Insect glutathione transferases and insecticide resistance

Combined effects of three insecticides with different modes of action on biochemical responses of the solitary bee Osmia bicornis

Bees are simultaneously exposed to a variety of pesticides, which are often applied in mixtures and can cause lethal and sublethal effects. The combined effects of pesticides, however, are not measured in the current risk assessment schemes. Additionally, the sublethal effects of pesticides on a variety of physiological processes are poorly recognized in bees, especially in non-Apis solitary bees. In this study, we used a full-factorial design to examine the main and interactive effects of three insecticide formulations with different modes of action (Mospilan 20 SP, Sherpa 100 EC, and Dursban 480 EC) on bee biochemical processes. We measured acetylcholinesterase (AChE), glutathione S-transferase (GST) and esterase (EST) activities, as well as a nonenzymatic biomarker associated with energy metabolism, i.e., ATP level. All studied endpoints were affected by Sherpa 100 EC, and the activities of AChE and EST as well as ATP levels were affected by Dursban 480 EC. Moreover, complex interactions between all three insecticides affected ATP levels, showing outcomes that cannot be predicted when testing each insecticide separately. The results indicate that even if interactive effects are sometimes difficult to interpret, there is a need to study such interactions if laboratory-generated toxicity data are to be extrapolated to field conditions.

Functional Analysis of Insecticide Inhibition and Metabolism of Six Glutathione S-Transferases in the Rice Stem Borer, Chilo suppressalis

The glutathione S-transferases (GSTs) are important detoxifying enzymes in insects. Our previous studies found that the susceptibility of Chilo suppressalis to abamectin was significantly increased when the CsGST activity was inhibited by glutathione (GSH) depletory. In this study, the potential detoxification mechanisms of CsGSTs to abamectin were explored. Six CsGSTs of C. suppressalis were expressed in vitro. Enzymatic kinetic parameters including Km and Vmax of recombinant CsGSTs were determined, and results showed that all of the six CsGSTs were catalytically active and displaying glutathione transferase activity. Insecticide inhibitions revealed that a low concentration of abamectin could effectively inhibit the activities of CsGSTs including CsGSTd1, CsGSTe4, CsGSTo2, CsGSTs3, and CsGSTu1. However, the in vitro metabolism assay found that the six CsGSTs could not metabolize abamectin directly. Additionally, the glutathione transferase activity of CsGSTs in C. suppressalis was significantly increased post-treatment with abamectin. Comprehensive analysis of the results in present and our previous studies demonstrated that CsGSTs play an important role in detoxification of abamectin by catalyzing the conjugation of GSH to abamectin in C. suppressalis, and the high binding affinities of CsGSTd1, CsGSTe4, CsGSTo2, CsGSTs3, and CsGSTu1 with abamectin might also suggest the involvement of CsGSTs in detoxification of abamectin via the noncatalytic passive binding and sequestration instead of direct metabolism. These studies are helpful to better understand the detoxification mechanisms of GSTs in insects.

Molecular Cloning, Expression and Enzymatic Characterization of Tetrahymena thermophila Glutathione-S-Transferase Mu 34

Glutathione-S-transferase enzymes (GSTs) are essential components of the phase II detoxification system and protect organisms from oxidative stress induced by xenobiotics and harmful toxins such as 1-chloro-2,4-dinitrobenzene (CDNB). In Tetrahymena thermophila, the TtGSTm34 gene was previously reported to be one of the most responsive GST genes to CDNB treatment (LD50 = 0.079 mM). This study aimed to determine the kinetic features of recombinantly expressed and purified TtGSTm34 with CDNB and glutathione (GSH). TtGSTm34-8xHis was recombinantly produced in T. thermophila as a 25-kDa protein after the cloning of the 660-bp full-length ORF of TtGSTm34 into the pIGF-1 vector. A three-dimensional model of the TtGSTm34 protein constructed by the AlphaFold and PyMOL programs confirmed that it has structurally conserved and folded GST domains. The recombinant production of TtGSTm34-8xHis was confirmed by SDS‒PAGE and Western blot analysis. A dual-affinity chromatography strategy helped to purify TtGSTm34-8xHis approximately 3166-fold. The purified recombinant TtGSTm34-8xHis exhibited significantly high enzyme activity with CDNB (190 µmol/min/mg) as substrate. Enzyme kinetic analysis revealed Km values of 0.68 mM with GSH and 0.40 mM with CDNB as substrates, confirming its expected high affinity for CDNB. The optimum pH and temperature were determined to be 7.0 and 25 °C, respectively. Ethacrynic acid inhibited fully TtGSTm34-8xHis enzyme activity. These results imply that TtGSTm34 of T. thermophila plays a major role in the detoxification of xenobiotics, such as CDNB, as a first line of defense in aquatic protists against oxidative damage.

Ecotoxicological strategies employing biochemical markers and organisms to monitor the efficacy of malathion photolysis treatment

The objective of this study was to assess the photolysis-mediated degradation of malathion in standard and commercial formulations, and to determine the toxicity of these degraded formulations. Degradation tests were carried out with 500 μg L-1 of malathion and repeated three times. The initial and residual toxicity was assessed by using Lactuca sativa seeds for phytotoxicity, Stegomyia aegypti larvae for acute toxicity, and Stegomyia aegypti mosquitoes (cultivated from the larval stage until emergence as mosquitoes) to evaluate the biochemical markers of sublethal concentrations. For the standard formulations the photolytic process efficiently reduced the initial concentration of malathion to levels below the regulatory limits however, the formation of byproducts was revealed by chromatography, which allowed for a more complete proposal of photolytic-mediated malathion degradation route. The degraded formulations inhibited the growth of L. sativa seeds, while only the untreated formulations showed larvicidal activity and mortality. Both formulations slightly inhibited acetylcholinesterase activity in S. aegypti mosquitoes, while the standard formulation decreased and the commercial formulation increased glutathione S-transferase activity. However, there were no significant differences for superoxide dismutase, esterase-α, esterase-β and lipid peroxidation. These findings indicate that in the absence of the target compound, the presence of byproducts can alter the enzymatic activity. In general, photolysis effectively degrade malathion lower than the legislation values; however, longer treatment times must be evaluated for the commercial formulation.

Suppressing the expression of glutathione S-transferase gene GSTd10 increases the sensitivity of Zeugodacus cucurbitae against β-cypermethrin

Zeugodacus cucurbitae Coquillett (Diptera: Tephritidae) is an agriculturally and economically important pest worldwide that has developed resistance to β-cypermethrin. Glutathione S-transferases (GSTs) have been reported to be involved in the detoxification of insecticides in insects. We have found that both ZcGSTd6 and ZcGSTd10 were up-regulated by β-cypermethrin induction in our previous study, so we aimed to explore their potential relationship with β-cypermethrin tolerance in this study. The heterologous expression of ZcGSTd6 and ZcGSTd10 in Escherichia coli showed significantly high activities against 1-chloro-2,4-dinitrobenzene (CDNB). The kinetic parameters of ZcGSTd6 and ZcGSTd10 were determined by Lineweaver-Burk. The Vmax and Km of ZcGSTd6 were 0.50 μmol/min·mg and 0.3 mM, respectively. The Vmax and Km of ZcGSTd10 were 1.82 μmol/min·mg and 0.53 mM. The 3D modelling and molecular docking results revealed that β-cypermethrin exhibited a stronger bounding to the active site SER-9 of ZcGSTd10. The sensitivity to β-cypermethrin was significantly increased by 18.73% and 27.21%, respectively, after the knockdown of ZcGSTd6 and ZcGSTd10 by using RNA interference. In addition, the inhibition of CDNB at 50% (IC50) and the inhibition constants (Ki) of β-cypermethrin against ZcGSTd10 were determined as 0.41 and 0.33 mM, respectively. The Ki and IC50 of β-cypermethrin against ZcSGTd6 were not analysed. These results suggested that ZcGSTd10 could be an essential regulator involved in the tolerance of Z. cucurbitae to β-cypermethrin.

Insects to the rescue? Insights into applications, mechanisms, and prospects of insect-driven remediation of organic contaminants

Traditional and emerging contaminants pose significant human and environmental health risks. Conventional physical, chemical, and bioremediation techniques have been extensively studied for contaminant remediation. However, entomo- or insect-driven remediation has received limited research and public attention. Entomo-remediation refers to the use of insects, their associated gut microbiota, and enzymes to remove or mitigate organic contaminants. This novel approach shows potential as an eco-friendly method for mitigating contaminated media. However, a comprehensive review of the status, applications, and challenges of entomo-remediation is lacking. This paper addresses this research gap by examining and discussing the evidence on entomo-remediation of various legacy and emerging organic contaminants. The results demonstrate the successful application of entomo-remediation to remove legacy organic contaminants such as persistent organic pollutants. Moreover, entomo-remediation shows promise in removing various groups of emerging contaminants, including microplastics, persistent and emerging organic micropollutants (e.g., antibiotics, pesticides), and nanomaterials. Entomo-remediation involves several insect-mediated processes, including bio-uptake, biotransfer, bioaccumulation, and biotransformation of contaminants. The mechanisms underlying the biotransformation of contaminants are complex and rely on the insect gut microbiota and associated enzymes. Notably, while insects facilitate the remediation of contaminants, they may also be exposed to the ecotoxicological effects of these substances, which is often overlooked in research. As an emerging field of research, entomo-remediation has several knowledge gaps. Therefore, this review proposes ten key research questions to guide future perspectives and advance the field. These questions address areas such as process optimization, assessment of ecotoxicological effects on insects, and evaluation of potential human exposure and health risks.

