Metabolism of imidacloprid and DDT by P450 CYP6G1 expressed in cell cultures of Nicotiana tabacum suggests detoxification of these insecticides in Cyp6g1-overexpressing strains of Drosophila melanogaster, leading to resistance

Short-term fasting of a single amino acid extends lifespan

Diet and health are strongly linked, though the strict changes in diet required to improve health outcomes are usually difficult to sustain. We sought to understand whether short-term bouts of amino acid-specific modifications to the diet of Drosophila melanogaster could mimic the lifespan and stress resistance benefits of dietary restriction, without the requirement for drastic reductions in food intake. We found that flies that were transiently fed diets lacking the essential amino acid isoleucine, but otherwise nutritionally complete, exhibited enhanced nicotine tolerance, indicating elevated detoxification capacity. The protection from isoleucine deprivation increased with the duration of exposure, up to a maximum at 7-day isoleucine deprivation for flies 2, 3, or 4 weeks of age, and a 5-day deprivation when flies were 5 weeks of age. Because of these beneficial effects on toxin resistance, we intermittently deprived flies of isoleucine during the first 6 weeks of adulthood and monitored the effect on lifespan. Lifespan was significantly extended when flies experienced short-term isoleucine deprivation at 3 and 5 weeks of age, regardless of whether they were also deprived at 1 week. These results indicate that short-term bouts of isoleucine deprivation can extend lifespan and highlight its cumulative and time-dependent benefits. Interestingly, we found that isoleucine-deprived flies lost their protection against nicotine within 3 days of returning to fully fed conditions. Therefore, the mechanisms underlying lifespan extension may involve transient damage clearance during the bouts of isoleucine deprivation rather than sustained enhanced detoxification capacity. These data highlight a new time-restricted, nutritionally precise method to extend life in Drosophila melanogaster and point to a more manageable dietary method to combat ageing.

Transiently restricting individual amino acids protects Drosophila melanogaster against multiple stressors

Nutrition and resilience are linked, though it is not yet clear how diet confers stress resistance or the breadth of stressors that it can protect against. We have previously shown that transiently restricting an essential amino acid can protect Drosophila melanogaster against nicotine poisoning. Here, we sought to characterize the nature of this dietary-mediated protection and determine whether it was sex, amino acid and/or nicotine specific. When we compared between sexes, we found that isoleucine deprivation increases female, but not male, nicotine resistance. Surprisingly, we found that this protection afforded to females was not replicated by dietary protein restriction and was instead specific to individual amino acid restriction. To understand whether these beneficial effects of diet were specific to nicotine or were generalizable across stressors, we pre-treated flies with amino acid restriction diets and exposed them to other types of stress. We found that some of the diets that protected against nicotine also protected against oxidative and starvation stress, and improved survival following cold shock. Interestingly, we found that a diet lacking isoleucine was the only diet to protect against all these stressors. These data point to isoleucine as a critical determinant of robustness in the face of environmental challenges.

Burning question: Rethinking organohalide degradation strategy for bioremediation applications

Organohalides are widespread pollutants that pose significant environmental hazards due to their high degree of halogenation and elevated redox potentials, making them resistant to natural attenuation. Traditional bioremediation approaches, primarily relying on bioaugmentation and biostimulation, often fall short of achieving complete detoxification. Furthermore, the emergence of complex halogenated pollutants, such as per- and polyfluoroalkyl substances (PFASs), further complicates remediation efforts. Therefore, there is a pressing need to reconsider novel approaches for more efficient remediation of these recalcitrant pollutants. This review proposes novel redox-potential-mediated hybrid bioprocesses, tailored to the physicochemical properties of pollutants and their environmental contexts, to achieve complete detoxification of organohalides. The possible scenarios for the proposed bioremediation approaches are further discussed. In anaerobic environments, such as sediment and groundwater, microbial reductive dehalogenation coupled with fermentation and methanogenesis can convert organohalides into carbon dioxide and methane. In environments with anaerobic-aerobic alternation, such as paddy soil and wetlands, a synergistic process involving reduction and oxidation can facilitate the complete mineralization of highly halogenated organic compounds. Future research should focus on in-depth exploration of microbial consortia, the application of ecological principles-guided strategies, and the development of bioinspired-designed techniques. This paper contributes to the academic discourse by proposing innovative remediation strategies tailored to the complexities of organohalide pollution.

Sesamin Exerts an Antioxidative Effect by Activating the Nrf2 Transcription Factor in the Glial Cells of the Central Nervous System in Drosophila Larvae

Sesame seeds are abundant in sesamin, which exerts health-promoting effects such as extending the lifespan of adult Drosophila and suppressing oxidative stress by activating the Nrf2 transcription factor. Here, we investigated whether sesamin activated Nrf2 in larval tissues and induced the expression of Nrf2 target genes. In the sesamin-fed larvae, Nrf2 was activated in the central nervous system (CNS), gut, and salivary glands. The ectopic expression of Keap1 in glial cells inhibited sesamin-induced Nrf2 activation in the whole CNS more than in the neurons, indicating that sesamin activates Nrf2 in glia efficiently. We labeled the astrocytes as well as cortex and surface glia with fluorescence to identify the glial cell types in which Nrf2 was activated; we observed their activation in both cell types. These data suggest that sesamin may stimulate the expression of antioxidative genes in glial cells. Among the 17 candidate Nrf2 targets, the mRNA levels of Cyp6a2 and Cyp6g1 in cytochrome P450 were elevated in the CNS, gut, and salivary glands of the sesamin-fed larvae. However, this elevation did not lead to resistance against imidacloprid, which is detoxified by these enzymes. Our results suggest that sesamin may exert similar health-promoting effects on the human CNS and digestive tissues.

Transcription factors, cap 'n' collar isoform C regulates the expression of CYP450 genes involving in insecticides susceptibility in Locusta migratoria

BACKGROUND

The cap 'n' collar (Cnc) belongs to the Basic Leucine Zipper (bZIP) transcription factor super family. Cap 'n' collar isoform C (CncC) is highly conserved in the animal kingdom. CncC contributes to the regulation of growth, development, and aging and takes part in the maintenance of homeostasis and the defense against endogenous and environmental stress. Insect CncC participates in the regulation of various kinds of stress-responsive genes and is involved in the development of insecticide resistance.

RESULTS

In this study, one full-length CncC sequence of Locusta migratoria was identified and characterized. Upon RNAi silencing of LmCncC, insecticide bioassays showed that LmCncC played an essential role in deltamethrin and imidacloprid susceptibility. To fully investigate the downstream genes regulated by LmCncC and further identify the LmCncC-regulated genes involved in deltamethrin and imidacloprid susceptibility, a comparative transcriptome was constructed. Thirty-five up-regulated genes and 73 down-regulated genes were screened from dsLmCncC-knockdown individuals. We selected 22 LmCncC-regulated genes and verified their gene expression levels using RT-qPCR. Finally, six LmCYP450 genes belonging to the CYP6 family were selected as candidate detoxification genes, and LmCYP6FD1 and LmCYP6FE1 were further validated as detoxification genes of insecticides via RNAi, insecticide bioassays, and metabolite identification.

