UDP-glucosyltransferase activity toward exogenous substrates in Drosophila melanogaster

UGT201H1 overexpression confers cyflumetofen resistance in Tetranychus cinnabarinus (Boisduval)

BACKGROUND

Tetranychus cinnabarinus is one of the most common polyphagous arthropod herbivores, and is primarily controlled by the application of acaricides. The heavy use of acaricides has led to high levels of resistance to acaricides such as cyflumetofen, which poses a threat to global resistance management programs. Cyflumetofen resistance is caused by an increase in metabolic detoxification; however, the role of uridine diphosphate (UDP)-glycosyltransferase (UGT) genes in cyflumetofen resistance remains to be determined.

RESULTS

Synergist 5-nitrouracil (5-Nul) significantly enhanced cyflumetofen toxicity in T. cinnabarinus, which indicated that UGTs are involved in the development of cyflumetofen resistance. Transcriptomic analysis and quantitative (q)PCR assays demonstrated that the UGT genes, especially UGT201H1, were highly expressed in the YN-CyR strain, compared to those of the YN-S strain. The RNA interference (RNAi)-mediated knockdown of UGT201H1 expression diminished the levels of cyflumetofen resistance in YN-CyR mites. The findings additionally revealed that the recombinant UGT201H1 protein plays a role in metabolizing cyflumetofen. Our results also suggested that the aromatic hydrocarbon receptor (AhR) probably regulates the overexpression of the UGT201H1 detoxification gene.

CONCLUSION

UGT201H1 is involved in cyflumetofen resistance, and AhR may regulates the overexpression of UGT201H1. These findings provide deeper insights into the molecular mechanisms underlying UGT-mediated metabolic resistance to chemical insecticides. © 2024 Society of Chemical Industry.

UGT440A1 Is Associated With Motility, Reproduction, and Pathogenicity of the Plant-Parasitic Nematode Bursaphelenchus xylophilus

Pine wilt disease (PWD) caused by Bursaphelenchus xylophilus is considered a major threat to pine forests worldwide. Uridine diphosphate (UDP)-glycosyltransferases (UGTs) catalyze the conjugation of small lipophilic compounds with sugars and play crucial roles in the detoxification and homeostatic processes in all living organisms. We investigated the molecular characteristics and biological functions of the gene UGT440A1 that encodes UGTs in B. xylophilus. The in situ hybridization results indicated that UGT440A1 is expressed in all developmental stages of B. xylophilus, particularly in the head, intestine, and hypodermis of the second-stage of juveniles (J2), third-stage of juveniles (J3) and fourth-stage of juveniles (J4) females and in almost the whole body of J4 males and adults. Recombinant UGT440A1 was observed mainly in the inclusion bodies, and the enzyme activity assay revealed that UGT440A1 could catalyze the glycosylation reaction of two types of flavonols (kaempferol and quercetin). RNA interference (RNAi) of UGT440A1 suppressed motility, feeding, and reproduction of B. xylophilus. Furthermore, UGT440A1 knockdown caused a delay in the development of PWD symptoms in the pine seedlings inoculated with the nematodes. These results suggest that UGT440A1 is involved in the pathogenic process of B. xylophilus and the information may facilitate a better understanding of the molecular mechanism of PWD.

Glycosyltransferases: the multifaceted enzymatic regulator in insects

Glycosyltransferases (GTs) catalyse the reaction of glyco-conjugation of various biomolecules by transferring the saccharide moieties from an activated nucleotide sugar to nucleophilic glycosyl acceptor. In insects, GTs show diverse temporal and site-specific expression patterns and thus play significant roles in forming the complex biomolecular structures that are necessary for insect survival, growth and development. Several insects exhibit GT-mediated detoxification as a key defence strategy against plant allelochemicals and xenobiotic compounds, as well as a mechanism for pesticide cross-resistance. Also, these enzymes act as crucial effectors and modulators in various developmental processes of insects such as eye development, UV shielding, cuticle formation, epithelial development and other specialized functions. Furthermore, many of the known insect GTs have been shown to play a fundamental role in other physiological processes like body pigmentation, cuticular tanning, chemosensation and stress response. This review provides a detailed overview of the multifaceted functionality of insect GTs and summarizes numerous case studies associated with it.