Glutathione S-Transferase Genes Involved in Response to Short-Term Heat Stress in Tetranychus urticae (Koch)

Tetranychus urticae, a globally ubiquitous mite, poses a significant threat to agriculture. Elevated temperatures exacerbate the growth, development, and reproduction of T. urticae, leading to substantial crop damage. In this study, we employed comparative transcriptomic approaches with whole-genome information of T. urticae to identify six Glutathione S-transferase genes (GSTs) implicated in heat stress response. Through comprehensive bioinformatics analyses, we elucidated the tertiary structure and active sites of the corresponding proteins, providing a thorough characterization of these GST genes. Furthermore, we investigated the expression patterns of these six GST genes under short-term heat shock conditions. Our findings unveiled the involvement of T. urticae GST genes in combating oxidative stress induced by heat, underscoring their role in antioxidant defense mechanisms. This study contributes valuable insights into the molecular mechanisms underlying the response of T. urticae to heat stress, laying a foundation for the development of strategies aimed at mitigating its impact in high-temperature environments.

Transcriptomic analysis of Anopheles gambiae from Benin reveals overexpression of salivary and cuticular proteins associated with cross-resistance to pyrethroids and organophosphates

BACKGROUND

Insecticide resistance (IR) is one of the major threats to malaria vector control programs in endemic countries. However, the mechanisms underlying IR are poorly understood. Thus, investigating gene expression patterns related to IR can offer important insights into the molecular basis of IR in mosquitoes. In this study, RNA-Seq was used to characterize gene expression in Anopheles gambiae surviving exposure to pyrethroids (deltamethrin, alphacypermethrin) and an organophosphate (pirimiphos-methyl).

RESULTS

Larvae of An. gambiae s.s. collected from Bassila and Djougou in Benin were reared to adulthood and phenotyped for IR using a modified CDC intensity bottle bioassay. The results showed that mosquitoes from Djougou were more resistant to pyrethroids (5X deltamethrin: 51.7% mortality; 2X alphacypermethrin: 47.4%) than Bassila (1X deltamethrin: 70.7%; 1X alphacypermethrin: 77.7%), while the latter were more resistant to pirimiphos-methyl (1.5X: 48.3% in Bassila and 1X: 21.5% in Djougou). RNA-seq was then conducted on resistant mosquitoes, non-exposed mosquitoes from the same locations and the laboratory-susceptible An. gambiae s.s. Kisumu strain. The results showed overexpression of detoxification genes, including cytochrome P450s (CYP12F2, CYP12F3, CYP4H15, CYP4H17, CYP6Z3, CYP9K1, CYP4G16, and CYP4D17), carboxylesterase genes (COEJHE5E, COE22933) and glutathione S-transferases (GSTE2 and GSTMS3) in all three resistant mosquito groups analyzed. Genes encoding cuticular proteins (CPR130, CPR10, CPR15, CPR16, CPR127, CPAP3-C, CPAP3-B, and CPR76) were also overexpressed in all the resistant groups, indicating their potential role in cross resistance in An. gambiae. Salivary gland protein genes related to 'salivary cysteine-rich peptide' and 'salivary secreted mucin 3' were also over-expressed and shared across all resistant groups.

CONCLUSION

Our results suggest that in addition to metabolic enzymes, cuticular and salivary gland proteins could play an important role in cross-resistance to multiple classes of insecticides in Benin. These genes warrant further investigation to validate their functional role in An. gambiae resistance to insecticides.

Identification and Functional Characterization of an Omega-Class Glutathione Gene PcGSTO1 Associated with Cyetpyrafen Resistance in Panonychus citri (McGregor)

Cyetpyrafen is a recently developed acaricide. The citrus red mite, Panonychus citri (McGregor), has developed significant resistance to cyetpyrafen. However, the molecular mechanism underlying the cyetpyrafen resistance in P. citri remains unclear. Glutathione S-transferases (GSTs) play a critical role in arthropod pesticide resistance. This study showed that GSTs were potentially related to the resistance of P. citri to cyetpyrafen through synergistic experiments and enzyme activity analysis. An omega-family GST gene, PcGSTO1, was significantly up-regulated in the egg, nymph, and adult stages of the cyetpyrafen-resistant strain. Additionally, silencing of PcGSTO1 significantly increased the mortality of P. citri to cyetpyrafen and recombinant PcGSTO1 demonstrated the ability to metabolize cyetpyrafen. Our results indicated that the overexpression of PcGSTO1 is associated with cyetpyrafen resistance in P. citri, and they also provided valuable information for managing resistance in P. citri.

miR-317-3p and miR-283-5p Play a Crucial Role in Regulating the Resistance to Indoxacarb in Spodoptera frugiperda by Targeting GSTs4

Spodoptera frugiperda is primarily controlled through chemical insecticides. Our RNA-seq data highlight the overexpression of GSTs4 in indoxacarb-resistant S. frugiperda. However, the exact role of GSTs4 in indoxacarb resistance and its regulatory mechanisms remains elusive. Therefore, we investigated the functional role of GSTs4 in S. frugiperda and explored the underlying post-transcriptional regulatory mechanisms. GSTs4 was highly overexpressed (27.6-fold) in the indoxacarb-resistant strain, and GSTs4 silencing significantly increases the susceptibility of S. frugiperda to indoxacarb, increasing mortality by 27.3%. miR-317-3p and miR-283-5p can bind to the 3'UTR of GSTs4, and the targeting relationship was confirmed by dual-luciferase reporter assays. Injecting miR-317-3p and miR-283-5p agomirs reduces GSTs4 levels by 64.8 and 42.3%, respectively, resulting in an increased susceptibility of S. frugiperda to indoxacarb. Conversely, the administration of miR-317-3p and miR-283-5pantagomirs increases GSTs4 expression and reduces larval susceptibility to indoxacarb. These findings demonstrate that miR-317-3p and miR-283-5p contribute to indoxacarb resistance in S. frugiperda by regulating the overexpression of GSTs4.

Insight into Hyalomma anatolicum biology by comparative genomics analyses

Hyalomma anatolicum is an obligatory blood-sucking ectoparasite and contributes to the transmission of Crimean-Congo haemorrhagic fever (CCHF) virus, Theileria spp. and Babesia spp. Progress in exploring the adaptive strategy of this ectoparasite and developing tools to fight it has been hindered by the lack of a complete genome. Herein, we assembled the genome using diverse sources of data from multiple sequencing platforms and annotated the 1.96 Gb genome of Hy. anatolicum. Comparative genome analyses and the predicted protein encoding genes reveal unique facets of this genome, including gene family expansion associated with blood feeding and digestion, multi-gene families involved in detoxification, a great number of neuropeptides and corresponding receptors regulating tick growth, development, and reproduction, and glutathione S-transferase genes playing roles in insecticide resistance and detoxification of multiple xenobiotic factors. This high quality reference genome provides fundamental data for obtaining insights into a variety of aspects of tick biology and developing novel strategies to fight notorious tick vectors of human and animal pathogens.

Changes in transcriptome regulations of a marine rotifer Brachionus plicatilis under methylmercury stress

Mercury (Hg), a heavy metal pollutant worldwide, can be transformed into methylmercury (MeHg) by various aquatic microorganisms in water, thus accumulating along the aquatic food chain and posing a particular challenge to human health. Zooplankton plays a crucial role in aquatic ecosystems and serves as a major component of the food chain. To evaluate the effects of MeHg on the rotifer Brachionus plicatilis and reveal the underlying mechanism of these effects, we exposed B. plicatilis to MeHg by either direct immersion or by feeding with MeHg-poisoned Chlorella pyrenoidesa, respectively, and conducted a transcriptomic analysis. The results showed that B. plicatilis directly exposed to MeHg by immersion showed significant enrichment of the glutathione metabolism pathway for detoxification of MeHg. In addition, the exposure to MeHg by feeding induced a significant enrichment of lysosome and notch signaling pathways of rotifers, supporting the hypothesis that MeHg can induce autophagy dysfunction in cells and disturb the nervous system of rotifers. In two different routes of MeHg exposure, the pathway of cytochrome P450 in rotifers showed significant enrichment for resisting MeHg toxicity. Our results suggest further studies on the potential mechanism and biological responses of MeHg toxicity in other links of the aquatic food chain.

Unclassified glutathione-S-transferase AiGSTu1 confers chlorantraniliprole tolerance in Agrotis ipsilon

BACKGROUND

Chlorantraniliprole (CAP) is a diamide insecticide with high efficacy against many pest insects, including the black cutworm, Agrotis ipsilon. Agrotis ipsilon is a serious pest causing significant yield losses in crops. Glutathione-S-transferases (GSTs) belong to a family of metabolic enzymes that can detoxify a wide range of pesticides. However, little is known about the functions of GSTs in CAP tolerance in A. ipsilon.

RESULTS

A cDNA sequence (designated AiGSTu1) encoding an unclassified GST was identified from A. ipsilon. AiGSTu1 is highly expressed during the 3rd -instar larval and the pupal stages. Most of the mRNA transcripts were found in larval Malpighian tubules. Exposure to CAP strongly enhanced AiGSTu1 expression, GST activity, hydrogen peroxide (H2 O2 ) and malondialdehyde levels in larvae. H2 O2 treatment upregulated the transcription level of AiGSTu1, suggesting that CAP-induced oxidative stress may activate AiGSTu1 expression. The activity of recombinant AiGSTu1 was inhibited by CAP in a dose-dependent manner. Metabolism assay results demonstrated that AiGSTu1 is capable of depleting CAP. Overexpression of AiGSTu1 enhanced the tolerance of Escherichia coli cells to H2 O2 and the oxidative stress inducer, cumene hydroperoxide. Silencing of AiGSTu1 by RNA interference increased the susceptibility of A. ipsilon larvae to CAP.