CONCLUSIONS

Our data suggest that the locust CncC gene is associated with deltamethrin and imidacloprid susceptibility via the regulation of LmCYP6FD1 and LmCYP6FE1, respectively.

Functional characterization of cytochrome P450s associated with pyrethroid resistance in the olive fruit fly Bactrocera oleae

Resistance to pyrethroid insecticides has evolved in Bactrocera oleae populations in Greece, threatening the efficacy of control interventions based on this insecticide class. Here we report the collection of populations from Crete, with resistance levels reaching up to 132-folds, compared to susceptible laboratory strains and show that pyrethroid resistance is substantially suppressed by the PBO synergist, suggesting the involvement of detoxification enzymes. To identify specific candidate genes implicated in resistance, we performed comparative transcriptomic analysis, between the pyrethroid resistant populations from Crete and the susceptible laboratory strains, using both whole bodies and Malpighian tubules. Several genes were found differentially transcribed between resistant and susceptible flies in each comparison, with P450s being among the most highly over-expressed detoxification genes in pyrethroid resistant populations. Four of the over-expressed P450s (Cyp6A61, Cyp6G6, Cyp4P6 and Cyp6G28) were recombinantly expressed in Escherichia coli and in vitro metabolism assays revealed that CYP6A61 is capable of metabolizing alpha-cypermethrin, while CYP6G6, CYP4P6 and CYP6G28 are capable of metabolizing deltamethrin. No metabolism of neonicotinoid insecticides was recorded. We further silenced CYP6G6 in vivo, via RNAi, which led to a small, but significant increase in deltamethrin toxicity. The study provides valuable information towards the development of molecular diagnostics and evidence-based insecticide resistance management strategies.

Expression profile of CYP402C1 and its role in resistance to imidacloprid in the whitefly, Bemisia tabaci

Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) is a cosmopolitan insect pest causing serious damage to crop production. Cytochromes P450 (CYPs) of B. tabaci are widely known to be involved in the metabolic resistance to a variety of insecticides, continuously increasing the difficulty in controlling this pest. In this study, four P450 genes (CYP6CM1, CYP6CX1, CYP6CX3, and CYP402C1) in B. tabaci exhibited correlations with the resistance to imidacloprid. We have focused on trying to understand the function and metabolism capacity of CYP402C1. The expression profiles of CYP402C1 were examined by reverse transcription quantitative real-time PCR and fluorescence in situ hybridizations. Its role in resistance to imidacloprid was investigated by RNA interference, transgenic Drosophila melanogaster, and heterologous expression. The results showed that CYP402C1 was highly expressed in the active feeding stages of B. tabaci, such as nymphs and female adults. CYP402C1 was mainly expressed in midguts of nymphs and adults, especially in the filter chamber. Knockdown of CYP402C1 significantly decreased the resistance of B. tabaci to imidacloprid by 3.96-fold (50% lethal concentration: 186.46 versus 47.08 mg/L). Overexpression of CYP402C1 in a transgenic D. melanogaster line (Gal4 > UAS-CYP402C1) significantly increased the resistance to imidacloprid from 12.68- to 14.92-fold (129.01 and 151.80 mg/L versus 1925.14 mg/L). The heterologous expression of CYP402C1 showed a metabolism ability of imidacloprid (imidacloprid decreased by 12.51% within 2 h). This study provides new insights for CYP402C1 function in B. tabaci and will help develop new strategies in B. tabaci control and its insecticide resistance.

What does not kill it makes it stronger! The tolerance of the F1 larvae of Chironomus xanthus to a neonicotinoid insecticide formulation

Thiamethoxam (TMX) is a systemic neonicotinoid that acts as a partial agonist of the nicotinic acetylcholine receptors (nAChRs). However, target species have shown resistance to formulations based on such neonicotinoids, which can also be expected for non-target insects. This research aimed to study the effects of a formulation based on TMX [Cruiser® 350 FS (CRZ)] on the life traits of Chironomus xanthus filial generation (F1) and compare it with the parental generation (P). Environmentally relevant concentrations of CRZ significantly decreased larvae growth P generation , also slowing and decreasing their emergence. Larvae of the F1 generation were less sensitive than their parents, suggesting that the progeny were able to thrive and perform basic physiological functions better than the parental generation. Our results highlight that insect resistance to neonicotinoids may be associated with the better performance of the filial generation, which is related to the change in affinities of the active ingredient for the sub-units constituting the nAChRs subtypes of F1 organisms, inherited from P organisms that were able to survive and reproduce. Moreover, further studies using biochemical and omics tools should be performed to disentangle the specific changes occurring at the nAChRs throughout insect development.

Recent progress in the structural study of ion channels as insecticide targets

Ion channels, many expressed in insect neural and muscular systems, have drawn huge attention as primary targets of insecticides. With the recent technical breakthroughs in structural biology, especially in cryo-electron microscopy (cryo-EM), many new high-resolution structures of ion channel targets, apo or in complex with insecticides, have been solved, shedding light on the molecular mechanism of action of the insecticides and resistance mutations. These structures also provide accurate templates for structure-based insecticide screening and rational design. This review summarizes the recent progress in the structural studies of 5 ion channel families: the ryanodine receptor (RyR), the nicotinic acetylcholine receptor (nAChR), the voltage-gated sodium channel (VGSC), the transient receptor potential (TRP) channel, and the ligand-gated chloride channel (LGCC). We address the selectivity of the channel-targeting insecticides by examining the conservation of key coordinating residues revealed by the structures. The possible resistance mechanisms are proposed based on the locations of the identified resistance mutations on the 3D structures of the target channels and their impacts on the binding of insecticides. Finally, we discuss how to develop "green" insecticides with a novel mode of action based on these high-resolution structures to overcome the resistance.

Comparative Transcriptome Analysis to Reveal Differentially Expressed Cytochrome P450 in Response to Imidacloprid in the Aphid Lion, Chrysoperla zastrowi sillemi (Esben-Petersen)

The aphid lion, Chrysoperla zastrowi sillemi (Neuroptera: Chrysopidae) is a highly effective beneficial predator of many agricultural pests and has developed resistance to several insecticides. Understanding the molecular mechanism of insecticide resistance in the predators is crucial for its effective application in IPM programs. Therefore, transcriptomes of imidacloprid-resistant and susceptible strains have been assessed using RNA-seq. Cytochrome P450 is one of the important gene families involved in xenobiotic metabolism. Hence, our study focused on the CYP gene family where mining, nomenclature, and phylogenetic analysis revealed a total of 95 unique CYP genes with considerable expansion in CYP3 and CYP4 clans. Further, differential gene expression (DGE) analysis revealed ten CYP genes from CYP3 and CYP4 clans to be differentially expressed, out of which nine genes (CYP4419A1, CYP4XK1, CYP4416A10, CYP4416A-fragment8, CYP6YL1, CYP6YH6, CYP9GK-fragment16, CYP9GN2, CYP9GK6) were downregulated and one (CYP9GK3) was upregulated in the resistant strain as compared to the susceptible strain. Expression validation by quantitative real-time PCR (qRT-PCR) is consistent with the DGE results. The expansion and differential expression of CYP genes may be an indicator of the capacity of the predator to detoxify a particular group of insecticides.