The UDP-Glycosyltransferase Family in Drosophila melanogaster: Nomenclature Update, Gene Expression and Phylogenetic Analysis

UDP-glycosyltransferases (UGTs) are important conjugation enzymes found in all kingdoms of life, catalyzing a sugar conjugation with small lipophilic compounds and playing a crucial role in detoxification and homeostasis. The UGT gene family is defined by a signature motif in the C-terminal domain where the uridine diphosphate (UDP)-sugar donor binds. UGTs have been identified in a number of insect genomes over the last decade and much progress has been achieved in characterizing their expression patterns and molecular functions. Here, we present an update of the complete repertoire of UGT genes in Drosophila melanogaster and provide a brief overview of the latest research in this model insect. A total of 35 UGT genes are found in the D. melanogaster genome, localized to chromosomes 2 and 3 with a high degree of gene duplications on the chromosome arm 3R. All D. melanogaster UGT genes have now been named in FlyBase according to the unified UGT nomenclature guidelines. A phylogenetic analysis of UGT genes shows lineage-specific gene duplications. Analysis of anatomical and induced gene expression patterns demonstrate that some UGT genes are differentially expressed in various tissues or after environmental treatments. Extended searches of UGT orthologs from 18 additional Drosophila species reveal a diversity of UGT gene numbers and composition. The roles of Drosophila UGTs identified to date are briefly reviewed, and include xenobiotic metabolism, nicotine resistance, olfaction, cold tolerance, sclerotization, pigmentation, and immunity. Together, the updated genomic information and research overview provided herein will aid further research in this developing field.

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.

Jinggangmycin-Induced UDP-Glycosyltransferase 1-2-Like Is a Positive Modulator of Fecundity and Population Growth in Nilaparvata lugens (Stål) (Hemiptera: Delphacidae)

The antibiotic jinggangmycin (JGM) is broadly applied in Chinese rice producing regions to control rice blight, a fungal disease. Aside from protecting rice plants from the disease, JGM leads to the unexpected action of stimulating brown planthopper (BPH; Nilaparvata lugens; Hemiptera: Delphacidae) reproduction to the extent it can influence population sizes. The JGM-induced BPH population growth has potential for severe agricultural problems and we are working to understand and mitigate the mechanisms of the enhanced reproduction. UDP-glucuronosyltransferases (UGTs) are multifunctional detoxification enzymes responsible for biotransformation of diverse lipophilic compounds. The biological significance of this enzyme family in insect fecundity is not fully understood, however, upregulated UGT12 in JGM-treated BPH, may influence fecundity through metabolism of developmental hormones. This idea prompted our hypothesis that NlUGT12 is a positive modulator of BPH reproductive biology. JGM treatment led to significant increases in accumulations of mRNA encoding NlUGT12, numbers of eggs laid, oviposition period, juvenile hormone III titers, and fat body, and ovarian protein contents. dsUGT12 treatment suppressed NlUGT12 expression and reversed JGM-enhanced effects, resulting in under-developed ovaries and reduced expression of juvenile hormone acid methyltransferase and the JH receptor, methoprene tolerant. Application of the JH analog, methoprene, on dsUGT12 treated-females partially reversed the dsUTG12 influence on vitellogenin synthesis and on NlUGT12 expression. These results represent an important support for our hypothesis.

Chemical defense balanced by sequestration and de novo biosynthesis in a lepidopteran specialist

The evolution of sequestration (uptake and accumulation) relative to de novo biosynthesis of chemical defense compounds is poorly understood, as is the interplay between these two strategies. The Burnet moth Zygaena filipendulae (Lepidoptera) and its food-plant Lotus corniculatus (Fabaceae) poses an exemplary case study of these questions, as Z. filipendulae belongs to the only insect family known to both de novo biosynthesize and sequester the same defense compounds directly from its food-plant. Z. filipendulae and L. corniculatus both contain the two cyanogenic glucosides linamarin and lotaustralin, which are defense compounds that can be hydrolyzed to liberate toxic hydrogen cyanide. The overall amounts and ratios of linamarin and lotaustralin in Z. filipendulae are tightly regulated, and only to a low extent reflect the ratio in the ingested food-plant. We demonstrate that Z. filipendulae adjusts the de novo biosynthesis of CNglcs by regulation at both the transcriptional and protein level depending on food plant composition. Ultimately this ensures that the larva saves energy and nitrogen while maintaining an effective defense system to fend off predators. By using in situ PCR and immunolocalization, the biosynthetic pathway was resolved to the larval fat body and integument, which infers rapid replenishment of defense compounds following an encounter with a predator. Our study supports the hypothesis that de novo biosynthesis of CNglcs in Z. filipendulae preceded the ability to sequester, and facilitated a food-plant switch to cyanogenic plants, after which sequestration could evolve. Preservation of de novo biosynthesis allows fine-tuning of the amount and composition of CNglcs in Z. filipendulae.