CONCLUSION

The findings of this study provide valuable insights into the potential role of AiGSTu1 in CAP detoxification and will improve our understanding of CAP tolerance in A. ipsilon. © 2023 Society of Chemical Industry.

Cloning of three epsilon-class glutathione S-transferase genes from Micromelalopha troglodyta (Graeser) (Lepidoptera: Notodontidae) and their response to tannic acid

Micromelalopha troglodyta (Graeser) is an important pest of poplar in China, and glutathione S-transferase (GST) is an important detoxifying enzyme in M. troglodyta. In this paper, three full-length GST genes from M. troglodyta were cloned and identified. These GST genes all belonged to the epsilon class (MtGSTe1, MtGSTe2, and MtGSTe3). Furthermore, the expression of these three MtGSTe genes in different tissues, including midguts and fat bodies, and the MtGSTe expression in association with different concentrations of tannic acid, including 0.001, 0.01, 0.1, 1, and 10 mg ml-1, were analysed in detail. The results showed that the expression levels of MtGSTe1, MtGSTe2, and MtGSTe3 were all the highest in the fourth instar larvae; the expression levels of MtGSTe1 and MtGSTe3 were the highest in fat bodies, while the expression level of MtGSTe2 was the highest in midguts. Furthermore, the expression of MtGSTe mRNA was induced by tannic acid in M. troglodyta. These studies were helpful to clarify the interaction between plant secondary substances and herbivorous insects at a deep level and provided a theoretical foundation for controlling M. troglodyta.

Key Contributions of the Overexpressed Plutella xylostella Sigma Glutathione S-Transferase 1 Gene (PxGSTs1) in the Resistance Evolution to Multiple Insecticides

The overexpression of insect detoxification enzymes is a typical adaptive evolutionary strategy for insects to cope with insecticide pressure. In this study, we identified a glutathione S-transferase (GST) gene, PxGSTs1, that exhibited pronounced expression in the field-resistant population of Plutella xylostella. By using RNAi (RNA interference), the transgenic fly models, and quantitative real-time polymerase chain reaction (RT-qPCR) methods, we confirmed that the augmented expression of PxGSTs1 mediates the resistance of P. xylostella to various types of insecticides, including chlorantraniliprole, novaluron, λ-cyhalothrin, and abamectin. PxGSTs1 was found to bolster insecticide resistance in two ways: direct detoxification and enhancing antioxidative defenses. In addition, our findings demonstrated that pxy-miR-8528a exerts a pivotal influence on forming insecticide resistance in P. xylostella by downregulating PxGSTs1 expression. In summary, we elucidated the multifaceted molecular and biochemical underpinnings of PxGSTs1-driven insecticide resistance in P. xylostella. Our results provide a new perspective for understanding the insecticide resistance mechanism of P. xylostella.

Architecture and potential roles of a delta-class glutathione S-transferase in protecting honey bee from agrochemicals

The European honey bee, Apis mellifera, serves as the principle managed pollinator species globally. In recent decades, honey bee populations have been facing serious health threats from combined biotic and abiotic stressors, including diseases, limited nutrition, and agrochemical exposure. Understanding the molecular mechanisms underlying xenobiotic adaptation of A. mellifera is critical, considering its extensive exposure to phytochemicals and agrochemicals present in the environment. In this study, we conducted a comprehensive structural and functional characterization of AmGSTD1, a delta class glutathione S-transferase (GST), to unravel its roles in agrochemical detoxification and antioxidative stress responses. We determined the 3-dimensional (3D) structure of a honey bee GST using protein crystallography for the first time, providing new insights into its molecular structure. Our investigations revealed that AmGSTD1 metabolizes model substrates, including 1-chloro-2,4-dinitrobenzene (CDNB), p-nitrophenyl acetate (PNA), phenylethyl isothiocyanate (PEITC), propyl isothiocyanate (PITC), and the oxidation byproduct 4-hydroxynonenal (HNE). Moreover, we discovered that AmGSTD1 exhibits binding affinity with the fluorophore 8-Anilinonaphthalene-1-sulfonic acid (ANS), which can be inhibited with various herbicides, fungicides, insecticides, and their metabolites. These findings highlight the potential contribution of AmGSTD1 in safeguarding honey bee health against various agrochemicals, while also mitigating oxidative stress resulting from exposure to these substances.

Phylogenomics of the Ecdysteroid Kinase-like (EcKL) Gene Family in Insects Highlights Roles in Both Steroid Hormone Metabolism and Detoxification

The evolutionary dynamics of large gene families can offer important insights into the functions of their individual members. While the ecdysteroid kinase-like (EcKL) gene family has previously been linked to the metabolism of both steroid molting hormones and xenobiotic toxins, the functions of nearly all EcKL genes are unknown, and there is little information on their evolution across all insects. Here, we perform comprehensive phylogenetic analyses on a manually annotated set of EcKL genes from 140 insect genomes, revealing the gene family is comprised of at least 13 subfamilies that differ in retention and stability. Our results show the only two genes known to encode ecdysteroid kinases belong to different subfamilies and therefore ecdysteroid metabolism functions must be spread throughout the EcKL family. We provide comparative phylogenomic evidence that EcKLs are involved in detoxification across insects, with positive associations between family size and dietary chemical complexity, and we also find similar evidence for the cytochrome P450 and glutathione S-transferase gene families. Unexpectedly, we find that the size of the clade containing a known ecdysteroid kinase is positively associated with host plant taxonomic diversity in Lepidoptera, possibly suggesting multiple functional shifts between hormone and xenobiotic metabolism. Our evolutionary analyses provide hypotheses of function and a robust framework for future experimental studies of the EcKL gene family. They also open promising new avenues for exploring the genomic basis of dietary adaptation in insects, including the classically studied coevolution of butterflies with their host plants.

Exploring the molecular mechanisms of increased intensity of pyrethroid resistance in Central African population of a major malaria vector Anopheles coluzzii

Molecular mechanisms driving the escalation of pyrethroid resistance in the major malaria mosquitoes of Central Africa remain largely uncharacterized, hindering effective management strategies. Here, resistance intensity and the molecular mechanisms driving it were investigated in a population of Anopheles coluzzii from northern Cameroon. High levels of pyrethroid and organochloride resistance were observed in An. coluzzii population, with no mortality for 1× permethrin; only 11% and 33% mortalities for 5× and 10× permethrin diagnostic concentrations, and <2% mortalities for deltamethrin and DDT, respectively. Moderate bendiocarb resistance (88% mortality) and full susceptibility to malathion were observed. Synergist bioassays with piperonyl butoxide recovered permethrin susceptibility, with mortalities increasing to 53.39%, and 87.30% for 5× and 10× permethrin, respectively, implicating P450 monooxygenases. Synergist bioassays with diethyl maleate (DEM) recovered permethrin and DDT susceptibilities (mortalities increasing to 34.75% and 14.88%, respectively), implicating glutathione S-transferases. RNA-seq-based genome-wide transcriptional analyses supported by quantitative PCR identified glutathione S-transferase, GSTe2 (RNA-seqFC = 2.93 and qRT-PCRFC = 8.4, p < 0.0043) and CYP450, CYP6Z2 (RNA-seqFC = 2.39 and qRT-PCRFC = 11.7, p < 0.0177) as the most overexpressed detoxification genes in the pyrethroid-resistant mosquitoes, compared to mosquitoes of the susceptible Ngousso colony. Other overexpressed genes include P450s, CYP6M2 (FC = 1.68, p < 0.0114), CYP4G16 (FC = 2.02, p < 0.0005), and CYP4G17 (FC = 1.86, p < 0.0276). While high frequency of the 1014F kdr mutation (50%) and low frequencies of 1014S (6.61%) and 1575Y (10.29%) were observed, no ace-1 mutation was detected in bendiocarb-resistant populations, suggesting the preeminent role of metabolic mechanism. Overexpression of metabolic resistance genes (including GSTe2 and CYP6Z2 known to confer resistance to multiple insecticides) in An. coluzzii from the Sudan Savannah of Cameroon highlights the need for alternative management strategies to reduce malaria burden in northern Cameroon.

The diverse functions of Mu-class Glutathione S-transferase HrGSTm1 during the development of Hyalomma rufipes with a focus on the detoxification metabolism of cyhalothrin

BACKGROUND

Glutathione S-transferases (GSTs) are a superfamily of multifunctional enzymes in living organisms with metabolic and detoxification functions, which can detoxify exogenous and endogenous compounds and thereby reduce the damage caused by toxic substances to the body. Ticks are obligate blood-sucking ectoparasites that can transmit various pathogens, and the characterization of tick-derived GSTs may help improve current understanding of the molecular mechanism of tick resistance to insecticides. In this study, a novel GST gene, named HrGSTm1, was identified from Hyalomma rufipes.

METHODS

Sequence analysis was performed by using bioinformatics techniques. A prokaryotic expression system was used to obtain the recombinant expression protein rHrGSTm1. Detection of spatiotemporal expression patterns of target genes and their response to the toxicity of cyhalothrin on female H. rufipes was performed by using a quantitative PCR platform. The optimal enzymological parameters of rHrGSTm1 using glutathione as substrate were calculated. The antioxidant capacity of the recombinant protein was evaluated by DPPH• (1,1-Diphenyl-2-picrylhydrazyl radical 2,2-Diphenyl-1-(2,4,6-trinitrophenyl) hydrazyl). Knockdown of the HrGSTm1 genes through RNA interference was used to analyze their effects on the physiological parameters of ticks. The changes in HrGSTm1 messenger RNA expression patterns under cypermethrin stress were analyzed.