Resistance to dicyclanil and imidacloprid in the sheep blowfly, Lucilia cuprina, in Australia

BACKGROUND

The sheep blowfly, Lucila cuprina, is a myiasis-causing parasite responsible for significant production losses and welfare issues for the Australian sheep industry. Control relies largely on the use of insecticides. The pyrimidine compound, dicyclanil, is the predominant control chemical, although other insecticides also are used, including imidacloprid, ivermectin, cyromazine and spinosad. We investigated in vitro resistance patterns and mechanisms in field-collected blowfly strains.

RESULTS

The Walgett 2019 strain showed significant levels of resistance to both dicyclanil and imidacloprid, with resistance factors at the IC₅₀ of 26- and 17-fold, respectively, in in vitro bioassays. Co-treatment with the cytochrome P450 inhibitor, aminobenzotriazole, resulted in significant levels of synergism for dicyclanil and imidacloprid (synergism ratios of 7.2- and 6.1-fold, respectively), implicating cytochrome P450 in resistance to both insecticides. Cyp12d1 transcription levels were increased up to 40-fold throughout the larval life stages in the resistant strain compared to a reference susceptible strain, whereas transcription levels of some other cyp genes (6g1, 4d1, 28d1) did not differ between the strains. Similar resistance levels also were observed in flies collected from the same property in two subsequent years.

CONCLUSION

This study indicates that in vitro resistance to both dicyclanil and imidacloprid in this field-collected blowfly strain is likely mediated by cytochrome P450, with Cyp12d1 implicated as the enzyme responsible; however, it remains possible that another P450 also may be involved. A common resistance mechanism for the two drugs has important implications for drug rotation strategies designed to prolong the useful life of flystrike control chemicals. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

MicroRNA-190-5p confers chlorantraniliprole resistance by regulating CYP6K2 in Spodoptera frugiperda (Smith)

The fall armyworm Spodoptera frugiperda (Smith) (FAA) is responsible for considerable losses in grain production, and chemical control is the most effective strategy. However, frequent insecticide application can lead to the development of resistance. In insects, cytochrome P450 plays a crucial role in insecticide metabolism. CYP6K2 is related to FAA resistance to chlorantraniliprole. However, the regulatory mechanism of CYP6K2 expression is poorly understood. In this study, a conserved target of isolated miRNA-190-5p was located in the 3' UTR of CYP6K2 in FAA. A luciferase reporter analysis showed that in FAA, miRNA-190-5p can combine with the 3'UTR of CYP6K2 to suppress its expression. Injected miRNA-190-5p agomir significantly reduced CYP6K2 abundance by 54.6% and reduced tolerance to chlorantraniliprole in FAA larvae, whereas injected miRNA-190-5p antagomir significantly increased CYP6K2 abundance by 1.77-fold and thus improved chlorantraniliprole tolerance in FAA larvae. These results provide a basis for further research on the posttranscriptional regulatory mechanism of CYP6K2 and will facilitate further study on the function of miRNAs in regulating tolerance to chlorantraniliprole in FAA.

An innovative approach of bioremediation in enzymatic degradation of xenobiotics

Worldwide, environmental pollution due to a complex mixture of xenobiotics has become a serious concern. Several xenobiotic compounds cause environmental contamination due to their severe toxicity, prolonged exposure, and limited biodegradability. From the past few decades, microbial-assisted degradation (bioremediation) of xenobiotic pollutants has evolved as the most effective, eco-friendly, and valuable approach. Microorganisms have unique metabolism, the capability of genetic modification, diversity of enzymes, and various degradation pathways necessary for the bioremediation process. Microbial xenobiotic degradation is effective but a slow process that limits its application in bioremediation. However, the study of microbial enzymes for bioremediation is gaining global importance. Microbial enzymes have a huge ability to transform contaminants into non-toxic forms and thereby reduce environmental pollution. Recently, various advanced techniques, including metagenomics, proteomics, transcriptomics, metabolomics are effectively utilized for the characterization, metabolic machinery, new proteins, metabolic genes of microorganisms involved in the degradation process. These advanced molecular techniques provide a thorough understanding of the structural and functional aspects of complex microorganisms. This review gives a brief note on xenobiotics and their impact on the environment. Particular attention will be devoted to the class of pollutants and the enzymes such as cytochrome P450, dehydrogenase, laccase, hydrolase, protease, lipase, etc. capable of converting these pollutants into innocuous products. This review attempts to deliver knowledge on the role of various enzymes in the biodegradation of xenobiotic pollutants, along with the use of advanced technologies like recombinant DNA technology and Omics approaches to make the process more robust and effective.

Genomic organization and expression pattern of cytochrome P450 genes in the wolf spider Pardosa pseudoannulata

As one of the dominant natural enemies for insect pests, the pond wolf spider, Pardosa pseudoannulata, plays important roles in pest control. Insecticide applications threaten P. pseudoannulata and consequently weaken its control effects. The roles of P450 monooxygenases in insecticide detoxifications have been richly reported in insects, but there are few reported in spiders. In this study, 120 transcripts encoding P. pseudoannulata P450s were identified based on whole genome sequencing. Compared to P450s of Aedes aegypti and Nilaparvata lugens, several novel P450 families were found, such as CYP3310. KEGG analysis of the CYP3310 family indicated that the family might be involved in the synthesis and metabolism of polyunsaturated fatty acids and hydrocarbons. The potential P450s involved in insecticide metabolism were obtained according to the high FPKM values in fat bodies based on transcriptome sequencing. However, none of the selected P450 genes was significantly upregulated by the treatments of deltamethrin or imidacloprid. The present study provides genomic and transcriptomic information of spider P450s, especially for their roles in the synthesis and metabolism of endogenous and exogenous compounds, such as polyunsaturated fatty acids, hydrocarbons and insecticides.

Experimental evolution supports the potential of neonicotinoid-pyrethroid combination for managing insecticide resistance in malaria vectors

The introduction of neonicotinoids for managing insecticide resistance in mosquitoes is of high interest as they interact with a biochemical target not previously used in public health. In this concern, Bayer developed a combination of the neonicotinoid clothianidin and the pyrethroid deltamethrin (brand name Fludora Fusion) as a new vector control tool. Although this combination proved to be efficient against pyrethroid-resistant mosquitoes, its ability to prevent the selection of pyrethroid and neonicotinoid resistance alleles was not investigated. In this context, the objective of this work was to study the dynamics and the molecular mechanisms of resistance of An. gambiae to the separated or combined components of this combination. A field-derived An. gambiae line carrying resistance alleles to multiple insecticides at low frequencies was used as a starting for 33 successive generations of controlled selection. Resistance levels to each insecticide and target site mutation frequencies were monitored throughout the selection process. Cross resistance to other public health insecticides were also investigated. RNA-seq was used to compare gene transcription variations and polymorphisms across all lines. This study confirmed the potential of this insecticide combination to impair the selection of resistance as compared to its two separated components. Deltamethrin selection led to the rapid enrichment of the kdr L1014F target-site mutation. Clothianidin selection led to the over-transcription of multiple cytochrome P450s including some showing high homology with those conferring neonicotinoid resistance in other insects. A strong selection signature associated with clothianidin selection was also observed on a P450 gene cluster previously associated with resistance. Within this cluster, the gene CYP6M1 showed the highest selection signature together with a transcription profile supporting a role in clothianidin resistance. Modelling the impact of point mutations selected by clothianidin on CYP6M1 protein structure showed that selection retained a protein variant with a modified active site potentially enhancing clothianidin metabolism. In the context of the recent deployment of neonicotinoids for mosquito control and their frequent usage in agriculture, the present study highlights the benefit of combining them with other insecticides for preventing the selection of resistance and sustaining vector control activities.

