Identification and expression profiles of fifteen delta-class glutathione S-transferase genes from a stored-product pest, Liposcelis entomophila (Enderlein) (Psocoptera: Liposcelididae)

Overexpression of an Integument Esterase Gene LbEST-inte4 Infers the Malathion Detoxification in Liposcelis bostrychophila (Psocoptera: Liposcelididae)

Liposcelis bostrychophila, commonly known as booklouse, is an important stored-product pest worldwide. Studies have demonstrated that booklices have developed resistance to several insecticides. In this study, an integument esterase gene, LbEST-inte4, with upregulated expression, was characterized in L. bostrychophila. Knockdown of LbEST-inte4 resulted in a substantial increase in the booklice susceptibility to malathion. Overexpression of LbEST-inte4 in Drosophila melanogaster significantly enhanced its malathion tolerance. Molecular modeling and docking analysis suggested potential interactions between LbEST-inte4 and malathion. When overexpressed LbEST-inte4 in Sf9 cells, a notable elevation in esterase activity and malathion tolerance was observed. HPLC analysis indicated that the LbEST-inte4 enzyme could effectively degrade malathion. Taken together, the upregulated LbEST-inte4 appears to contribute to malathion tolerance in L. bostrychophila by facilitating the depletion of malathion. This study elucidates the molecular mechanism underlying malathion detoxification and provides the foundations for the development of effective prevention and control measures against psocids.

Characterization of three glutathione S-transferases potentially associated with adaptation of the wheat blossom midge Sitodiplosis mosellana to host plant defense

BACKGROUND

Insect glutathione S-transferases (GSTs), a multifunctional protein family, play a crucial role in detoxification of plant defensive compounds. However, they have been rarely investigated in Sitodiplosis mosellana, a destructive pest of wheat worldwide. In this study, we characterized for the first time a delta (SmGSTd1) and two epsilon GST genes (SmGSTe1 and SmGSTe2) and analyzed their expression patterns and functions associated with adaptation to host plant defense in this species.

RESULTS

Expression of these SmGST genes greatly increased in S. mosellana larvae feeding on resistant wheat varieties Kenong1006, Shanmai139 and Jinmai47 which contain higher tannin and ferulic acid, the major defensive compounds of wheat against this pest, compared with those feeding on susceptible varieties Xinong822, Xinong88 and Xiaoyan22. Their expression was also tissue-specific, most predominant in larval midgut. Recombinant SmGSTs expressed in Escherichia coli could catalyze the conjugation of 1-chloro-2,4-dinitrobenzene, with activity peak at pH around 7.0 and temperature between 30 and 40 °C. Notably, they could metabolize tannin and ferulic acid, with the strongest metabolic ability by SmGSTe2 against two compounds, followed by SmGSTd1 on tannin, and SmGSTe1 on ferulic acid.

CONCLUSION

The results suggest that these SmGSTs are important in metabolizing wheat defensive chemicals during feeding, which may be related to host plant adaptation of S. mosellana. Our study has provided information for future investigation and development of strategies such as host-induced gene silencing of insect-detoxifying genes for managing pest adaptation. © 2023 Society of Chemical Industry.

Identification and Functional Analysis of an Epsilon Class Glutathione S-Transferase Gene Associated with α-Pinene Adaptation in Monochamus alternatus

Alpha-pinene is one of the main defensive components in conifers. Monochamus alternatus (Coleoptera: Cerambycidae), a wood borer feeding on Pinaceae plants, relies on its detoxifying enzymes to resist the defensive terpenoids. Here, we assayed the peroxide level and GST activity of M. alternatus larvae treated with different concentrations of α-pinene. Meanwhile, a gst gene (MaGSTe3) was isolated and analyzed. We determined its expression level and verified its function. The results showed that α-pinene treatment led to membrane lipid peroxidation and thus increased the GST activity. Expression of MaGSTe3 was significantly upregulated in guts following exposure to α-pinene, which has a similar pattern with the malonaldehyde level. In vitro expression and disk diffusion assay showed that the MaGSTe3 protein had high antioxidant capacity. However, RNAi treatment of MaGSTe3 did not reduce the hydrogen peroxide and malonaldehyde levels, while GST activity was significantly reduced. These results suggested MaGSTe3 takes part in α-pinene adaptation, but it does not play a great role in the resistance of M. alternatus larvae to α-pinene.