RESULTS

The complementary DNA sequence of HrGSTm1 contained a 672-bp open reading frame, which potentially encoded 223 amino acids. The predicted molecular weight was 25.62 kDa, and the isoelectric point 8.22. HrGSTm1 is a Mu-class GST, belonging to the cytoplasmic GSTs with no signal peptide observed. The Vmax and Km of rHrGSTm1 were 3.367 ± 0.81 uM and 2.208 ± 0.76 uM, respectively, and its activities were dependent on different temperatures and pH conditions; the scavenging rate of rHrGSTm1 to DPPH• reached 76.4% at 1.25 mg/ml. Variable expressions of HrGSTm1 were observed under various treatment periods and in different tissues, with the highest appearing in eggs (analysis of variance [ANOVA], F(2, 9) = 279.9, P < 0.0001) and Malpighian tubules (ANOVA, F(3, 12) = 290.5, P < 0.0001). After knockdown of HrGSTm1, compared with the control group, the mortality in the treatment group was increased by 16.7%, the average oviposition rate decreased by 33.9%, the average engorged body weight decreased by 287.38 mg and egg weight decreased by 127.46 mg, although only the engorged body weight was significantly different (t-test, t(44) = 2.886, P = 0.006). After exposure to three sublethal concentrations (LC05, LC10, LC50) of cyhalothrin, the expression level of HrGSTm1 in the midgut, ovary and salivary gland was upregulated, whereas in Malpighian tubules, it showed a trend of upregulation at first and then downregulation, implying different functions during the detoxification in different tissues.

CONCLUSIONS

In this study, a novel GST of the Mu-class was successfully isolated from H. rufipes and systematically subjected to bioinformatic analysis and recombination identification. The variation trend of HrGSTm1 expression level in different tissues suggests that the gene has different detoxification functions in different tissues. The potential function of this gene was analyzed to provide basic research for further investigation of its detoxification mechanism.

Molecular and functional characterization of an antenna-enriched glutathione S-transferase BminGSTd3 involved in undecanol degradation in the citrus fruit fly, Bactrocera minax (Enderlein) (Diptera Tephritidae)

Bactrocera minax is a disastrous pest of citrus crops in China. Numerous studies focused on the molecular mechanism of odorant perception of B. minax, but the molecular mechanism of odorant degradation remains unclear. Glutathione S-transferases (GSTs) are considered as a class of odorant-degrading enzymes involved in degrading odorant molecules in insects' olfactory system. Here, we identified a delta-class GST gene, BminGSTd3, from B. minax. It was predominantly expressed in adult's olfactory organ antennae. The bacterially expressed recombinant BminGSTd3 was able to catalyze the conjugation of glutathione (GSH) with 2, 4-dinitrochlorobenzene (CDNB). Spectrophotometric analysis showed that undecanol can inhibit catalytic activities of BminGSTd3. Metabolic assays exhibited that undecanol can be depleted by BminGSTd3. Undecanol is believed to be an important B. minax sex pheromone component. The other components of the pheromone remain unclear. To understand how BminGSTd3 specifically recognizes undecanol, a 3D model of BminGSTd3 was constructed by homology modeling. Molecular docking based on this model revealed that E64 and S65 are the key amino acids recognizing undecanol, and this was proven by site-directed mutagenesis and intrinsic fluorescence assays. We suggest that BminGSTd3 is an undecanol metabolizing GST in B.minax, and E64 and S65 may serve as the key binding sites.

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.

Genetic independence between traits separated by metamorphosis is widespread but varies with biological function

Why is metamorphosis so pervasive? Does it facilitate the independent (micro)evolution of quantitative traits in distinct life stages, similarly to how it enables some limbs and organs to develop at specific life stages? We tested this hypothesis by measuring the expression of 6400 genes in 41 Drosophila melanogaster inbred lines at larval and adult stages. Only 30% of the genes showed significant genetic correlations between larval and adult expression. By contrast, 46% of the traits showed some level of genetic independence between stages. Gene ontology terms enrichment revealed that across stages correlated traits were often involved in proteins synthesis, insecticide resistance and innate immunity, while a vast number of genes expression traits associated with energy metabolism were independent between life stages. We compared our results to a similar case: genetic constraints between males and females in gonochoric species (i.e. sexual antagonism). We expected selection for the separation between males and females to be higher than between juvenile and adult functions, as gonochorism is a more common strategy in the animal kingdom than metamorphosis. Surprisingly, we found that inter-stage constraints were lower than inter-sexual genetic constraints. Overall, our results show that metamorphosis enables a large part of the transcriptome to evolve independently at different life stages.

Role of the epsilon glutathione S-transferases in xanthotoxin tolerance in Spodoptera litura

Spodoptera litura, a polyphagous lepidopteran pest, demonstrates a remarkable capacity to adapt to varying host plants by efficiently detoxifying phytochemicals. However, the underlying mechanism for this adaptation is not well understood. Herein, twenty eplison glutathione S-transferase genes (GSTes) were characterized and their roles in phytochemical tolerance were analyzed in S. litura. Most of the GSTe genes were mainly expressed in the larval midgut and fat body. Exposure to the phytochemicals, especially xanthotoxin, induced the expression of most GSTe genes. Molecular docking analysis revealed that xanthotoxin could form stable bonds with six xanthotoxin-responsive GSTes, with binding free energies ranging from -36.44 to -68.83 kcal mol-1. Knockdown of these six GSTe genes increased the larval susceptibility to xanthotoxin. Furthermore, xanthotoxin exposure significantly upregulated the expression of two transcription factor genes CncC and MafK. Silencing of either CncC or MafK reduced the expression of GSTe16, which exhibited the largest change in response to xanthotoxin. Additionally, analysis of the promoter sequence of GSTe16 revealed the presence of seven CncC/Maf binding sites. Luciferase reporter assays showed that CncC and MafK enhanced the expression of GSTe16, leading to the increased xanthotoxin tolerance in S. litura. These findings provide insight into the functions and transcriptional regulatory mechanisms of GSTes, thereby enhancing our understanding of the role of GSTs in the adaptation of lepidopteran pests to phytochemicals.

Transcriptional regulation and overexpression of GST cluster enhances pesticide resistance in the cotton bollworm, Helicoverpa armigera (Lepidoptera: Noctuidae)

The rapid evolution of resistance in agricultural pest poses a serious threat to global food security. However, the mechanisms of resistance through metabolic regulation are largely unknown. Here, we found that a GST gene cluster was strongly selected in North China (NTC) population, and it was significantly genetically-linked to lambda-cyhalothrin resistance. Knockout of the GST cluster using CRISPR/Cas9 significantly increased the sensitivity of the knockout strain to lambda-cyhalothrin. Haplotype analysis revealed no non-synonymous mutations or structural variations in the GST cluster, whereas GST_119 and GST_121 were significantly overexpressed in the NTC population. Silencing of GST_119 or co-silencing of GST_119 and GST_121 with RNAi significantly increased larval sensitivity to lambda-cyhalothrin. We also identified additional GATAe transcription factor binding sites in the promoter of NTC_GST_119. Transient expression of GATAe in Hi5 cells activated NTC_GST_119 and Xinjiang (XJ)_GST_119 transcription, but the transcriptional activity of NTC_GST_119 was significantly higher than that of XJ_GST_119. These results demonstrate that variations in the regulatory region result in complex expression changes in the GST cluster, which enhances lambda-cyhalothrin resistance in field-populations. This study deepens our knowledge of the evolutionary mechanism of pest adaptation under environmental stress and provides potential targets for monitoring pest resistance and integrated management.

Tissue-specific transcriptome analyses in Drosophila provide novel insights into the mode of action of the insecticide spinosad and the function of its target, nAChRα6

BACKGROUND

The insecticides spinosad and imidacloprid are neurotoxins with distinct modes of action. Both target nicotinic acetylcholine receptors (nAChRs), albeit different subunits. Spinosad is an allosteric modulator, that upon binding initiates endocytosis of its target, nAChRα6. Imidacloprid binding triggers excessive neuronal ion influx. Despite these differences, low-dose effects converge downstream in the precipitation of oxidative stress and neurodegeneration.

RESULTS

Using RNA-sequencing, we compared the transcriptional signatures of spinosad and imidacloprid, at low-dose exposures. Both insecticides cause up-regulation of glutathione S-transferase and cytochrome P450 genes in the brain and down-regulation in the fat body, whereas reduced expression of immune-related genes is observed in both tissues. Spinosad shows unique impacts on genes involved in lysosomal function, protein folding, and reproduction. Co-expression analyses revealed little to no correlation between genes affected by spinosad and nAChRα6 expressing neurons, but a positive correlation with glial cell markers. We also detected and experimentally confirmed nAChRα6 expression in fat body cells and male germline cells. This led us to uncover lysosomal dysfunction in the fat body following spinosad exposure, and a fitness cost in spinosad-resistant (nAChRα6 null) males - oxidative stress in testes, and reduced fertility.