Transcriptional regulation of xenobiotic detoxification genes in insects - An overview

Arthropods have well adapted to the vast array of chemicals they encounter in their environment. Whether these xenobiotics are plant allelochemicals or anthropogenic insecticides one of the strategies they have developed to defend themselves is the induction of detoxification enzymes. Although upregulation of detoxification enzymes and efflux transporters in response to specific inducers has been well described, in insects, yet, little is known on the transcriptional regulation of these genes. Over the past twenty years, an increasing number of studies with insects have used advanced genetic tools such as RNAi, CRISPR/Cas9 and reporter gene assays to dissect the genomic grounds of their xenobiotic response and hence contributed substantially in improving our knowledge on the players involved. Xenobiotics are partly recognized by various "xenobiotic sensors" such as membrane-bound or nuclear receptors. This initiates a molecular reaction cascade ultimately leading to the translocation of a transcription factor to the nucleus that recognizes and binds to short sequences located upstream their target genes to activate transcription. To date, a number of signaling pathways were shown to mediate the upregulation of detoxification enzymes in arthropods and to play a role in either metabolic resistance to insecticides or host-plant adaptation. These include nuclear receptors AhR/ARNT and HR96, GPCRs, CncC and MAPK/CREB. Recent work reveals that upregulation and activation of some components of these pathways as well as polymorphism in the binding motifs of transcription factors are linked to insects' adaptive processes. The aim of this mini-review is to summarize and describe recent work that shed some light on the main regulatory routes of detoxification gene expression in insects.

Reductive Cytochrome P450 Reactions and Their Potential Role in Bioremediation

Cytochrome P450 enzymes, or P450s, are haem monooxygenases renowned for their ability to insert one atom from molecular oxygen into an exceptionally broad range of substrates while reducing the other atom to water. However, some substrates including many organohalide and nitro compounds present little or no opportunity for oxidation. Under hypoxic conditions P450s can perform reductive reactions, contributing electrons to drive reductive elimination reactions. P450s can catalyse dehalogenation and denitration of a range of environmentally persistent pollutants including halogenated hydrocarbons and nitroamine explosives. P450-mediated reductive dehalogenations were first discovered in the context of human pharmacology but have since been observed in a variety of organisms. Additionally, P450-mediated reductive denitration of synthetic explosives has been discovered in bacteria that inhabit contaminated soils. This review will examine the distribution of P450-mediated reductive dehalogenations and denitrations in nature and discuss synthetic biology approaches to developing P450-based reagents for bioremediation.

An update of the Worldwide Integrated Assessment (WIA) on systemic insecticides. Part 3: alternatives to systemic insecticides

Over-reliance on pesticides for pest control is inflicting serious damage to the environmental services that underpin agricultural productivity. The widespread use of systemic insecticides, neonicotinoids, and the phenylpyrazole fipronil in particular is assessed here in terms of their actual use in pest management, effects on crop yields, and the development of pest resistance to these compounds in many crops after two decades of usage. Resistance can only be overcome in the longterm by implementing methods that are not exclusively based on synthetic pesticides. A diverse range of pest management tactics is already available, all of which can achieve efficient pest control below the economic injury level while maintaining the productivity of the crops. A novel insurance method against crop failure is shown here as an example of alternative methods that can protect farmer's crops and their livelihoods without having to use insecticides. Finally, some concluding remarks about the need for a new framework for a truly sustainable agriculture that relies mainly on natural ecosystem services instead of chemicals are included; this reinforcing the previous WIA conclusions (van der Sluijs et al. Environ Sci Pollut Res 22:148-154, 2015).

Transcriptome profiling and functional analysis suggest that the constitutive overexpression of four cytochrome P450s confers resistance to abamectin in Tetranychus urticae from China

BACKGROUND

The two-spotted spider mite Tetranychus urticae is a polyphagous and cosmopolitan pest that has developed high resistance to abamectin, making it difficult to control. Although 'target resistance' related to glutamate-gated chloride channel mutations was found in T. urticae field populations in China, other resistance mechanisms appear to be involved. Here, we conducted genome-wide transcriptome profiling using RNA-sequencing of two abamectin-resistant populations (NB-ZJ and SY-BJ) and one susceptible strain (Lab-SS) to identify differentially expressed genes that might contribute to the resistance of T. urticae to abamectin in China.

RESULTS

Our experiments showed that abamectin resistance was synergized by piperonyl butoxide (PBO) and triphenyl phosphate (TPP), with synergistic ratios (SR) of 2.95-fold and 2.21-fold for PBO and 3.55-fold and 2.84-fold for TPP in NB-ZJ and SY-BJ populations, respectively. Transcriptome data and quantitative real-time PCR (qRT-PCR) revealed that seven detoxification enzyme genes were overexpressed in the two resistant populations. Furthermore, functional analysis by RNA interference (RNAi) indicated that the mortality caused by abamectin was significantly increased by the separate silencing of the P450 genes CYP389C10, CYP392D8, CYP392A11, and CYP392A12.

CONCLUSION

qRT-PCR expression and RNAi data suggest that the overexpression of P450 genes CYP389C10, CYP392D8, CYP392A11, and CYP392A12 may be involved in the abamectin-resistance of field populations of T. urticae in China. This knowledge could facilitate the elucidation of resistance mechanisms and the development of resistance management of T. urticae field populations. © 2020 Society of Chemical Industry.

Evidence for cometabolic transformation of weathered toxaphene under aerobic conditions using camphor as a co-substrate

AIMS

Toxaphene is a persistent organic pollutant, composed of approximately 1000 highly chlorinated bicyclic terpenes. The purpose of this study was to evaluate if camphor, a structural analogue of toxaphene, could stimulate aerobic biotransformation of weathered toxaphene.

METHODS AND RESULTS

Two enrichment cultures that degrade camphor as the sole carbon source were established from contaminated soil and biosolids. These cultures were used to evaluate aerobic transformation of weathered toxaphene. Only the biosolids culture could transform compounds of technical toxaphene (CTTs) in the presence of camphor, while no transformation was observed in the presence of glucose or with toxaphene as a sole carbon source. The transformed toxaphene had lower concentration of CTTs with longer retention times, and higher concentration of compounds with lower retention times. Gas chromatography with electron capture negative ion mass spectrometry (GC/ECNI-MS) showed that aerobic biotransformation mainly occurred with Cl₈ - and Cl₉ -CTTs compounds. The patterns of Cl₆ - and Cl₇ -CTTs were also simplified albeit to a much lesser extent. Seven camphor-degrading bacteria were isolated from the enrichment culture but none of them could degrade toxaphene.

CONCLUSION

Camphor degrading culture can aerobically transform CCTs via reductive pathway probably by co-metabolism using camphor as a co-substrate.