Glutathione S-Transferase May Contribute to the Detoxification of (S)-(-)-Palasonin in Plutella xylostella (L.) via Direct Metabolism

The control of P. xylostella primarily involves chemical insecticides, but overuse has brought about many negative effects. Our previous study reported that (S)-(-)-palasonin (PLN) is a plant-derived active substance with significant insecticidal activity against P. xylostella. However, we noticed a possible cross-resistance between (S)-(-)-palasonin and other insecticides which may be related to metabolic detoxification. In order to further explore the detoxification effect of detoxification enzymes on (S)-(-)-palasonin in P. xylostella, the effects of (S)-(-)-palasonin on enzyme activity and transcription level were determined, and the detoxification and metabolism of GSTs on (S)-(-)-palasonin were studied by in vitro inhibition and metabolism experiments. During this study, GST enzyme activity was significantly increased in P. xylostella after (S)-(-)-palasonin treatment. The expression levels of 19 GSTs genes were significantly increased whereas the expression levels of 1 gene decreased. Furthermore, (S)-(-)-palasonin is shown to be stabilized with GSTs and metabolized GSTs (GSTd1, GSTd2, GSTs1 and GSTs2) in vitro, with the highest metabolic rate of 80.59% for GSTs1. This study advances the beneficial utilization of (S)-(-)-palasonin as a botanical pesticide to control P. xylostella in the field.

Glutathione S-transferase (GST) genes and their function associated with pyrethroid resistance in the malaria vector Anopheles sinensis

BACKGROUND

Glutathione S-transferases (GSTs), a multifunctional protein family, are involved in insecticide resistance. However, a systematic analysis of GSTs in Anopheles sinensis, an important vector for malaria transmission, is lacking. In this study, we investigated the diversity and characteristics of GST genes, and analyzed their expression patterns and functions associated with insecticide resistance in this species.

RESULTS

We identified 32 putative cytosolic and three putative microsomal GST genes in the An. sinensis genome. Transcriptome analysis showed that GSTs were highly expressed in larvae, and mainly expressed in the antennae, midgut and Malpighian tubules of adults. In addition, we found that GSTd2 and GSTe2 were significantly upregulated in four An. sinensis pyrethroid-resistant field populations. Furthermore, silencing of GSTd2 and GSTe2 significantly increased the susceptibility of An. sinensis to deltamethrin, and recombinant GSTd2 and GSTe2 exhibited high enzymatic activity in the metabolism of 1-chloro-2,4-dinitrobenzene and dichlorodiphenyltrichloroethane (DDT).

CONCLUSION

These results showed that GSTs are involved in the development of insecticide resistance in An. sinensis through transcriptional overexpression and enzymatic metabolization, facilitating our understanding of insecticide resistance in insects. © 2022 Society of Chemical Industry.

The Acaricidal Potential of a New Agent GC16 for Tetranychus pueraricola (Acari: Tetranychidae) Based on Developmental Performance and Physiological Enzyme Activity

The spider mite, Tetranychus pueraricola (Ehara & Gotoh; Acari: Tetranychidae), is a serious pest in agriculture and horticulture. Application of chemical pesticides is the main mode of this pest control. Due to pesticide residues and resistance-induced resurgence of pests, there is a need to discover alternatives for spider mite management. GC16 comprises a mixture of calcium chloride (CaCl2, 45%) and lecithin (55%), which was recently found to have acaricidal properties. We evaluated the sublethal effects of GC16 on T. pueraricola using life table and enzyme [catalase (CAT), peroxidase (POD), superoxide dismutase (SOD), carboxylesterase (CarE), glutathione S-transferases (GST), and Ca2+-ATPase (Ca2+-ATP)] activity assays. The results showed that fecundity of T. pueraricola increased at LC30 but decreased at LC50 of GC16. The intrinsic rate of increase (r) of T. pueraricola decreased under the LC30 and LC50 of GC16. GC16 concentration and exposure time significantly influenced the activities of CAT, POD, CarE, GST, and Ca2+-ATP in adult mites. Twelve hours later after the treatment, GST and Ca2+-ATP activities were significantly inhibited by LC30 but enhanced by LC50. Moreover, the demographic parameter r and enzyme activities were negatively correlated. In sum, sublethal amounts of GC16 had an adverse effect on mites, and there was a trade-off between developmental performance and physiological enzyme activity of mites under GC16 stress, and GC16 showed an acaricidal potential for T. pueraricola. This work provides guidance for the application of GC16 to control T. pueraricola.