CONCLUSION

Spinosad and imidacloprid share transcriptional perturbations in immunity-, energy homeostasis-, and oxidative stress-related genes. Low doses of other neurotoxic insecticides should be investigated for similar impacts. While target-site spinosad resistance mutation has evolved in the field, this may have a fitness cost. Our findings demonstrate the power of tissue-specific transcriptomics approach and the use of single-cell transcriptome data. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

The voltage-gated sodium channel, para, limits Anopheles coluzzii vector competence in a microbiota dependent manner

The voltage-gated sodium channel, para, is a target of DDT and pyrethroid class insecticides. Single nucleotide mutations in para, called knockdown resistant or kdr, which contribute to resistance against DDT and pyrethroid insecticides, have been correlated with increased susceptibility of Anopheles to the human malaria parasite Plasmodium falciparum. However, a direct role of para activity on Plasmodium infection has not yet been established. Here, using RNA-mediated silencing, we provide in vivo direct evidence for the requirement of wild-type (wt) para function for insecticide activity of deltamethrin. Depletion of wt para, which is susceptible to insecticide, causes deltamethrin tolerance, indicating that insecticide-resistant kdr alleles are likely phenocopies of loss of para function. We then show that normal para activity in An. coluzzii limits Plasmodium infection prevalence for both P. falciparum and P. berghei. A transcriptomic analysis revealed that para activity does not modulate the expression of immune genes. However, loss of para function led to enteric dysbiosis with a significant increase in the total bacterial abundance, and we show that para function limiting Plasmodium infection is microbiota dependent. In the context of the bidirectional "enteric microbiota-brain" axis studied in mammals, these results pave the way for studying whether the activity of the nervous system could control Anopheles vector competence.

Low concentration of indoxacarb interferes with the growth and development of silkworm by damaging the structure of midgut cells

As an important economic insect, Bombyx mori plays an essential role in the development of the agricultural economy. Indoxacarb, a novel sodium channel blocker insecticide, has been widely used for the control of various pests in agriculture and forestry, and its environmental pollution caused by flight control operations has seriously affected the safe production of sericulture in recent years. However, the lethal toxicity and adverse effects of indoxacarb on silkworm remain largely unknown. In this study, the toxicity of indoxacarb on the 5th instar larvae of silkworm was determined, with an LC50 (72 h) of 2.07 mg/L. Short-term exposure (24 h) to a low concentration of indoxacarb (1/2 LC50) showed significantly reduced body weight and survival rate of silkworm larvae. In addition, indoxacarb also led to decreased cocoon weight and cocoon shell weight, but had no significant effects on pupation, adult eclosion, and oviposition. Histopathological and ultrastructural analysis indicated that indoxacarb could severely damage the structure of the midgut epithelial cells, and lead to physiological impairment of the midgut. A total of 3883 differentially expressed genes (DEGs) were identified by midgut transcriptome sequencing and functionally annotated using GO and KEGG. Furthermore, the transcription level and enzyme activity of the detoxification related genes were determined, and our results suggested that esterases (ESTs) might play a major role in metabolism of indoxacarb in the midgut of B. mori. Future studies to examine the detoxification or biotransformation function of candidate genes will greatly enhance our understanding of indoxacarb metabolism in B. mori. The results of this study provide a theoretical basis for elucidating the mechanism of toxic effects of indoxacarb on silkworm by interfering with the normal physiological functions of the midgut.

Identifying potential insecticide resistance markers through genomic-level comparison of Bemisia tabaci (Gennadius) lines

The invasive whitefly (Bemisia tabaci) MED is one of the most economically damaging plant pests. The extensive use of insecticide over decades has led to that the invasive B. tabaci MED has developed resistance to a wide range of insecticide classes, but little is known about the genetic background associated with resistance. To this end, we conducted a comparative genome-wide analysis of single-base nucleotide polymorphisms between MED whitefly lines collected from fields that were recently infested and an insecticide-susceptible MED whitefly line collected in 1976. First, low-coverage genome sequencings were conducted on DNA isolated from individual whiteflies. The sequencing results were evaluated using an available B. tabaci MED genome as a reference. Significant genetic differences were discovered between MED whitefly lines collected from fields that were recently infested and an insecticide-susceptible MED whitefly line based on the principal component analyses. Top GO categories and KEGG pathways that might be involved in insecticide resistance development were identified, and several of them have not been previously associated with resistance. Additionally, we identified several genetic loci with novel variations including Cytochrome P450 monooxygenases (P450s), UDP-glucuronosyltransferases (UGTs), Glutathione S-transferases (GSTs), esterase, carboxyl-esterases (COE), ABC transporters, fatty acyl-CoA reductase, voltage-gated sodium channels, GABA receptor, and cuticle proteins (CPs) that were previously reported to have close associations with pesticide resistance in well-studied insect groups that provide an essential resource for the design of insecticide resistance-linked loci arrays insecticide. Our results was obtained solely on resequencing genome data sets, more pesticide bio-assays combined with omics datasets should be further used to verify the markers identified here.

Effects of different insecticides on transcripts of key genes in CncC pathway and detoxification genes in Helicoverpa armigera

The CncC pathway regulates the expression of multiple detoxification genes and contributes to the detoxification and antioxidation in insects. Many studies have focused on the impacts of plant allelochemicals on the CncC pathway, whereas studies on the effects of pesticides on key genes involved in this pathway are very limited. In this study, the effects of different types of commonly used insecticides on the transcripts of CncC, Keap1, and Maf and multiple detoxification genes of Helicoverpa armigera were evaluated using real-time quantitative polymerase chain reaction. The results showed that 8 insecticides (bifenthrin, λ-cyhalothrin, chlorantraniliprole, cyantraniliprole, spinosad, indoxacarb, chlorfenapyr, tolfenpyrad, and thiacloprid) significantly induced the expression of CncC and 4 insecticides (cypermethrin, acetamiprid, thiacloprid, and indoxacarb) suppressed the expression of Keap1 both at 24 h and 48 h; meanwhile, the expression levels of Maf were induced by 5 insecticides (fenvalerate, chlorantraniliprole, cyantraniliprole, lufenuron, and tolfenpyrad) at 24 h or 48 h. Multiple detoxification genes, especially cytochrome P450s genes, showed different up-regulation after bifenthrin, λ-cyhalothrin, chlorantraniliprole, cyantraniliprole, indoxacarb, and spinosad treatment for 48 h. Our results suggest that the CncC pathway and detoxification genes can be activated by different insecticides in H. armigera. These results establish a foundation for further studies on the relationship between the CncC pathway and the detoxification genes in H. armigera.

Recent insights into pesticide resistance mechanisms in Plutella xylostella and possible management strategies

Insects are incredibly successful and diverse organisms, but they also pose a significant threat to agricultural crops, causing potential losses of up to US$470 billion. Among these pests, Plutella xylostella (Linnaeus), a devastating insect that attacks cruciferous vegetables, alone results in monetary losses of around US$4-5 billion worldwide. While insecticides have effectively protected plants under field conditions, their use comes with various environmental and mammalian hazards. Additionally, insects are developing resistance to commonly used insecticides, rendering management strategies less effective. Arthropods employ a range of behavioral and biochemical mechanisms to cope with harmful chemicals, which contribute to the development of resistance. Understanding these mechanisms is crucial for addressing the issue of resistance. It is imperative to integrate strategies that can delay the development of resistance and enhance the efficiency of insecticides. Therefore, we present an overview of insecticide resistance in insects, focusing on P. xylostella, to provide insights into the current resistance status of this pest and propose tactics that can improve the effectiveness of insecticides.

Natural Coumarin Shows Toxicity to Spodoptera litura by Inhibiting Detoxification Enzymes and Glycometabolism

Coumarin and its derivatives are plant-derived compounds that exhibit potent insecticidal properties. In this study, we found that natural coumarin significantly inhibited the growth and development of Spodoptera litura larvae through toxicological assay. By transcriptomic sequencing, 80 and 45 differentially expressed genes (DEGs) related to detoxification were identified from 0 to 24 h and 24 to 48 h in S. litura after coumarin treatment, respectively. Enzyme activity analysis showed that CYP450 and acetylcholinesterase (AChE) activities significantly decreased at 48 h after coumarin treatment, while glutathione S-transferases (GST) activity increased at 24 h. Silencing of SlCYP324A16 gene by RNA interference significantly increased S. litura larval mortality and decreased individual weight after treatment with coumarin. Additionally, the expression levels of DEGs involved in glycolysis and tricarboxylic acid (TCA) cycle were inhibited at 24 h after coumarin treatment, while their expression levels were upregulated at 48 h. Furthermore, metabonomics analysis identified 391 differential metabolites involved in purine metabolism, amino acid metabolism, and TCA cycle from 0 to 24 h after treated with coumarin and 352 differential metabolites associated with ATP-binding cassette (ABC) transporters and amino acid metabolism. These results provide an in-depth understanding of the toxicological mechanism of coumarin on S. litura.

Genome-wide association studies reveal novel loci associated with pyrethroid and organophosphate resistance in Anopheles gambiae and Anopheles coluzzii

Resistance to insecticides in Anopheles mosquitoes threatens the effectiveness of malaria control, but the genetics of resistance are only partially understood. We performed a large scale multi-country genome-wide association study of resistance to two widely used insecticides: deltamethrin and pirimiphos-methyl, using sequencing data from An. gambiae and An. coluzzii from ten locations in West Africa. Resistance was highly multi-genic, multi-allelic and variable between populations. While the strongest and most consistent association with deltamethrin resistance came from Cyp6aa1, this was based on several independent copy number variants (CNVs) in An. coluzzii, and on a non-CNV haplotype in An. gambiae. For pirimiphos-methyl, signals included Ace1, cytochrome P450s, glutathione S-transferases and the nAChR target site of neonicotinoid insecticides. The regions around Cyp9k1 and the Tep family of immune genes showed evidence of cross-resistance to both insecticides. These locally-varying, multi-allelic patterns highlight the challenges involved in genomic monitoring of resistance, and may form the basis for improved surveillance methods.

