In addition, CiUGT11 (UGT88B3) specifically glucosylates 7-OH group of diosmetin. Next, we construct a one-pot cascade biocatalyst system by combining CiCOMT10, CiUGT11, and our previously identified rhamnosyltransferase, effectively producing diosmin with over 80% conversion from luteolin. This study clarifies the role of transferases in flavonoid diversity and provides important gene elements essential for producing rare flavone.

Fusarium sporotrichioides Produces Two HT-2-α-Glucosides on Rice

Fusarium is a genus that mostly consists of plant pathogenic fungi which are able to produce a broad range of toxic secondary metabolites. In this study, we focus on a type A trichothecene-producing isolate (15-39) of Fusarium sporotrichioides from Lower Austria. We assessed the secondary metabolite profile and optimized the toxin production conditions on autoclaved rice and found that in addition to large amounts of T-2 and HT-2 toxins, this strain was able to produce HT-2-glucoside. The optimal conditions for the production of T-2 toxin, HT-2 toxin, and HT-2-glucoside on autoclaved rice were incubation at 12 °C under constant light for four weeks, darkness at 30 °C for two weeks, and constant light for three weeks at 20 °C, respectively. The HT-2-glucoside was purified, and the structure elucidation by NMR revealed a mixture of two alpha-glucosides, presumably HT-2-3-O-alpha-glucoside and HT-2-4-O-alpha-glucoside. The efforts to separate the two compounds by HPLC were unsuccessful. No hydrolysis was observed with two the alpha-glucosidases or with human salivary amylase and Saccharomyces cerevisiae maltase. We propose that the two HT-2-alpha-glucosides are not formed by a glucosyltransferase as they are in plants, but by a trans-glycosylating alpha-glucosidase expressed by the fungus on the starch-containing rice medium.

Transcriptomic Analyses Reveal Insights into the Shared Regulatory Network of Phenolic Compounds and Steviol Glycosides in Stevia rebaudiana

Stevia rebaudiana (Bertoni) is a highly valuable crop for the steviol glycoside content in its leaves, which are no-calorie sweeteners hundreds of times more potent than sucrose. The presence of health-promoting phenolic compounds, particularly flavonoids, in the leaf of S. rebaudiana adds further nutritional value to this crop. Although all these secondary metabolites are highly desirable in S. rebaudiana leaves, the genes regulating the biosynthesis of phenolic compounds and the shared gene network between the regulation of biosynthesis of steviol glycosides and phenolic compounds still need to be investigated in this species. To identify putative candidate genes involved in the synergistic regulation of steviol glycosides and phenolic compounds, four genotypes with different contents of these compounds were selected for a pairwise comparison RNA-seq analysis, yielding 1136 differentially expressed genes. Genes that highly correlate with both steviol glycosides and phenolic compound accumulation in the four genotypes of S. rebaudiana were identified using the weighted gene co-expression network analysis. The presence of UDP-glycosyltransferases 76G1, 76H1, 85C1, and 91A1, and several genes associated with the phenylpropanoid pathway, including peroxidase, caffeoyl-CoA O-methyltransferase, and malonyl-coenzyme A:anthocyanin 3-O-glucoside-6″-O-malonyltransferase, along with 21 transcription factors like SCL3, WRK11, and MYB111, implied an extensive and synergistic regulatory network involved in enhancing the production of such compounds in S. rebaudiana leaves. In conclusion, this work identified a variety of putative candidate genes involved in the biosynthesis and regulation of particular steviol glycosides and phenolic compounds that will be useful in gene editing strategies for increasing and steering the production of such compounds in S. rebaudiana as well as in other species.

Selective synthesis of rebaudioside M2 through structure-guided engineering of glycosyltransferase UGT94D1

Rebaudioside M2 (Reb M2), a novel steviol glycoside derivative, has limited industrial applications due to its low synthetic yield and selectivity. Herein, we identify UGT94D1 as a selective glycosyltransferase for rebaudioside D (Reb D), leading to the production of a mono β-1,6-glycosylated derivative, Reb M2. A variant UGT94D1-F119I/D188P was developed through protein engineering. This mutant exhibited a 6.33-fold improvement in catalytic efficiency, and produced Reb M2 with 92% yield. Moreover, molecular dynamics simulations demonstrated that UGT94D1-F119I/D188P exhibited a shorter distance between the nucleophilic oxygen (OH6) of the substrate Reb D and uridine diphosphate glucose, along with an increased Ophosphate-C1-Oacceptor angle, thus improving the catalytic activity of the enzyme. Therefore, this study provides an efficient method for the selective synthesis of Reb M2 and paves the way for its applications in various fields.

Systematic analysis of the UDP-glucosyltransferase family: discovery of a member involved in rutin biosynthesis in Solanum melongena

Eggplant (Solanum melongena) is an economically important crop and rich in various nutrients, among which rutin that has positive effects on human health is found in eggplant. Glycosylation mediated by UDP-glycosyltransferases (UGTs) is a key step in rutin biosynthesis. However, the UGT gene has not been reported in eggplant to date. Herein, 195 putative UGT genes were identified in eggplant by genome-wide analysis, and they were divided into 17 subgroups (Group A-P and Group R) according to the phylogenetic evolutionary tree. The members of Groups A, B, D, E and L were related to flavonol biosynthesis, and rutin was the typical flavonol. The expression profile showed that the transcriptional levels of SmUGT genes in Clusters 7-10 were closely related to those of rutin biosynthetic pathway genes. Notably, SmUGT89B2 was classified into Cluster 7 and Group B; its expression was consistent with rutin accumulation in different tissues and different leaf stages of eggplant. SmUGT89B2 was located in the nucleus and cell membrane. Virus-induced gene silencing (VIGS) and transient overexpression assays showed that SmUGT89B2 can promote rutin accumulation in eggplant. These findings provide new insights into the UGT genes in eggplant, indicating that SmUGT89B2 is likely to encode the final enzyme in rutin biosynthesis.