SIGNIFICANCE AND IMPACT OF THE STUDY

Since camphor is naturally produced by different plants, this study suggests that stimulation of aerobic transformation of toxaphene may occur in nature. Moreover plants, which produce camphor or similar compounds, might be used in bioremediation of contaminated soils.

Neonicotinoid Insecticides: Molecular Targets, Resistance, and Toxicity

Neonicotinoids have been used to protect crops and animals from insect pests since the 1990s, but there are concerns regarding their adverse effects on nontarget organisms, notably on bees. Enhanced resistance to neonicotinoids in pests is becoming well documented. We address the current understanding of neonicotinoid target site interactions, selectivity, and metabolism not only in pests but also in beneficial insects such as bees. The findings are relevant to the management of both neonicotinoids and the new generation of pesticides targeting insect nicotinic acetylcholine receptors.

Post-transcriptional modulation of cytochrome P450s, Cyp6g1 and Cyp6g2, by miR-310s cluster is associated with DDT-resistant Drosophila melanogaster strain 91-R

The role of miRNAs in mediating insecticide resistance remains largely unknown, even for the model species Drosophila melanogaster. Building on prior research, this study used microinjection of synthetic miR-310s mimics into DDT-resistant 91-R flies and observed both a significant transcriptional repression of computationally-predicted endogenous target P450 detoxification genes, Cyp6g1 and Cyp6g2, and also a concomitant increase in DDT susceptibility. Additionally, co-transfection of D. melanogaster S2 cells with dual luciferase reporter constructs validated predictions that miR-310s bind to target binding sites in the 3ʹ untranslated regions (3ʹ-UTR) of both Cyp6g1 and Cyp6g2 in vitro. Findings in the current study provide empirical evidence for a link between reduced miRNA expression and an insecticidal resistance phenotype through reduced targeted post-transcriptional suppression of transcripts encoding proteins involved in xenobiotic detoxification. These insights are important for understanding the breadth of adaptive molecular changes that have contributed to the evolution of DDT resistance in D. melanogaster.

Genomic and transcriptomic analyses in Drosophila suggest that the ecdysteroid kinase-like (EcKL) gene family encodes the 'detoxification-by-phosphorylation' enzymes of insects

Phosphorylation is a phase II detoxification reaction that, among animals, occurs near exclusively in insects, but the enzymes responsible have never been cloned or otherwise identified. We propose the hypothesis that members of the arthropod-specific ecdysteroid kinase-like (EcKL) gene family encode detoxicative kinases. To test this hypothesis, we annotated the EcKL gene family in 12 species of Drosophila and explored their evolution within the genus. Many ancestral EcKL clades are evolutionarily unstable and have experienced repeated gene gain and loss events, while others are conserved as single-copy orthologs. Leveraging multiple published gene expression datasets from D. melanogaster, and using the cytochrome P450s-a classical detoxification family-as a test case, we demonstrate relationships between xenobiotic induction, detoxification tissue-enriched expression and evolutionary instability in the EcKLs and the P450s. We devised a systematic method for identifying candidate detoxification genes in large gene families that is concordant with experimentally determined functions of P450 genes in D. melanogaster. Applying this method to the EcKLs suggested a significant proportion of these genes play roles in detoxification, and that the EcKLs may constitute a detoxification gene family in insects. Additionally, we estimate that between 11 and 16 uncharacterised D. melanogaster P450s are strong detoxification candidates. Lastly, we also found previously unreported genomic and transcriptomic variation in a number of EcKLs and P450s associated with toxic stress phenotypes using a targeted phenome-wide association study (PheWAS) approach in D. melanogaster, presenting multiple future avenues of research for detoxification genetics in this species.

Transcription profiling and characterization of Dermanyssus gallinae cytochrome P450 genes involved in beta-cypermethrin resistance

The poultry red mite, Dermanyssus gallinae, poses a significant threat to hen health and poultry husbandry. D. gallinae has typically been controlled using synthetic acaricides, like pyrethroids, but increased resistance to pyrethroids has been found in poultry red mite populations worldwide. Pyrethroids resistance in arthropods has been associated to cytochrome P450 monooxygenases (P450s), a main member of a group of detoxification enzymes. To explore the potential contribution of P450s to the resistance to pyrethroids in D. gallinae, we first identified and then characterized four P450s genes. Phylogenetic analysis revealed that the four P450s genes in D. gallinae belong to three different clades, with two in the CYP-6, one in the CYP-4 and one in the CYP-2. All four P450s genes were expressed in a similar pattern in D. gallinae at different stages of development, and showed high expression in the adult stage, indicating that they played a role in mite development. Simultaneously, constitutive over-expression of Deg-CYP-3, a clade associated with pesticide metabolism, was detected in a resistant strain (RS) compared with a susceptible strain (SS). When exposed to beta-cypermethrin, the four P450s gene transcripts in the RS strain increased in a time-dependent manner. In particular, Deg-CYP-3 expression increased 5-fold compared to gene expression in control group at 12 h, although the four P450s genes were not induced in the SS strain. Our results show the first insights into the molecular characteristics of P450s genes in D. gallinae. The elevated presence of P450s genes in the RS strain, indicated by their constitutive over-expression and their inducible expression, suggests that they confer resistance to beta-cypermethrin, and are involved in its detoxification.

The reference genome of the selfing fish Kryptolebias hermaphroditus: Identification of phases I and II detoxification genes

The selfing fish Kryptolebias hermaphroditus has unique reproductive system for self-fertilization, making genetically homozygous offsprings. Here, we report on high density genetic map-based genome assembly for the K. hermaphroditus Panama line (PanRS). The numbers of scaffolds were 5212 and the genome was 683,992,224 bp (N50 = 27.45 Mb). The length of anchored scaffold onto 24 linkage groups was 652,231,070 bp (95.3% of genome) with 0.01% of the gap and 39.33% of GC content and complete Benchmarking Universal Single-Copy Orthologs value was 96.6%. The numbers of annotated genes were 36,756 (average gene length 1368 bp) with the GC content of 54.1%. To examine the difference between the two sister species in the genus Kryptolebias, we compared the genomes of K. hermaphroditus PanRS and Kryptolebias marmoratus PAN line on the composition of transposable elements. To demonstrate applications of genome library, phase I and II detoxification related gene families have been analyzed, and compared the syntenies containing loci of CYP and GST genes on linkage groups. This K. hermaphroditus genome information will be helpful for a better understanding on genome-wide mechanistic view of detoxification and antioxidant-related genes over evolution in the view of fish environmental ecotoxicology.