Identification of metabolizing enzyme genes associated with xenobiotics and odorants in the predatory stink bug Arma custos based on transcriptome analysis

The predatory stink bug, Arma custos, is a highly effective beneficial predator of crop pests. The lack of gene information related to xenobiotic detoxification and odorant degrading enzymes in the predator stink bugs to date has limited our ability for more in-depth studies of biological control. Hence, we conducted de novo assembly of the A. custos transcriptome from guts, antennae, and other tiussue samples of 5th instar larvae using Illumina sequencing technology. A total of 91, 50 and 23 genes of cytochrome P450 monooxygenases (CYPs), carboxyl/choline esterases (CCEs) and glutathione S-transferases (GSTs) genes were identified, respectively. Gene expansions of CYP3 and CYP4 clans and the hormone and pheromone processing CCE class were found in A. custos. Analysis of tissue-specific expression patterns showed that 37 CYPs, 14 CCEs and 8 GSTs were enriched in guts, and 6 CYPs, 5 CCEs and 2 GSTs were up-regulated in antennae, suggesting their potential roles on xenobiotics detoxification and ordorant degradation. Gene information data presented here could be useful for a deeper understanding of the ecology, physiology and behavior of this beneficial species and could be helpful to improve their bio-control efficiency.

Identification and functional study of detoxification-related genes in response to tolfenpyrad stress in Glyphodes pyloalis Walker (Lepidoptera: Pyralidae)

Glyphodes pyloalis Walker (G. pyloalis) is a common destructive mulberry pest. Due to the long-term and frequent use of insecticides, it has developed tolerance to commonly used insecticides. Tolfenpyrad (TFP) is a novel pyrazole heterocyclic insecticide. In order to understand the TFP detoxification mechanism of G. pyloalis larvae, we first estimated the LC30 dose of TFP for 3rd instar G. pyloalis larvae. Next, we identified genes that were differentially expressed in 3rd instar G. pyloalis larvae treated with TFP compared to the control group by transcriptome sequencing. In total, 86,949,569 and 67,442,028 clean reads were obtained from TFP-treated and control G. pyloalis larvae, respectively. A total of 5588 differentially expressed genes (DEGs) were identified in TFP-treated and control G. pyloalis larvae, of which 3084 genes were upregulated and 2504 genes were downregulated. We analyzed the expression of 43 candidate detoxification enzyme genes associated with insecticide tolerance using qPCR. According to the spatiotemporal expression pattern of DEGs, we found that CYP6ABE1, CYP333A36 and GST-epsilon8 were highly expressed in the midgut, while CarEs14 was strongly expressed in haemolymph. Furthermore, we successfully knocked down these genes by RNA interference. After silencing CYP6ABE1 and CYP333A36, bioassay showed that the mortality rate of TFP-treated G. pyloalis larvae was significantly higher compared to the control group. This study provides a theoretical foundation for understanding the sensitivity of G. pyloalis to TFP and establish the basis for the effective and green management of this pest.

Comparative evolutionary analyses of eight whitefly Bemisia tabaci sensu lato genomes: cryptic species, agricultural pests and plant-virus vectors

BACKGROUND

The group of > 40 cryptic whitefly species called Bemisia tabaci sensu lato are amongst the world's worst agricultural pests and plant-virus vectors. Outbreaks of B. tabaci s.l. and the associated plant-virus diseases continue to contribute to global food insecurity and social instability, particularly in sub-Saharan Africa and Asia. Published B. tabaci s.l. genomes have limited use for studying African cassava B. tabaci SSA1 species, due to the high genetic divergences between them. Genomic annotations presented here were performed using the 'Ensembl gene annotation system', to ensure that comparative analyses and conclusions reflect biological differences, as opposed to arising from different methodologies underpinning transcript model identification.

RESULTS

We present here six new B. tabaci s.l. genomes from Africa and Asia, and two re-annotated previously published genomes, to provide evolutionary insights into these globally distributed pests. Genome sizes ranged between 616-658 Mb and exhibited some of the highest coverage of transposable elements reported within Arthropoda. Many fewer total protein coding genes (PCG) were recovered compared to the previously published B. tabaci s.l. genomes and structural annotations generated via the uniform methodology strongly supported a repertoire of between 12.8-13.2 × 10³ PCG. An integrative systematics approach incorporating phylogenomic analysis of nuclear and mitochondrial markers supported a monophyletic Aleyrodidae and the basal positioning of B. tabaci Uganda-1 to the sub-Saharan group of species. Reciprocal cross-mating data and the co-cladogenesis pattern of the primary obligate endosymbiont 'Candidatus Portiera aleyrodidarum' from 11 Bemisia genomes further supported the phylogenetic reconstruction to show that African cassava B. tabaci populations consist of just three biological species. We include comparative analyses of gene families related to detoxification, sugar metabolism, vector competency and evaluate the presence and function of horizontally transferred genes, essential for understanding the evolution and unique biology of constituent B. tabaci. s.l species.

CONCLUSIONS

These genomic resources have provided new and critical insights into the genetics underlying B. tabaci s.l. biology. They also provide a rich foundation for post-genomic research, including the selection of candidate gene-targets for innovative whitefly and virus-control strategies.

Identification and Characterization of Glutathione S-transferase Genes in Spodoptera frugiperda (Lepidoptera: Noctuidae) under Insecticides Stress

Insect glutathione S-transferases (GSTs) serve critical roles in insecticides and other forms of xenobiotic chemical detoxification. The fall armyworm, Spodoptera frugiperda (J. E. Smith), is a major agricultural pest in several countries, especially Egypt. This is the first study to identify and characterize GST genes in S. frugiperda under insecticidal stress. The present work evaluated the toxicity of emamectin benzoate (EBZ) and chlorantraniliprole (CHP) against the third-instar larvae of S. frugiperda using the leaf disk method. The LC₅₀ values of EBZ and CHP were 0.029 and 1.250 mg/L after 24 h of exposure. Moreover, we identified 31 GST genes, including 28 cytosolic and 3 microsomal SfGSTs from a transcriptome analysis and the genome data of S. frugiperda. Depending on the phylogenetic analysis, sfGSTs were divided into six classes (delta, epsilon, omega, sigma, theta, and microsomal). Furthermore, we investigated the mRNA levels of 28 GST genes using qRT-PCR under EBZ and CHP stress in the third-instar larvae of S. frugiperda. Interestingly, SfGSTe10 and SfGSTe13 stood out with the highest expression after the EBZ and CHP treatments. Finally, a molecular docking model was constructed between EBZ and CHP using the most upregulated genes (SfGSTe10 and SfGSTe13) and the least upregulated genes (SfGSTs1 and SfGSTe2) of S. frugiperda larvae. The molecular docking study showed EBZ and CHP have a high binding affinity with SfGSTe10, with docking energy values of -24.41 and -26.72 kcal/mol, respectively, and sfGSTe13, with docking energy values of -26.85 and -26.78 kcal/mol, respectively. Our findings are important for understanding the role of GSTs in S. frugiperda regarding detoxification processes for EBZ and CHP.

Genome-Wide Identification of Detoxification Genes in Wild Silkworm Antheraea pernyi and Transcriptional Response to Coumaphos

For a half-century, the commercial wild silkworm, Antheraea pernyi, has been protected by coumaphos, which is an internal organophosphorus insecticide used to kill the potential parasitic fly larvae inside. Knowledge about the detoxification genes of A. pernyi as well as the detoxification mechanism for this species remains severely limited. In this study, we identified 281 detoxification genes (32 GSTs, 48 ABCs, 104 CYPs, and 97 COEs) in the genome of this insect, which are unevenly distributed over 46 chromosomes. When compared to the domesticated silkworm, Bombyx mori, a lepidopteran model species, A. pernyi has a similar number of ABCs, but a greater number of GSTs, CYPs, and COEs. By transcriptome-based expression analysis, we found that coumaphos at a safe concentration level significantly changed the pathways related to ATPase complex function and the transporter complex in A. pernyi. KEGG functional enrichment analysis indicated that protein processing in the endoplasmic reticulum was the most affected pathway after coumaphos treatment. Finally, we identified four significantly up-regulated detoxification genes (ABCB1, ABCB3, ABCG11, and ae43) and one significantly down-regulated detoxification gene (CYP6AE9) in response to coumaphos treatment, suggesting that these five genes may contribute to detoxification of coumaphos in A. pernyi. Our study provides the first set of detoxification genes for wild silkworms from Saturniidae and highlights the importance of detoxification gene repertoire in insect pesticide tolerance.

Susceptibility monitoring and comparative gene expression of susceptible and resistant strains of Spodoptera frugiperda to lambda-cyhalothrin and chlorpyrifos

BACKGROUND

Spodoptera frugiperda (J. E. Smith) is a widespread agricultural pest with several records of resistance to different insecticides and Bt proteins, including the neurotoxic insecticides chlorpyrifos (organophosphate) and lambda-cyhalothrin (pyrethroid). Here, we (i) characterized and monitored the susceptibility of field populations of S. frugiperda to chlorpyrifos (194 populations) and lambda-cyhalothrin (197 populations) collected from major maize-growing regions of Brazil from 2003 to 2016, and (ii) compared gene expression levels of laboratory-selected, chlorpyrifos- and lambda-cyhalothrin-resistant strains to a susceptible reference strain (Sf-ss) of S. frugiperda.