Transcriptome analysis provides insights into coumarin biosynthesis in the medicinal plant Angelica dahurica cv. Yubaizhi

Angelica dahurica roots have a long history of use in traditional Chinese medicine due to their high coumarin content. To address the increasing demand for these roots, a synthetic biology approach has been proposed. Nevertheless, our comprehension of coumarin biosynthesis and its regulation remains limited. In this study, we utilized Hiseq2500 sequencing to analyze the transcriptomes of A. dahurica at different growth stages while concurrently quantifying coumarin content. Differentially expressed gene (DEG) analysis was employed to identify key genes involved in coumarin and terpenoid backbone biosynthesis. Weighted gene co-expression network analysis (WGCNA) was applied to identify gene modules strongly associated with coumarin content, elucidating the regulatory relationships between transcription factors (TFs) and pathway genes. Furthermore, KEGG enrichment analysis was used to explore essential pathways governing coumarin biosynthesis, with the identification of hub genes. Our results indicated that total coumarin content was highest in the roots, followed by leaves and stems, across all three developmental stages. Transcriptome analysis identified a total of 92,478 genes, among which 215 and 30 genes were implicated in coumarin and terpenoid backbone biosynthesis, respectively. Within the 73 identified gene modules by WGCNA, three modules-namely aquamarine1 (comprising two OMTs, one CSE, one AACT, one HDS, two PSs, one 2OGO, four UGTs, and seven CYP450s), darkmagenta (containing one UGT and one HDR), and navajowhite2 (consisting of one HCT, three UGTs, one CYP71A25, one OMT, one CSE, one HDS, and one PT)-were strongly associated with imperatorin, oxypeucedanin, and isoimperatorin content, respectively. KEGG enrichment analysis highlighted significant enrichment of cytochrome P450, transporter, and ubiquitin system pathways. Moreover, TF-gene regulatory analysis unveiled the complexity of coumarin biosynthesis, with 17 TF families regulating 17 genes in the aquamarine1 module, 8 TF families regulating 2 genes in the darkmagenta module, and 8 TF families regulating 7 genes in the navajowhite2 module. These comprehensive findings provide valuable insights into coumarin biosynthesis in A. dahurica, facilitating future research and potential applications in traditional Chinese medicine and synthetic biology strategies.

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

BACKGROUND

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

RESULTS

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

CONCLUSIONS

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

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

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

Genome-Wide Analysis of Family-1 UDP-Glycosyltransferases in Potato (Solanum tuberosum L.): Identification, Phylogenetic Analysis and Determination of Response to Osmotic Stress

Family-1 UDP-glycosyltransferases (UGTs) are the most common and functional glycosyltransferases in the plant world. UGT is closely related to plant growth and the response to abiotic stress. However, despite systematic research, our understanding of potato UGT genes is still unclear. In this study, we identified 174 potato UGT proteins based on their conserved plant secondary product glycosyltransferase (PSPG) motifs. Phylogenetic analyses were used to compare these proteins with Arabidopsis UGTs and other plant UGTs, and it was found that they could be clustered into 18 distinct groups. Patterns of intron gain/loss and intron phases within potato UGTs revealed highly conserved intron insertion events. The promoter cis-elements of these 174 UGT genes were systematically investigated. The promoter regions of these UGT genes are known to contain various classes of cis-acting compounds. These include elements that are light-responsive, phytohormone-responsive, and stress-responsive. Transcriptome data analysis established that 25, 10, 6, and 4 of these 174 UGT genes were specifically expressed in leaves, roots, stolons, and young tubers, respectively. The mannitol-treated transcriptomic data showed thirty-eight UGT genes were significantly upregulated. The quantitative real-time PCR results showed that the four genes were all responsive to osmotic stress under a 10% PEG6000 treatment. The results of our study provide a basis for clarifying the molecular mechanism of potato osmotic stress resistance and better understanding its function in the future.

Characterization of Glycosyltransferase Family 1 (GT1) and Their Potential Roles in Anthocyanin Biosynthesis in Maize

Glycosyltransferase family 1 (GT1) is a large group of proteins that play critical roles in secondary metabolite biosynthesis in plants. However, the GT1 family is not well studied in maize. In this study, 107 GT1 unigenes were identified in the maize reference genome and classified into 16 groups according to their phylogenetic relationship. GT1s are unevenly distributed across all ten maize chromosomes, occurring as gene clusters in some chromosomes. Collinearity analysis revealed that gene duplication events, whole-genome or segmental duplication, and tandem duplication occurred at a similar frequency, indicating that both types of gene duplication play notable roles in the expansion of the GT1 gene family. Expression analysis showed GT1s expressing in all tissues with specific expression patterns of each GT1, suggesting that they might participate in multiple biological processes during the whole growth and development stages. Furthermore, 16 GT1s were identified to have similar expression patterns to those of anthocyanidin synthase (ANS), the critical enzyme in anthocyanin biosynthesis. Molecular docking was carried out to examine the affinity of GT1s with substrates in anthocyanin biosynthesis. This study provides valuable information on the GT1s of maize and will promote the development of research on their biological functions in the biosynthesis of other secondary metabolites.

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

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