Flavonoids from the cocoon of Rondotia menciana

Two flavonol glycosides along with four known flavonoids were isolated from the cocoon of the mulberry white caterpillar, Rondotia menciana (Lepidoptera: Bombycidae: Bombycinae), a closely related species of the domesticated silkworm Bombyx mori, both of which feed on leaves of mulberry (Morus alba). The two glycosides were characterized as quercetin 3-O-β-d-galactopyranosyl-(1→3)-β-d-galactopyranoside and kaempferol 3-O-β-d-galactopyranosyl-(1→3)-β-d-galactopyranoside, based on spectroscopic data and chemical evidence. The flavonol galactosides found in the cocoon were not present in the host plant, nor in the cocoon of the silkworm, B. mori. Notably, flavonol glucosides, which are the main constituents of cocoon flavonoids in B. mori mori, were not found in the R. menciana cocoon. The present result strongly suggests that R. menciana is quite unique in that they predominantly use an UDP-galactosyltransferase for conjugation of dietary flavonoids, whereas UDP-glucosyltransferases are generally used for conjugation of plant phenolics and xenobiotics in other insects.

Comparative analysis of the UDP-glycosyltransferase multigene family in insects

UDP-glycosyltransferases (UGT) catalyze the conjugation of a range of diverse small lipophilic compounds with sugars to produce glycosides, playing an important role in the detoxification of xenobiotics and in the regulation of endobiotics in insects. Recent progress in genome sequencing has enabled an assessment of the extent of the UGT multigene family in insects. Here we report over 310 putative UGT genes identified from genomic databases of eight different insect species together with a transcript database from the lepidopteran Helicoverpa armigera. Phylogenetic analysis of the insect UGTs showed Order-specific gene diversification and inter-species conservation of this multigene family. Only one family (UGT50) is found in all insect species surveyed (except the pea aphid) and may be homologous to mammalian UGT8. Three families (UGT31, UGT32, and UGT305) related to Lepidopteran UGTs are unique to baculoviruses. A lepidopteran sub-tree constructed with 40 H. armigera UGTs and 44 Bombyx mori UGTs revealed that lineage-specific expansions of some families in both species appear to be driven by diversification in the N-terminal substrate binding domain, increasing the range of compounds that could be detoxified or regulated by glycosylation. By comparison of the deduced protein sequences, several important domains were predicted, including the N-terminal signal peptide, UGT signature motif, and C-terminal transmembrane domain. Furthermore, several conserved residues putatively involved in sugar donor binding and catalytic mechanism were also identified by comparison with human UGTs. Many UGTs were expressed in fat body, midgut, and Malpighian tubules, consistent with functions in detoxification, and some were expressed in antennae, suggesting a role in pheromone deactivation. Transcript variants derived from alternative splicing, exon skipping, or intron retention produced additional UGT diversity. These findings from this comparative study of two lepidopteran UGTs as well as other insects reveal a diversity comparable to this gene family in vertebrates, plants and fungi and show the magnitude of the task ahead, to determine biochemical function and physiological relevance of each UGT enzyme.

The UDP-glucosyltransferase multigene family in Bombyx mori

Background

Glucosidation plays a major role in the inactivation and excretion of a great variety of both endogenous and exogenous compounds. A class of UDP-glycosyltransferases (UGTs) is involved in this process. Insect UGTs play important roles in several processes, including detoxication of substrates such as plant allelochemicals, cuticle formation, pigmentation, and olfaction. Identification and characterization of Bombyx mori UGT genes could provide valuable basic information for this important family and explain the detoxication mechanism and other processes in insects.