RESULTS

The susceptibility monitoring detected average survival ranging from 29.3% to 36.0% for chlorpyrifos, and 23.1% to 68.0% for lambda-cyhalothrin. The resistance ratio of the chlorpyrifos-resistant strain (Clo-rr) was 25.4-fold and of the lambda-cyhalothrin-resistant strain (Lam-rr) was 21.5-fold. We identified 1098 differentially expressed genes (DEGs) between Clo-rr and Sf-ss, and 303 DEGs between Lam-rr and Sf-ss. Functional analyses of the DEGs revealed the up-regulation of several detoxification enzymes, mainly cytochrome P450 belonging to CYP3 and CYP6 clans. Genes associated with regulatory processes, such as the forkhead box class O (FoxO) transcription factor were also up-regulated. Variant analysis of target-site mutations for both pesticides identified the A201S and F290V mutations in acetylcholinesterase-1, both occurring in heterozigosis in the Clo-rr S. frugiperda strain.

CONCLUSION

Our data show that the overexpression of the enzymatic detoxification machinery is the main difference to explain the resistance of Clo-rr and Lam-rr strains of S. frugiperda to chlorpyrifos and lambda-cyhalothrin, although a target-site mutation also contributes to the Clo-rr resistance to chlorpyrifos. © 2023 Society of Chemical Industry.

Glutathione S-Transferase Highly Expressed in Holotrichia parallela Antennae Inactivates the Odorant Unsaturated Aldehyde Volatiles

Odorant-degrading enzymes in insects play a vital role in maintaining olfactory sensitivity. However, the role and molecular mechanism of glutathione S-transferases (GSTs) in odorant inactivation has been rarely studied. In the present study, 31 GSTs were identified from the antennal transcriptome of Holotrichia parallela. HpGSTd1 possesses the highest transcriptome expression level. Recombinant HpGSTd1 showed degradation activity toward various unsaturated aldehyde volatiles. Furthermore, the metabolite of cinnamaldehyde was identified by high-resolution mass spectrometry (HRMS). The molecular docking analysis and site-directed mutagenesis revealed the key residues of HpGSTd1 in degrading odorants. In addition, the unsaturated aldehyde volatiles elicited the behavioral and electrophysiological responses of H. parallela. Taken together, our findings suggest that HpGSTd1 may play an essential role in inactivating odorants in H. parallela, which provides new insights for identifying molecular targets and exploring effective olfactory regulators for this underground pest.

Expression profile of the entire detoxification gene inventory of the western honeybee, Apis mellifera across life stages

The western honeybee, Apis mellifera, is a managed pollinator of many crops and potentially exposed to a wide range of foreign compounds, including pesticides throughout its life cycle. Honeybees as well as other insects recruit molecular defense mechanisms to facilitate the detoxification of xenobiotic compounds. The inventory of detoxification genes (DETOXome) is comprised of five protein superfamilies: cytochrome P450 monooxygenases (P450), carboxylesterases, glutathione S-transferases (GST), UDP-glycosyl transferases (UGT) and ATP-binding cassette (ABC) transporters. Here we characterized the gene expression profile of the entire honeybee DETOXome by analyzing 47 transcriptomes across the honeybee life cycle, including different larval instars, pupae, and adults. All life stages were well separated by principal component analysis, and K-means clustering revealed distinct temporal patterns of gene expression. Indeed, >50% of the honeybee detoxification gene inventory is found in one cluster and follows strikingly similar expression profiles, i.e., increased expression during larval development, followed by a sharp decline after pupation and a steep increase again in adults. This cluster includes 29 P450 genes dominated by CYP3 and CYP4 clan members, 15 ABC transporter genes mostly belonging to the ABCC subfamily and 13 carboxylesterase genes including almost all members involved in dietary/detox and hormone/semiochemical processing. RT-qPCR analysis of selected detoxification genes from all families revealed high expression levels in various tissues, especially Malpighian tubules, fatbody and midgut, supporting the view that these tissues are essential for metabolic clearance of environmental toxins and pollutants in honeybees. Our study is meant to spark further research on the molecular basis of detoxification in this critical pollinator to better understand and evaluate negative impacts from potentially toxic substances. Additionally, the entire gene set of 47 transcriptomes collected and analyzed provides a valuable resource for future honeybee research across different disciplines.

Recombinant expression and characterization of GSTd3 from a resistant population of Anopheles arabiensis and comparison of DDTase activity with GSTe2

The development of insecticide resistance in malaria vectors is a challenge for the global effort to control and eradicate malaria. Glutathione S-transferases (GSTs) are multifunctional enzymes involved in the detoxification of many classes of insecticides. For mosquitoes, it is known that overexpression of an epsilon GST, GSTe2, confers resistance towards DDT and pyrethroids. In addition to GSTe2, consistent overexpression of a delta class GST, GSTd3, has been observed in insecticide resistant populations of different malaria vector species. However, the functional role of GSTd3 towards DDT resistance has not yet been investigated. Here, we recombinantly expressed both GSTe2 and GSTd3 from Anopheles arabiensis and compared their metabolic activities against DDT. Both AaGSTd3 and AaGSTe2 exhibited CDNB-conjugating and glutathione peroxidase activity and DDT metabolism was observed for both GSTs. However, the DDT dehydrochlorinase activity exhibited by AaGSTe2 was much higher than for AaGSTd3, and AaGSTe2 was also able to eliminate DDE although the metabolite could not be identified. Molecular modeling revealed subtle differences in the binding pocket of both enzymes and a better fit of DDT within the H-site of AaGSTe2. The overexpression but much lower DDT metabolic activity of AaGSTd3, might suggest that AaGSTd3 sequesters DDT. These findings highlight the complexity of insecticide resistance in the major malaria vectors and the difficulties associated with control of the vectors using DDT, which is still used for indoor residual spraying.

The buzz in the field: the interaction between viruses, mosquitoes, and metabolism

Among many medically important pathogens, arboviruses like dengue, Zika and chikungunya cause severe health and economic burdens especially in developing countries. These viruses are primarily vectored by mosquitoes. Having surmounted geographical barriers and threat of control strategies, these vectors continue to conquer many areas of the globe exposing more than half of the world's population to these viruses. Unfortunately, no medical interventions have been capable so far to produce successful vaccines or antivirals against many of these viruses. Thus, vector control remains the fundamental strategy to prevent disease transmission. The long-established understanding regarding the replication of these viruses is that they reshape both human and mosquito host cellular membranes upon infection for their replicative benefit. This leads to or is a result of significant alterations in lipid metabolism. Metabolism involves complex chemical reactions in the body that are essential for general physiological functions and survival of an organism. Finely tuned metabolic homeostases are maintained in healthy organisms. However, a simple stimulus like a viral infection can alter this homeostatic landscape driving considerable phenotypic change. Better comprehension of these mechanisms can serve as innovative control strategies against these vectors and viruses. Here, we review the metabolic basis of fundamental mosquito biology and virus-vector interactions. The cited work provides compelling evidence that targeting metabolism can be a paradigm shift and provide potent tools for vector control as well as tools to answer many unresolved questions and gaps in the field of arbovirology.

Genome-wide analyses of Glutathione S-transferase gene family and expression profiling under deltamethrin exposure in non-biting midge Propsilocerus akamusi

Glutathione S-transferases (GSTs) are major enzymes in detoxification phase II, and have been functioned in resistance to various insecticides or oxidative stress. Herein, we selected the non-biting midge, Propsilocerus akamusi, widespread in Asian aquatic ecosystems, to uncover the gene location, structure, and phylogenetics relationship of GSTs at genome scale first time. Thirty-three cytosolic and four microsomal GST genes were identified and located on the four chromosomes. The cytosolic GSTs involved in the eight subclasses and five GST genes were unclassified. The expansion of GST genes in P. akamusi experienced duplication events on the delta, theta, xi, iota, and unclassified subclasses. The RNA-Seq analyses and RT-qPCR validation showed that the expression of PaGSTt2 gene is significantly elevated, with deltamethrin concentration increasing. The tertiary structure of PaGSTt2 enzyme was reconstructed, which was different from the other theta gene in the active site. In addition, the GST genes of six chironomids were first described based on the assembled genomes to explore the difference of those in the adaptation to kinds of environments. The GST frame for P. akmusi and its expression profiles provide valuable resources to understand their role in insecticide resistance of this species, as well as those of other biting midges.

Effects of oral exposure to brake wear particulate matter on the springtail Orthonychiurus folsomi

Most of the heavy metals in urban environments derives from road traffic, particularly from tyres and brake wear (non-exhaust emission sources). These pollutants contaminate the soil, where several organisms have a primary ecosystem role (e.g., springtails, ants, earthworms). Springtails (Collembola) are soil-dwelling animals regulating soil fertility, flow of energy through above- and below-ground food webs, and they contribute to soil microbial community dispersion and biodiversity maintenance. In this study we investigated the ecotoxicological effects of oral exposure to particles emitted from brake pads and cast-iron brake discs in the euedaphic collembola species Orthonychiurus folsomi under laboratory conditions. Our results showed that chronic exposure to brake wear particles can have sub-lethal effects both at low and high concentrations and it can cause histological alterations. Here, SEM-EDX was applied to observe the particulate and we found its chemical markers in the gut and faeces of collembola, while histological analysis detected alterations of the digestive and reproductive systems and of the abdominal fat body at high concentrations.