A glutathione S-transferase (BdGSTd9) participates in malathion resistance via directly depleting malathion and its toxic oxide malaoxon in Bactrocera dorsalis (Hendel)

BACKGROUND

The oriental fruit fly, Bactrocera dorsalis (Hendel), is a widespread agricultural pest that has evolved resistance to many commonly used insecticides including malathion. Glutathione S-transferases (GSTs) are multifunctional enzymes that metabolize insecticides directly or indirectly. The specific mechanism used by GSTs to confer malathion resistance in B. dorsalis is unclear.

RESULTS

BdGSTd9 was identified from B. dorsalis and was expressed at twice the level in a malathion-resistant strain (MR) than in a susceptible strain (MS). By using RNAi of BdGSTd9, the toxicity of malathion against MR was increased. Protein modelling and docking of BdGSTd9 with malathion and malaoxon indicated key amino acid residues for direct binding in the active site. In vitro assays with engineered Sf9 cells overexpressing BdGSTd9 demonstrated lower cytotoxicity of malathion. High performance liquid chromatography (HPLC) analysis indicated that malathion could be broken down significantly by BdGSTd9, and it also could deplete the malathion metabolite malaoxon, which possesses a higher toxicity to B. dorsalis. Taken together, the BdGSTd9 of B. dorsalis could not only deplete malathion, but also react with malaoxon and therefore enhance malathion resistance.

CONCLUSION

BdGSTd9 is a component of malathion resistance in B. dorsalis. It acts by depleting both malathion and malaoxon. © 2020 Society of Chemical Industry.

Characterization of Esterase Genes Involving Malathion Detoxification and Establishment of an RNA Interference Method in Liposcelis bostrychophila

Esterases (ESTs) play important roles in metabolizing various physiologically endogenous and exogenous compounds, and various environmental xenobiotics in insects. The psocid, Liposcelis bostrychophila is a major pest of stored products worldwide and rapidly develops resistance to commonly insecticides. However, the involvement of ESTs in insecticide metabolization and the application of RNAi approach in psocids have not been well elucidated. In this study, we characterized four LbEST genes and investigated the transcriptional levels of these genes at different developmental stages and under different insecticides exposures to assess their potential roles in response to insecticides. The four LbESTs contain a catalytic triad (Ser-His-Glu) linked to an oxyanion hole and acyl pocket involved in substrate stabilization during its hydrolysis. Synergism observed with the esterase-inhibitor DEF suggests the involvement of esterases in malathion detoxification. LbESTs were expressed during the whole of developmental stages, but predominant abundance in the first nymphal instar and adult stage. The mRNA level of three LbEST genes (except for LbEST4) was induced (1.29- to 5.60 fold) in response to malathion or deltamethrin exposures, indicating that these esterases are involved in the detoxification process. Silencing of LbEST1, LbEST2 or LbEST3 through dsRNA feeding led to a higher mortality of psocids upon the malathion treatment compared to controls (1.83 to 2.69-fold), demonstrating that these esterase genes play roles in malathion detoxification in L. bostrychophila. Our study provides new evidence for understanding of the function and regulation mechanism of esterases in L. bostrychophila in insecticide detoxification. The current study also suggests that the present RNAi method could be applied for gene functional studies in psocids.

Characterisation of GST genes from the Hyphantria cunea and their response to the oxidative stress caused by the infection of Hyphantria cunea nucleopolyhedrovirus (HcNPV)

The fall webworm, Hyphantria cunea (Drury) (Lepidoptera: Noctuidae), is a major pest found in forests. In this study, the effects of Hyphantria cunea nucleopolyhedrovirus (HcNPV) infection on the transcription levels and activities of glutathione S-transferases (GSTs) in H. cunea were determined. In the present study, 18 GST family genes were identified from the H. cunea transcriptome dataset by using bioinformatic analyses. These GST genes were classified into cytosolic (15 genes) and microsomal (three genes) classes. The 15 cytosolic GST genes belonged to four different subclasses (epsilon, sigma and delta). The all GST genes, especially GSTe4, showed high expression levels in egg and 1st~4th instar larval stage while their low expression levels in 5th~7th instar larvae using real-time quantitative PCR analysis. However, the expression levels of the 18 GST genes were varied after exposure to sublethal doses of HcNPV. The expression levels of most GSTs were downregulated and upregulated at low and high concentrations of HcNPV, respectively. The corresponding total GST activities also showed similar patterns. In H. cunea, changes in the expression levels and enzymatic activities of GSTs after exposure to HcNPV indicated that they may have important functions in the defense against HcNPV, and the stress, which may be reflected by the high GST enzymatic activities.