The Inducible CYP4C71 Can Metabolize Imidacloprid in Laodelphax striatellus (Hemiptera: Delphacidae)

Laodelphax striatellus (Fallén) is an important rice pest species which has developed high resistance to imidacloprid. Previous studies have demonstrated that CYP6AY3v2 and CYP353D1v2 were constitutively overexpressed in a imidacloprid resistant strain and can metabolize imidacloprid to mediated metabolic resistance. Further studies still needed to explore whether there are other L. striatellus P450 enzymes that can also metabolize imidacloprid. In this study, the expression level of L. striatellus CYP4C71 was significantly upregulated both in laboratory strains and field strains of L. striatellus after imidacloprid treatment for 4 h. The capability of CYP4C71 to metabolize imidacloprid was investigated. The full-length CYP4C71 was cloned, and its open reading frame was 1,515 bp with an enzyme estimated to be 505 amino acid residues in size. Furthermore, CYP4C71 was heterologously expressed along with L. striatellus cytochrome P450 reductase (CPR) in insect cells. A carbon monoxide difference spectra analysis confirmed the successful expression of CYP4C71. The recombinant CYP4C71 showed high P450 O-demethylation activity with PNP as a substrate. In vitro metabolism studies showed that recombinant CYP4C71 can metabolize imidacloprid to an easily excreted hydroxy-form. The rate of imidacloprid depletion in response to imidacloprid concentration revealed Michaelis Menten kinetics (R2 fitted curve = 0.99) with a relative low affinity: Kcat = 0.032 ± 0.009 pmol depleted imidacloprid/min/pmol P450 and Km=85.19 ± 2.93 μM. A relative big Km (85.19 ± 2.93 μM) indicated relative low imidacloprid's affinity for the CYP4C71 enzyme. In conclusion, CYP4C71 was another P450 enzyme that can metabolize imidacloprid with a relatively low affinity.

The cytochrome P450 CYP389C16 contributes to the cross-resistance between cyflumetofen and pyridaben in Tetranychus cinnabarinus (Boisduval)

BACKGROUND

Acaricide resistance is a serious problem in spider mites. Cyflumetofen is a new complex II inhibitor, whereas pyridaben acts at complex I and has been used for decades. Although cross-resistance between cyflumetofen and pyridaben has been observed in Tetranychus cinnabarinus, the specific mechanisms at play have not yet been investigated.

RESULTS

Investigation into the cross-resistance mechanisms identified five P450s, among which CYP389C16 was evaluated as the most likely candidate conferring cross-resistance. Knockdown of CYP389C16 expression via RNA interference diminished the level of cross-resistance in the cyflumetofen-resistant strain. In addition, recombinant CYP389C16 (40 pmol) effectively metabolized 25.0 ± 0.7% of cyflumetofen, 39.7 ± 1.0% of pyridaben, and 69.3 ± 3.3% of AB-1 (active de-esterified metabolite of cyflumetofen) within 2 h. In addition, hydroxylation metabolite of AB-1 was identified by HPLC-MS/MS.

CONCLUSIONS

The study reveals that overexpressed CYP389C16 is involved in the cross-resistance between cyflumetofen and pyridaben in T. cinnabarinus. © 2019 Society of Chemical Industry.

Identification and functional characterisation of a novel N-cyanoamidine neonicotinoid metabolising cytochrome P450, CYP9Q6, from the buff-tailed bumblebee Bombus terrestris

Recent work has shown that two bumblebee (Bombus terrestris) cytochrome P450s of the CYP9Q subfamily, CYP9Q4 and CYP9Q5, are important biochemical determinants of sensitivity to neonicotinoid insecticides. Here, we report the characterisation of a third P450 gene CYP9Q6, previously mis-annotated in the genome of B. terrestris, encoding an enzyme that metabolises the N-cyanoamidine neonicotinoids thiacloprid and acetamiprid with high efficiency. The genomic location and complete ORF of CYP9Q6 was corroborated by PCR and its metabolic activity characterised in vitro by expression in an insect cell line. CYP9Q6 metabolises both thiacloprid and acetamiprid more rapidly than the previously reported CYP9Q4 and CYP9Q5. We further demonstrate a direct, in vivo correlation between the expression of the CYP9Q6 enzyme in transgenic Drosophila melanogaster and an increased tolerance to thiacloprid and acetamiprid. We conclude that CYP9Q6 is an efficient metaboliser of N-cyanoamidine neonicotinoids and likely plays a key role in the high tolerance of B. terrestris to these insecticides.

Characterization of sulfoxaflor resistance in the brown planthopper, Nilaparvata lugens (Stål)

BACKGROUND

Sulfoxaflor is a new insecticide for controlling Nilaparvata lugens in the field. This study was conducted to investigate the risk of resistance development, the cross-resistance spectrum and the mechanisms of sulfoxaflor resistance in N. lugens.

RESULTS

A sulfoxaflor-resistant strain was obtained from a field population by successive selection with sulfoxaflor for 39 generations in the laboratory. Sulfoxaflor-resistant populations showed significant levels of cross-resistance to dinotefuran, nitenpyram, thiamethoxam, clothianidin, imidacloprid and cycloxaprid. However, they exhibited only minor or no cross-resistance to isoprocarb, etofenprox, chlorpyrifos, triflumezopyrim and buprofezin. Sulfoxaflor was synergized by the inhibitor piperonyl butoxide (PBO) in the sulfoxaflor-resistant strain (SFX-SEL) with 2.69-fold relative synergistic ratios compared with the unselected strain (UNSEL). Compared with UNSEL, the P450 enzyme activity of SFX-SEL was increased 3.50 times, and eight P450 genes were upregulated more than 2.0-fold in SFX-SEL. RNAi reduced the expression of CYP6ER1 (36.87-fold change) and significantly enhanced the susceptibility of SFX-SEL to sulfoxaflor.

CONCLUSION

Resistance development and cross-resistance risk of sulfoxaflor-resistance in N. lugens is evident. The enhanced detoxification of P450 enzymes caused by upregulation of several P450 genes is considered to be the metabolic resistance mechanism. These results suggest that CYP6ER1 might play an important role in sulfoxaflor resistance in N. lugens. © 2018 Society of Chemical Industry.

Global transcriptome profiling and functional analysis reveal that tissue-specific constitutive overexpression of cytochrome P450s confers tolerance to imidacloprid in palm weevils in date palm fields

Background

Cytochrome P450-dependent monooxygenases (P450s), constituting one of the largest and oldest gene superfamilies found in many organisms from bacteria to humans, play a vital role in the detoxification and inactivation of endogenous toxic compounds. The use of various insecticides has increased over the last two decades, and insects have developed resistance to most of these compounds through the detoxifying function of P450s. In this study, we focused on the red palm weevil (RPW), Rhynchophorus ferrugineus, the most devastating pest of palm trees worldwide, and demonstrated through functional analysis that upregulation of P450 gene expression has evolved as an adaptation to insecticide stress arising from exposure to the neonicotinoid-class systematic insecticide imidacloprid.

Results

Based on the RPW global transcriptome analysis, we identified 101 putative P450 genes, including 77 likely encoding protein coding genes with ubiquitous expression. A phylogenetic analysis revealed extensive functional and species-specific diversification of RPW P450s, indicating that multiple CYPs actively participated in the detoxification process. We identified highly conserved paralogs of insect P450s that likely play a role in the development of resistance to imidacloprid: Drosophila Cyp6g1 (CYP6345J1) and Bemisia tabaci CYP4C64 (CYP4LE1). We performed a toxicity bioassay and evaluated the induction of P450s, followed by the identification of overexpressed P450s, including CYP9Z82, CYP6fra5, CYP6NR1, CYP6345J1 and CYP4BD4, which confer cross-resistance to imidacloprid. In addition, under imidacloprid insecticide stress in a date palm field, we observed increased expression of various P450 genes, with CYP9Z82, CYP4BD4, CYP6NR1 and CYP6345J1 being the most upregulated detoxification genes in RPWs. Expression profiling and cluster analysis revealed P450 genes with multiple patterns of induction and differential expression. Furthermore, we used RNA interference to knock down the overexpressed P450s, after which a toxicity bioassay and quantitative expression analysis revealed likely candidates involved in metabolic resistance against imidacloprid in RPW. Ingestion of double-stranded RNA (dsRNA) successfully knocked down the expression of CYP9Z82, CYP6NR1 and CYP345J1 and demonstrated that silencing of CYP345J1 and CYP6NR1 significantly decreased the survival rate of adult RPWs treated with imidacloprid, indicating that overexpression of these two P450s may play an important role in developing tolerance to imidacloprid in a date palm field.