Results

Taking advantage of the newly assembled genome sequence, we performed a genome-wide analysis of the candidate UGT family in the silkworm, B. mori. Based on UGT signature and their similarity to UGT homologs from other organisms, we identified 42 putative silkworm UGT genes. Most of them are clustered on the silkworm chromosomes, with two major clusters on chromosomes 7 and 28, respectively. The phylogenetic analysis of these identified 42 UGT protein sequences revealed five major groups. A comparison of the silkworm UGTs with homologs from other sequenced insect genomes indicated that some UGTs are silkworm-specific genes. The expression patterns of these candidate genes were investigated with known expressed sequence tags (ESTs), microarray data, and RT-PCR method. In total, 36 genes were expressed in tissues examined and showed different patterns of expression profile, indicating that these UGT genes might have different functions.

Conclusion

B. mori possesses a largest insect UGT gene family characterized to date, including 42 genes. Phylogenetic analysis, genomic organization and expression profiles provide an overview for the silkworm UGTs and facilitate their functional studies in future.

Regioselective formation of quercetin 5-O-glucoside from orally administered quercetin in the silkworm, Bombyx mori

The cocoons of some races of the silkworm, Bombyx mori, have been shown to contain 5-O-glucosylated flavonoids, which do not occur naturally in the leaves of their host plant, mulberry (Morus alba). Thus, dietary flavonoids could be biotransformed in this insect. In this study, we found that after feeding silkworms a diet rich in the flavonol quercetin, quercetin 5-O-glucoside was the predominant metabolite in the midgut tissue, while quercetin 5,4'-di-O-glucoside was the major constituent in the hemolymph and silk glands. UDP-glucosyltransferase (UGT) in the midgut could transfer glucose to each of the hydroxyl groups of quercetin, with a preference for formation of 5-O-glucoside, while quercetin 5,4'-di-O-glucoside was predominantly produced if the enzyme extracts of either the fat body or silk glands were incubated with quercetin 5-O-glucoside and UDP-glucose. These results suggest that dietary quercetin was glucosylated at the 5-O position in the midgut as the first-pass metabolite of quercetin after oral absorption, then glucosylated at the 4'-O position in the fat body or silk glands. The 5-O-glucosylated flavonoids retained biological activity in the insect, since the total free radical scavenging capacity of several tissues increased after oral administration of quercetin.

Functional and phylogenetic analyses of a putative Drosophila melanogaster UDP-glycosyltransferase gene

Glucosidation plays a major role in the inactivation and excretion of a great variety of both endogenous and exogenous compounds. The recent determination of the complete genome sequence of Drosophila melanogaster has revealed the presence of over 30 putative UDP-glucosyltransferase (UGT) genes in this organism. We report here the molecular cloning and functional characterisation of one of these genes, named DmUgt37a1. The predicted protein comprises 525 amino acids and has about 30% overall amino acid identity with vertebrate members of the UGT family. The phylogenetic relationships of DmUgt37a1 with other members of the UGT family from D. melanogaster are discussed. DmUgt37a1 was expressed in lepidopteran insect cells and the ability of the enzyme to conjugate 38 potential substrates belonging to diverse chemical groups was assessed using UDP-glucose as sugar-donor. However, no activity was detected with any compound under the conditions used and thus, the substrate specificity of the enzyme remains unknown.

Characterization of a novel silkworm (Bombyx mori) phenol UDP-glucosyltransferase

Sugar conjugation is a major pathway for the inactivation and excretion of both endogenous and exogenous compounds. We report here the molecular cloning and functional characterization of a phenol UDP-glucosyltransferase (UGT) from the silkworm, Bombyx mori, which was named BmUGT1. The complete cDNA clone is 1.6 kb, and the gene is expressed in several tissues of fifth-instar larvae, including fat body, midgut, integument, testis, silk gland and haemocytes. The predicted protein comprises 520 amino acids and has approximately 30% overall amino-acid identity with other members of the UGT family. The most conserved region of the protein is the C-terminal half, which has been implicated in binding the UDP-sugar. BmUGT1 was expressed in insect cells using the baculovirus expression system, and a range of compounds belonging to diverse chemical groups were assessed as potential substrates for the enzyme. The expressed enzyme had a wide substrate specificity, showing activity with flavonoids, coumarins, terpenoids and simple phenols. These results support a role for the enzyme in detoxication processes, such as minimizing the harmful effects of ingested plant allelochemicals. This work represents the first instance where an insect ugt gene has been associated with a specific enzyme activity.