Functional Analysis of an Epsilon-Class Glutathione S-Transferase From Nilaparvata lugens (Hemiptera: Delphacidae)

Glutathione conjugation is a crucial step in xenobiotic detoxification. In the current study, we have functionally characterized an epsilon-class glutathione S-transferase (GST) from a brown planthopper Nilaparvata lugens (nlGSTE). The amino acid sequence of nlGSTE revealed approximately 36-44% identity with epsilon-class GSTs of other species. The recombinant nlGSTE was prepared in soluble form by bacterial expression and was purified to homogeneity. Mutation experiments revealed that the putative substrate-binding sites, including Phe107, Arg112, Phe118, and Phe119, were important for glutathione transferase activity. Furthermore, inhibition study displayed that nlGSTE activity was affected by insecticides, proposing that, in brown planthopper, nlGSTE could recognize insecticides as substrates.

Effects of phenol on glutathione S-transferase expression and enzyme activity in Chironomus kiiensis larvae

Detoxifying enzyme mRNAs are potentially useful stress biomarkers. Glutathione S-transferase (GST) metabolises lipophilic organic contaminants and mitigates oxidative damage caused by environmental pollutants. Herein, 12 Chironomus kiiensis GSTs (CkGSTs1-6, CkGSTt1-2, CkGSTd1-2, CkGSTm1-2) were cloned and grouped into sigma, theta, delta and microsomal subclasses. Open reading frames (450-699 bp) encode 170-232 amino acid proteins with predicted molecular masses of 17.31-26.84 kDa and isoelectric points from 4.94 to 9.58. All 12 GSTs were expressed during all tested developmental stages, and 11 displayed higher expression in fourth-instar larvae than eggs. GST activity after 24 h of phenol exposure was used to estimate environmental phenol contamination. After exposure to sublethal concentrations of phenol for 48 h, expression and activity of CkGSTs were inhibited in C. kiiensis larvae. Expression of CkGSTd1-2 and CkGSTs1-2 varied with phenol concentration, indicating potential use as biomarkers for monitoring environmental phenol contamination.

Insecticides induce the co-expression of glutathione S-transferases through ROS/CncC pathway in Spodoptera exigua

Glutathione S-transferases (GSTs) are a family of multifunctional enzymes that are involved in detoxification of electrophilic toxic compounds. Although the co-induced expression of GST genes by insecticides in insects has been documented in recent years, the underlying regulatory mechanisms are not understood. In this study, a total of thirty-one cytosolic S. exigua GSTs (SeGSTs) was cloned and identified. The bioinformatics and gene expression patterns were also analyzed. Out of them, SeGSTe9, SeGSTs6, SeGSTe1, SeGSTe6, SeGSTe8, SeGSTe14, and SeGSTd1 were significantly co-expressed following exposure to three insecticides (lambda-cyhalothrin, chlorpyrifos and chlorantraniliprole). The analysis of upstream sequences revealed that all of these seven SeGSTs harbored CncC/Maf binding site. The luciferase reporter assay showed that the pGL3-SeGST promoter construct exhibited a significant increase in luciferase activities after exposure to insecticides, and mutation of CncC/Maf binding site diminish the induction effect. These data indicate that CncC/Maf pathway regulates the co-expression of GST genes in response to different insecticides in S. exigua. Insecticides significantly enhanced the ROS content and treatment with the ROS inhibitor N-acetylcysteine (NAC) decreased the insecticide-induced luciferase activities of the PGL3-GSTe6 promoter construct, but not the CncC-mutated construct. These results indicate that ROS mediates GST gene expression after exposure to insecticides through CncC/Maf pathway. Overall, these data show that insecticides induce the co-expression of glutathione S-transferases through the ROS/CncC pathway in S. exigua.