Conclusion

Our study provides useful background information on imidacloprid-specific induction and overexpression of P450s, which may enable the development of diagnostic tools/markers for monitoring the spread of insecticide resistant RPWs. The observed trend of increasing tolerance to imidacloprid in the date palm field therefore indicated that strategies for resistance management are urgently needed.

Electronic supplementary material

The online version of this article (10.1186/s12864-019-5837-4) contains supplementary material, which is available to authorized users.

Structural Variants and Selective Sweep Foci Contribute to Insecticide Resistance in the Drosophila Genetic Reference Panel

Patterns of nucleotide polymorphism within populations of Drosophila melanogaster suggest that insecticides have been the selective agents driving the strongest recent bouts of positive selection. However, there is a need to explicitly link selective sweeps to the particular insecticide phenotypes that could plausibly account for the drastic selective responses that are observed in these non-target insects. Here, we screen the Drosophila Genetic Reference Panel with two common insecticides; malathion (an organophosphate) and permethrin (a pyrethroid). Genome-wide association studies map survival on malathion to two of the largest sweeps in the D. melanogaster genome; Ace and Cyp6g1. Malathion survivorship also correlates with lines which have high levels of Cyp12d1, Jheh1 and Jheh2 transcript abundance. Permethrin phenotypes map to the largest cluster of P450 genes in the Drosophila genome, however in contrast to a selective sweep driven by insecticide use, the derived allele seems to be associated with susceptibility. These results underscore previous findings that highlight the importance of structural variation to insecticide phenotypes: Cyp6g1 exhibits copy number variation and transposable element insertions, Cyp12d1 is tandemly duplicated, the Jheh loci are associated with a Bari1 transposable element insertion, and a Cyp6a17 deletion is associated with susceptibility.

Identification and interaction of multiple genes resulting in DDT resistance in the 91-R strain of Drosophila melanogaster by RNAi approaches

4,4'-dichlorodiphenyltrichloroethane (DDT) has been re-recommended by the World Health Organization for malaria mosquito control. Previous DDT use has resulted in resistance, and with continued use resistance will likely increase in terms of level and extent. Drosophila melanogaster is a model dipteran with a well annotated genome allowing both forward and reverse genetic manipulation, numerous studies done on insecticide resistance mechanisms, and is related to malaria mosquitoes allowing for extrapolation. The 91-R strain of D. melanogaster is highly resistant to DDT (>1500-fold) and recently, reduced penetration, increased detoxification, and direct excretion have been identified as resistance mechanisms. Their interactions, however, remain unclear. Use of Gal4/UAS-RNAi transgenic lines of D. melanogaster allowed for the targeted knockdown of genes putatively involved in DDT resistance and has identified the role of several cuticular proteins (Cyp4g1 and Lcp1), cytochrome P450 monooxygenases (Cyp6g1 and Cyp12d1), and ATP binding cassette transporters (Mdr50, Mdr65, and Mrp1) involved in decreased sensitivity to DDT. These above findings have been further validated in 91-R flies using a nanoparticle-enhanced RNAi strategy, directly implication these genes in DDT resistance in 91-R flies.

Evidence for activation of nitenpyram by a mitochondrial cytochrome P450 in Drosophila melanogaster

BACKGROUND

Nitenpyram is a member of the economically important neonicotinoid class of insecticides. The in vivo metabolism of nitenpyram is not well characterised, but cytochrome P450 activity is the major mechanism of resistance to neonicotinoids identified in insect pests, and P450s metabolise other neonicotinoids including imidacloprid.

RESULTS

Here, we used the GAL4-UAS targeted expression system to direct RNA interference (RNAi) against the cytochrome P450 redox partners to interrupt P450 functions in specific tissues in Drosophila melanogaster. RNAi of the mitochondrial redox partner defective in the avoidance of repellents (dare) in the digestive tissues reduced nitenpyram mortality, suggesting an activation step in the metabolism of nitenpyram carried out by a mitochondrial P450. RNAi of the mitochondrial cytochrome P450 Cyp12a5, which is expressed in the digestive tissues, resulted in the same phenotype, and transgenic overexpression of Cyp12a5 increased nitenpyram sensitivity.

CONCLUSION

These results suggest that in vivo metabolism of nitenpyram by the mitochondrial P450 CYP12A5 results in the formation of a product with higher toxicity than the parent compound. © 2018 Society of Chemical Industry.

Strategies for the construction of insect P450 fusion enzymes

Cytochrome P450 monooxygenases (P450s) are ubiquitous enzymes with a broad substrate spectrum. Insect P450s are known to catalyze reactions such as the detoxification of insecticides and the synthesis of hydrocarbons, which makes them useful for many industrial processes. Unfortunately, it is difficult to utilize P450s effectively because they must be paired with cytochrome P450 reductases (CPRs) to facilitate electron transfer from reduced nicotinamide adenine dinucleotide phosphate (NADPH). Furthermore, eukaryotic P450s and CPRs are membrane-anchored proteins, which means they are insoluble and therefore difficult to purify when expressed in their native state. Both challenges can be addressed by creating fusion proteins that combine the P450 and CPR functions while eliminating membrane anchors, allowing the production and purification of soluble multifunctional polypeptides suitable for industrial applications. Here we discuss several strategies for the construction of fusion enzymes combining insect P450 with CPRs.

Phylogenetic and functional characterization of ten P450 genes from the CYP6AE subfamily of Helicoverpa armigera involved in xenobiotic metabolism

The cotton bollworm, Helicoverpa armigera, is a generalist herbivore widely distributed over the world and is a major lepidopteran pest on cotton. Studies, especially from Asia, show that it relies on cytochrome P450 monooxygenases with broad substrate specificities to protect itself from pesticides. The number of P450s may have expanded in the processes of coping with the wide diversity of phytochemicals that the insect encounters among its numerous host plants. In order to examine the metabolic capabilities of these P450s, we focused here on all ten P450s of the Helicoverpa armigera CYP6AE subfamily, which can be easily induced by plant toxins and pyrethroids. These P450s, along with cytochrome P450 reductase, were heterologously expressed in insect cells and compared functionally. In vitro metabolism showed that all CYP6AE subfamily members can convert esfenvalerate to 4'-hydroxyesfenvalerate efficiently except CYP6AE20. In contrast, none of the recombinant CYP6AE enzymes could metabolise gossypol under our experimental conditions. Epoxidation capabilities were observed in the CYP6AE subfamily, aldrin can be converted to dieldrin at rates up to 0.45 ± 0.04 pmol/min/pmol P450. Seven P450s in this subfamily can metabolise imidacloprid, but with lower efficiency than Bemisia tabaci CYP6CM1vQ. CYP6AE20 had virtually no metabolic competence to these four compounds but could metabolise several model fluorogenic substrates. These results showed the broad substrate spectrum of H. armigera CYP6AE P450s and suggest a limited role of gossypol upon the evolution of H. armigera CYP6AE genes.