Strong Positive Selection in Aedes aegypti and the Rapid Evolution of Insecticide Resistance

Aedes aegypti vectors the pathogens that cause dengue, yellow fever, Zika virus, and chikungunya and is a serious threat to public health in tropical regions. Decades of work has illuminated many aspects of Ae. aegypti's biology and global population structure and has identified insecticide resistance genes; however, the size and repetitive nature of the Ae. aegypti genome have limited our ability to detect positive selection in this mosquito. Combining new whole genome sequences from Colombia with publicly available data from Africa and the Americas, we identify multiple strong candidate selective sweeps in Ae. aegypti, many of which overlap genes linked to or implicated in insecticide resistance. We examine the voltage-gated sodium channel gene in three American cohorts and find evidence for successive selective sweeps in Colombia. The most recent sweep encompasses an intermediate-frequency haplotype containing four candidate insecticide resistance mutations that are in near-perfect linkage disequilibrium with one another in the Colombian sample. We hypothesize that this haplotype may continue to rapidly increase in frequency and perhaps spread geographically in the coming years. These results extend our knowledge of how insecticide resistance has evolved in this species and add to a growing body of evidence suggesting that Ae. aegypti has an extensive genomic capacity to rapidly adapt to insecticide-based vector control.

The genetic basis of adaptation to copper pollution in Drosophila melanogaster

Introduction: Heavy metal pollutants can have long lasting negative impacts on ecosystem health and can shape the evolution of species. The persistent and ubiquitous nature of heavy metal pollution provides an opportunity to characterize the genetic mechanisms that contribute to metal resistance in natural populations. Methods: We examined variation in resistance to copper, a common heavy metal contaminant, using wild collections of the model organism Drosophila melanogaster. Flies were collected from multiple sites that varied in copper contamination risk. We characterized phenotypic variation in copper resistance within and among populations using bulked segregant analysis to identify regions of the genome that contribute to copper resistance. Results and Discussion: Copper resistance varied among wild populations with a clear correspondence between resistance level and historical exposure to copper. We identified 288 SNPs distributed across the genome associated with copper resistance. Many SNPs had population-specific effects, but some had consistent effects on copper resistance in all populations. Significant SNPs map to several novel candidate genes involved in refolding disrupted proteins, energy production, and mitochondrial function. We also identified one SNP with consistent effects on copper resistance in all populations near CG11825, a gene involved in copper homeostasis and copper resistance. We compared the genetic signatures of copper resistance in the wild-derived populations to genetic control of copper resistance in the Drosophila Synthetic Population Resource (DSPR) and the Drosophila Genetic Reference Panel (DGRP), two copper-naïve laboratory populations. In addition to CG11825, which was identified as a candidate gene in the wild-derived populations and previously in the DSPR, there was modest overlap of copper-associated SNPs between the wild-derived populations and laboratory populations. Thirty-one SNPs associated with copper resistance in wild-derived populations fell within regions of the genome that were associated with copper resistance in the DSPR in a prior study. Collectively, our results demonstrate that the genetic control of copper resistance is highly polygenic, and that several loci can be clearly linked to genes involved in heavy metal toxicity response. The mixture of parallel and population-specific SNPs points to a complex interplay between genetic background and the selection regime that modifies the effects of genetic variation on copper resistance.

Antioxidant availability trades off with warning signals and toxin sequestration in the large milkweed bug (Oncopeltus fasciatus)

In some aposematic species the conspicuousness of an individual's warning signal and the concentration of its chemical defense are positively correlated. Several mechanisms have been proposed to explain this phenomenon, including resource allocation trade-offs where the same limiting resource is needed to produce both the warning signal and chemical defense. Here, the large milkweed bug (Oncopeltus fasciatus: Heteroptera, Lygaeinae) was used to test whether allocation of antioxidants, that can impart color, trade against their availability to prevent self-damage caused by toxin sequestration. We investigated if (i) the sequestration of cardenolides is associated with costs in the form of changes in oxidative state; and (ii) oxidative state can affect the capacity of individuals to produce warning signals. We reared milkweed bugs on artificial diets with increasing quantities of cardenolides and examined how this affected signal quality (brightness and chroma) across different instars. We then related the expression of warning colors to the quantity of sequestered cardenolides and indicators of oxidative state-oxidative lipid damage (malondialdehyde), and two antioxidants: total superoxide dismutase and total glutathione. Bugs that sequestered more cardenolides had significantly lower levels of the antioxidant glutathione, and bugs with less total glutathione had less luminant orange warning signals and reduced chroma of their black patches compared to bugs with more glutathione. Bugs that sequestered more cardenolides also had reduced red-green chroma of their black patches that was unrelated to oxidative state. Our results give tentative support for a physiological cost of sequestration in milkweed bugs and a mechanistic link between antioxidant availability, sequestration, and warning signals.

The effects of short-term glyphosate-based herbicide exposure on insect gene expression profiles

Glyphosate-based herbicides (GBHs) are the most frequently used herbicides worldwide. The use of GBHs is intended to tackle weeds, but GBHs have been shown to affect the life-history traits and antioxidant defense system of invertebrates found in agroecosystems. Thus far, the effects of GBHs on detoxification pathways among invertebrates have not been sufficiently investigated. We performed two different experiments-1) the direct pure glyphosate and GBH treatment, and 2) the indirect GBH experiment via food-to examine the possible effects of environmentally relevant GBH levels on the survival of the Colorado potato beetle (Leptinotarsa decemlineata) and the expression profiles of their detoxification genes. As candidate genes, we selected four cytochrome P450 (CYP), three glutathione-S-transferase (GST), and two acetylcholinesterase (AChE) genes that are known to be related to metabolic or target-site resistances in insects. We showed that environmentally relevant levels of pure glyphosate and GBH increased the probability for higher mortality in the Colorado potato beetle larvae in the direct experiment, but not in the indirect experiment. The GBHs or glyphosate did not affect the expression profiles of the studied CYP, GST, or AChE genes; however, we found a large family-level variation in expression profiles in both the direct and indirect treatment experiments. These results suggest that the genes selected for this study may not be the ones expressed in response to glyphosate or GBHs. It is also possible that the relatively short exposure time did not affect gene expression profiles, or the response may have already occurred at a shorter exposure time. Our results show that glyphosate products may affect the survival of the herbivorous insect already at lower levels, depending on their sensitivity to pesticides.

Synergistic effects of chlorantraniliprole and camptothecin on physiological impairments, histopathological, biochemical changes, and genes responses in the larvae midgut of Spodoptera frugiperda

Spodoptera frugiperda is an economically important agricultural pest and poses a serious threat to food security globally. Its management is gravely challenged by its high polyphagous nature, strong migratory ability, and massive fecundity. Chlorantraniliprole (CHL) is widely utilized in controlling S. frugiperda, its intensive application and over-reliance pose adverse health risks, development of resistance, toxicity to beneficial insects, natural enemies, and environmental contamination. To address S. frugiperda resistance to CHL and its inherent challenges, this study explores the synergistic effects of camptothecin (CPT) with CHL in its management. The binary mixed adversely induced the larvae weight and mortality when compared to single-treated. CHL + CPT (1:20 mg/L) had the highest larvae mortality of (73.80 %) with a high antagonistic factor (0.90), while (1:10 mg/L) with (66.10%) mortality exhibited a high synergistic factor (1.43). Further, CHL + CPT (1:10 mg/L) considerably altered the midgut epithelial cell, peritrophic membrane, microvilli, basement membrane, and regenerative cells. For biochemical analysis, CHL + CPT (1:10 mg/L) significantly decreased glutathione-S-transferase (1-chloro-2,4-dinitrobenzene CDNB) and cytochrome P450 (7-ethoxycoumarin O-deethylation) activities in the midgut in a dose and time dependent manner. Based on RNA-Seq analysis, a total of 4,373 differentially expressed genes (DEGs) were identified from the three treatments. CPT vs CK (Control) had 1694 (968 up-, 726 down-regulated), CHL vs CK with 1771 (978 up-, 793 down-regulated), and CHL + CPT vs CK had 908 (394 up-, 514 down-regulated) DEGs. The enrichment analysis disclosed significant pathways such as metabolism of xenobiotics by cytochrome P450, glutathione metabolism, TOLL and IMD (Immune Deficiency) signaling pathway, longevity regulating pathway. This study provides basis to expatiate on the molecular toxicological mechanism of CHL + CPT in management of fall armyworm.

Genome-Wide Identification and Expression Profiling of Glutathione S-Transferase Gene Family in Foxtail Millet (Setaria italica L.)

Glutathione S-transferases (GSTs) are a critical superfamily of multifunctional enzymes in plants. As a ligand or binding protein, GSTs regulate plant growth and development and detoxification. Foxtail millet (Setaria italica (L.) P. Beauv) could respond to abiotic stresses through a highly complex multi-gene regulatory network in which the GST family is also involved. However, GST genes have been scarcely studied in foxtail millet. Genome-wide identification and expression characteristics analysis of the foxtail millet GST gene family were conducted by biological information technology. The results showed that 73 GST genes (SiGSTs) were identified in the foxtail millet genome and were divided into seven classes. The chromosome localization results showed uneven distribution of GSTs on the seven chromosomes. There were 30 tandem duplication gene pairs belonging to 11 clusters. Only one pair of SiGSTU1 and SiGSTU23 were identified as fragment duplication genes. A total of ten conserved motifs were identified in the GST family of foxtail millet. The gene structure of SiGSTs is relatively conservative, but the number and length of exons of each gene are still different. The cis-acting elements in the promoter region of 73 SiGST genes showed that 94.5% of SiGST genes possessed defense and stress-responsive elements. The expression profiles of 37 SiGST genes covering 21 tissues suggested that most SiGST genes were expressed in multiple organs and were highly expressed in roots and leaves. By qPCR analysis, we found that 21 SiGST genes were responsive to abiotic stresses and abscisic acid (ABA). Taken together, this study provides a theoretical basis for identifying foxtail millet GST family information and improving their responses to different stresses.