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

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.

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.

Transcriptomic and proteomic responses of sweetpotato whitefly, Bemisia tabaci, to thiamethoxam

BACKGROUND

The sweetpotato whitefly, Bemisia tabaci (Hemiptera: Aleyrodidae), is one of the most widely distributed agricultural pests. Although it has developed resistance to many registered insecticides including the neonicotinoid insecticide thiamethoxam, the mechanisms that regulate the resistance are poorly understood. To understand the molecular basis of thiamethoxam resistance, "omics" analyses were carried out to examine differences between resistant and susceptible B. tabaci at both transcriptional and translational levels.

RESULTS

A total of 1,338 mRNAs and 52 proteins were differentially expressed between resistant and susceptible B. tabaci. Among them, 11 transcripts had concurrent transcription and translation profiles. KEGG analysis mapped 318 and 35 differentially expressed genes and proteins, respectively, to 160 and 59 pathways (p<0.05). Thiamethoxam treatment activated metabolic pathways (e.g., drug metabolism), in which 118 transcripts were putatively linked to insecticide resistance, including up-regulated glutathione-S-transferase, UDP glucuronosyltransferase, glucosyl/glucuronosyl transferase, and cytochrome P450. Gene Ontology analysis placed these genes and proteins into protein complex, metabolic process, cellular process, signaling, and response to stimulus categories. Quantitative real-time PCR analysis validated "omics" response, and suggested a highly overexpressed P450, CYP6CX1, as a candidate molecular basis for the mechanistic study of thiamethoxam resistance in whiteflies. Finally, enzymatic activity assays showed elevated detoxification activities in the resistant B. tabaci.

CONCLUSIONS

This study demonstrates the applicability of high-throughput omics tools for identifying molecular candidates related to thiamethoxam resistance in an agricultural important insect pest. In addition, transcriptomic and proteomic analyses provide a solid foundation for future functional investigations into the complex molecular mechanisms governing the neonicotinoid resistance in whiteflies.

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.

Purification and characterization of a UDP-glucosyltransferase produced by Legionella pneumophila

Legionella pneumophila is the agent of Legionnaires' disease. It invades and replicates within eukaryotic cells, including aquatic protozoans, mammalian macrophages, and epithelial cells. The molecular mechanisms of the Legionella interaction with target cells are not fully defined. In an attempt to discover novel virulence factors of L. pneumophila, we searched for bacterial enzymes with transferase activity. Upon screening ultrasonic extracts of virulent legionellae, we identified a uridine diphospho (UDP)-glucosyltransferase activity, which was capable of modifying a 45-kDa substrate in host cells. An approximately 60-kDa UDP-glucosyltransferase was purified from L. pneumophila and subjected to microsequencing. An N-terminal amino acid sequence, as well as the sequence of an internal peptide, allowed us to identify the gene for the enzyme within the unfinished L. pneumophila genome database. The intact gene was cloned and expressed in Escherichia coli, and the recombinant protein was purified and confirmed to possess an enzymatic activity similar to that of the native UDP-glucosyltransferase. We designated this gene ugt (UDP-glucosyltransferase). The Legionella enzyme did not exhibit significant homology with any known protein, suggesting that it is novel in structure and, perhaps, in function. Based on PCR data, an enzyme assay, and an immunoblot analysis, the glucosyltransferase appeared to be conserved in L. pneumophila strains but was absent from the other Legionella species. This study represents the first identification of a UDP-glucosyltransferase in an intracellular parasite, and therefore modification of a eukaryotic target(s) by this enzyme may influence host cell function and promote L. pneumophila proliferation.

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.

Preferential expression of biotransformation enzymes in the olfactory organs of Drosophila melanogaster, the antennae

Biotransformation enzymes have been found in the olfactory epithelium of vertebrates. We now show that in Drosophila melanogaster, a UDP-glycosyltransferase (UGT), as well as a short chain dehydrogenase/reductase and a cytochrome P450 are expressed specifically or preferentially in the olfactory organs, the antennae. The evolutionarily conserved expression of biotransformation enzymes in olfactory organs suggests that they play an important role in olfaction. In addition, we describe five Drosophila UGTs belonging to two families. All five UGTs contain a putative transmembrane domain at their C terminus as is the case for vertebrate UGTs where it is required for enzymatic activity. The primary sequence of the C terminus, including part of the transmembrane domain, differs between the two families but is highly conserved not only within each Drosophila family, but also between the members of one of the Drosophila families and vertebrate UGTs. The partial overlap of the conserved primary sequence with the transmembrane domain suggests that this part of the protein is involved in specific interactions occurring at the membrane surface. The presence of different C termini in the two Drosophila families suggests that they interact with different targets, one of which is conserved between Drosophila and vertebrates.