Molecular cloning and heterologous expression of novel glucosyltransferases from tobacco cultured cells that have broad substrate specificity and are induced by salicylic acid and auxin

Scopoletin is one of the phytoalexins in tobacco. Cells of the T-13 cell line (Nicotiana tabacum L. Bright Yellow) accumulate a large amount of scopoletin, also known as 7-hydroxy-6-methoxycoumarin, as a glucoconjugate, scopolin, in vacuoles. We report here the molecular cloning of glucosyltransferases that can catalyze the glucosylation of many kinds of secondary metabolites including scopoletin. Two cDNAs encoding glucosyltransferase (NtGT1a and NtGT1b) were isolated from a cDNA library derived from the tobacco T-13 cell line by screening with heterologous cDNAs as a probe. The deduced amino-acid sequences of NtGT1a and NtGT1b exhibited 92% identity with each other, approximately 20-50% identities with other reported glucosyltransferases. Heterologous expression of these genes in Escherichia coli showed that the recombinant enzymes had glucosylation activity against both flavonoids and coumarins. They also strongly reacted with 2-naphthol as a substrate. These recombinant enzymes can utilize UDP-glucose as the sugar donor, but they can also utilize UDP-xylose as a weak donor. RNA blot analysis showed that these genes are induced by salicylic acid and auxin, but the time course of the expression was different. This result is similar to the changes in scopoletin glucosylation activity in these tobacco cells after addition of these plant growth regulators. These results might suggest that one of the roles of the products of these genes is scopoletin glucosylation, in response to salicylic acid and/or auxin, together with the other glucosyltransferases in tobacco cells.

Separation by FPLC chromatofocusing of UDP-glucosyltransferases from three developmental stages of Drosophila melanogaster

Variation of UDP-glucosyltransferase activity, during Drosophila melanogaster development, was analyzed. The endogenous metabolite xanthurenic acid and the xenobiotic compounds 1-naphthol and 2-naphthol were used as substrates. Developmentally regulated differences were observed for the three substrates, suggesting the presence of UDP-glucosyltransferase isoenzymes. This was further confirmed by FPLC chromatofocusing on a Mono P column: seven peaks of UDP-glucosyltransferase activity (pHs: > or = 6.3, 5.8, 5.5, 4.9, 4.5, 4.2, < or = 4.0) with either single or overlapping substrate specificity were detected. A single xanthurenic acid:UDP-glucosyltransferase activity (pl 5.8) was found throughout development. In contrast, a gradual increase in the number of 2-napthol:UDP-glucosyltransferase-isoenzymes (pl from 6.3 to 4.0) was observed during development, whereas no isoenzymes specific for 1-naphthol were resolved. Based on the distribution and substrate specificity of the eluted peaks in the three developmental stages analyzed, the presence of seven or possibly eight UDP-glucosyltransferase isoenzymes is proposed.

High-performance liquid chromatography-based assays of enzyme activities

Interest in using HPLC to assay enzymatic reactions continues to grow as evidenced by the more than 100 papers published during the early 1990s. HPLC can be used for any enzymatic assay that requires separation of substrates and products before quantifying the extent of the reaction. The popularity of HPLC-based assays is due to several reasons: (1) HPLC offers unsurpassed precision, specificity, sensitivity, and reproducibility. (2) Powerful microcomputers and user-friendly software automate the running of samples and collection and processing of data. (3) Current columns, especially C18 packings, separate a very wide variety of samples, and (4) A variety of on-line detectors provide a means to detect virtually any compound. This review surveys recent papers on the development of HPLC-based assays for enzymes that degrade or otherwise modify macromolecules. Methods for assaying enzymes involved in metabolic pathways are also reviewed. Work by the authors in developing HPLC-based assays for mitochondrial enzymes that use GTP/GDP and other nucleotides that cannot be or are not easily assayed by enzyme-coupled assays is discussed. These enzymes include nucleoside diphosphate kinase, succinate thiokinase, and GTP-AMP phosphotransferase. The assays are suitable for determining the submitochondrial compartmentation of enzyme activities. Finally, current and anticipated trends in HPLC technology, including new column packings and the trend toward smaller columns that give faster separations, are reviewed in relation to enzyme assays.