Identification and expression profiles of twenty-six glutathione S-transferase genes from rice weevil, Sitophilus oryzae (Coleoptera: Curculionidae)

The rice weevil, Sitophilus oryzae, is one of the most destructive pests in stored cereals products. In this study, 26 cDNAs encoding glutathione S-transferases (GSTs) were sequenced and characterized in S. oryzae. Phylogenetic analysis displayed the categorization of 26 GSTs into six different cytosolic classes, including two in the delta, twelve in epsilon, three in omega, six in sigma, two in theta, and one in zeta class. RT-qPCR assay illustrated that the relative expression of ten GST genes was significantly higher in adult stages than in larval and pupal developmental stages. Tissue-specific expression analysis revealed that the SoGSTe5, SoGSTe7, SoGSTe12, and SoGSTz1 were up-regulated in the midgut, SoGSTe2, SoGSTe6, and SoGSTs2 were up-regulated in the fat body, and three GSTs (SoGSTd1, SoGSTd2 and SoGSTe4) were up-regulated in Malpighian tubules. RT-qPCR indicated that five GST genes were over expressed after exposure to phosphine at various times and concentrations. The increase in GST gene expressions after phosphine exposure in S. oryzae may lead to an improved tolerance for fumigations and xenobiotics.

De novo transcriptomic analysis of the alimentary tract of the tephritid gall fly, Procecidochares utilis

The tephritid gall fly, Procecidochares utilis, is an important obligate parasitic insect of the malignant weed Eupatorium adenophorum which biosynthesizes toxic secondary metabolites. Insect alimentary tracts secrete several enzymes that are used for detoxification, including cytochrome P450s, glutathione S-transferases, and carboxylesterases. To explore the adaptation of P. utilis to its toxic host plant, E. adenophorum at molecular level, we sequenced the transcriptome of the alimentary tract of P. utilis using Illumina sequencing. Sequencing and de novo assembly yielded 62,443 high-quality contigs with an average length of 604 bp that were further assembled into 45,985 unigenes with an average length of 674 bp and an N50 of 983 bp. Among the unigenes, 30,430 (66.17%) were annotated by alignment against the NCBI non-redundant protein (Nr) database, while 16,700 (36.32%), 16,267 (35.37%), and 11,530 (25.07%) were assigned functions using the Clusters of Orthologous Groups (COG), Kyoto Encyclopedia of Genes and Genomes (KEGG), and Gene Ontology (GO) databases, respectively. Using the comprehensive transcriptome data set, we manually identified several important gene families likely to be involved in the detoxification of toxic compounds including 21 unigenes within the glutathione S-transferase (GST) family, 22 unigenes within the cytochrome P450 (P450) family, and 16 unigenes within the carboxylesterase (CarE) family. Quantitative PCR was used to verify eight, six, and two genes of GSTs, P450s, and CarEs, respectively, in different P. utilis tissues and at different developmental stages. The detoxification enzyme genes were mainly expressed in the foregut and midgut. Moreover, the unigenes were higher expressed in the larvae, pupae, and 3-day adults, while they were expressed at lower levels in eggs. These transcriptomic data provide a valuable molecular resource for better understanding the function of the P. utilis alimentary canal. These identified genes could be pinpoints to address the molecular mechanisms of P. utilis interacting with toxic plant host.

Multiple Glutathione S-Transferase Genes in Heortia vitessoides (Lepidoptera: Crambidae): Identification and Expression Patterns

To elucidate the role of glutathione S-transferases (GSTs) in Heortia vitessoides Moore (Lepidoptera: Crambidae), one of the most destructive defoliating pests in Aquilaria sinensis (Lour.) Gilg (Thymelaeaceae) forests, 16 GST cDNAs were identified in the transcriptome of adult H. vitessoides. All cDNAs included a complete open reading frame and were designated HvGSTd1-HvGSTu2. A phylogenetic analysis showed that the 16 HvGSTs were classified into seven different cytosolic classes; three in delta, two in epsilon, three in omega, three in sigma, one in theta, two in zeta, and two in unclassified. The expression patterns of these HvGSTs in various larval and adult tissues, following exposure to half the lethal concentrations (LC50s) of chlorantraniliprole and beta-cypermethrin, were determined using real-time quantitative polymerase chain reaction (RT-qPCR). The expression levels of the 16 HvGSTs were found to differ among various larval and adult tissues. Furthermore, the RT-qPCR confirmed that the transcription levels of nine (HvGSTd1, HvGSTd3, HvGSTe2, HvGSTe3, HvGSTo3, HvGSTs1, HvGSTs3, HvGSTu1, and HvGSTu2) and six (HvGSTd1, HvGSTd3, HvGSTe2, HvGSTo2, HvGSTs1, and HvGSTu1) HvGST genes were significantly higher in the fourth-instar larvae following exposure to the insecticides chlorantraniliprole and beta-cypermethrin, respectively. These genes are potential candidates involved in the detoxification of these two insecticides. Further studies utilizing the RNA interference approach are required to enhance our understanding of the functions of these genes in this forest pest.