Prokaryotic functional expression and activity comparison of three CYP9A genes from the polyphagous pest Helicoverpa armigera

Cytochrome P450s (CYPs or P450s) have been long recognized as very important enzymes in the metabolism of xenobiotic and endogenous compounds, but only a few CYPs have been functionally characterized in insects. The effort in functional characterization of insect P450s is heavily hindered by technical difficulties in preparing active, individual P450 enzymes directly from the target insect. In this paper, we describe the functional expression of two additional pyrethroid resistance-associated CYP9A genes (CYP9A12 and CYP9A17) from the polyphagous pest Helicoverpa armigera in the facile Escherichia coli. The functionality of E. coli produced CYP9A12, CYP9A14, and CYP9A17 was investigated and activities of these CYP9As were compared against three probe substrates after reconstitution with NADPH-dependent cytochrome P450 reductase. The results showed that active forms of CYP9A12 and CYP9A17 were expressed in E. coli with a content of about 1.0-1.5 nmol mg-1 protein in membrane preparations. In vitro assays showed that CYP9A14 was capable of catalyzing O-dealkylation of methoxyresorufin (MROD), ethoxyresorufin (EROD), and benzyloxyresorufin (BROD), while CYP9A12 and CYP9A17 exhibited only MROD and EROD activities. Kinetic studies demonstrated that CYP9A14 had the greatest k cat/K m value for MROD, and CYP9A17 for EROD, while the lowest k cat/K m values for both MROD and EROD were observed for CYP9A12. The distinct biochemical traits suggest that the three paralogous CYP9As may play different roles in xenobiotic metabolism in this important pest.

ASGDB: a specialised genomic resource for interpreting Anopheles sinensis insecticide resistance

BACKGROUND

Anopheles sinensis is an important malaria vector in Southeast Asia. The widespread emergence of insecticide resistance in this mosquito species poses a serious threat to the efficacy of malaria control measures, particularly in China. Recently, the whole-genome sequencing and de novo assembly of An. sinensis (China strain) has been finished. A series of insecticide-resistant studies in An. sinensis have also been reported. There is a growing need to integrate these valuable data to provide a comprehensive database for further studies on insecticide-resistant management of An. sinensis.

RESULTS

A bioinformatics database named An. sinensis genome database (ASGDB) was built. In addition to being a searchable database of published An. sinensis genome sequences and annotation, ASGDB provides in-depth analytical platforms for further understanding of the genomic and genetic data, including visualization of genomic data, orthologous relationship analysis, GO analysis, pathway analysis, expression analysis and resistance-related gene analysis. Moreover, ASGDB provides a panoramic view of insecticide resistance studies in An. sinensis in China. In total, 551 insecticide-resistant phenotypic and genotypic reports on An. sinensis distributed in Chinese malaria-endemic areas since the mid-1980s have been collected, manually edited in the same format and integrated into OpenLayers map-based interface, which allows the international community to assess and exploit the high volume of scattered data much easier. The database has been given the URL: http://www.asgdb.org /.

CONCLUSIONS

ASGDB was built to help users mine data from the genome sequence of An. sinensis easily and effectively, especially with its advantages in insecticide resistance surveillance and control.

Buprofezin Is Metabolized by CYP353D1v2, a Cytochrome P450 Associated with Imidacloprid Resistance in Laodelphax striatellus

CYP353D1v2 is a cytochrome P450 related to imidacloprid resistance in Laodelphax striatellus. This work was conducted to examine the ability of CYP353D1v2 to metabolize other insecticides. Carbon monoxide difference spectra analysis indicates that CYP353D1v2 was successfully expressed in insect cell Sf9. The catalytic activity of CYP353D1v2 relating to degrading buprofezin, chlorpyrifos, and deltamethrin was tested by measuring substrate depletion and analyzing the formation of metabolites. The results showed the nicotinamide-adenine dinucleotide phosphate (NADPH)-dependent depletion of buprofezin (eluting at 8.7 min) and parallel formation of an unknown metabolite (eluting 9.5 min). However, CYP353D1v2 is unable to metabolize deltamethrin and chlorpyrifos. The recombinant CYP353D1v2 protein efficiently catalyzed the model substrate p-nitroanisole with a maximum velocity of 9.24 nmol/min/mg of protein and a Michaelis constant of Km = 6.21 µM. In addition, imidacloprid was metabolized in vitro by the recombinant CYP353D1v2 microsomes (catalytic constant Kcat) 0.064 pmol/min/pmol P450, Km = 6.41 µM. The mass spectrum of UPLC-MS analysis shows that the metabolite was a product of buprofezin, which was buprofezin sulfone. This result provided direct evidence that L. striatellus cytochrome P450 CYP353D1v2 is capable of metabolizing imidacloprid and buprofezin.

Imidacloprid is hydroxylated by Laodelphax striatellus CYP6AY3v2

Laodelphax striatellus (Fallén) is one of the most destructive pests of rice, and has developed high resistance to imidacloprid. Our previous work indicated a strong association between imidacloprid resistance and the overexpression of a cytochrome P450 gene CYP6AY3v2 in a L. striatellus imidacloprid resistant strain (Imid-R). In this study, a transgenic Drosophila melanogaster line that overexpressed the L. striatellus CYP6AY3v2 gene was established and was found to confer increased levels of imidacloprid resistance. Furthermore, CYP6AY3v2 was co-expressed with D. melanogaster cytochrome P450 reductase (CPR) in Spodoptera frugiperda 9 (SF9) cells. A carbon monoxide difference spectra analysis indicated that CYP6AY3v2 was expressed predominately in its cytochrome P450 (P450) form, which is indicative of a good-quality functional enzyme. The recombinant CYP6AY3v2 protein efficiently catalysed the model substrate P-nitroanisole to p-nitrophenol with a maximum velocity (V_max ) of 60.78 ± 3.93 optical density (mOD)/min/mg protein. In addition, imidacloprid itself was metabolized by the recombinant CYP6AY3v2/nicotinamide adenine dinucleotide 2'-phosphate reduced tetrasodium salt (NADPH) CPR microsomes in in vitro assays (catalytic constant (K_cat ) = 0.34 pmol/min/pmol P450, michaelis constant (K_m ) = 41.98 μM), and imidacloprid depletion and metabolite peak formation were with a time dependence. The data provided direct evidence that CYP6AY3v2 is capable of hydroxylation of imidacloprid and conferring metabolic resistance in L. striatellus.

Insights into DDT Resistance from the Drosophila melanogaster Genetic Reference Panel

Insecticide resistance is considered a classic model of microevolution, where a strong selective agent is applied to a large natural population, resulting in a change in frequency of alleles that confer resistance. While many insecticide resistance variants have been characterized at the gene level, they are typically single genes of large effect identified in highly resistant pest species. In contrast, multiple variants have been implicated in DDT resistance in Drosophila melanogaster; however, only the Cyp6g1 locus has previously been shown to be relevant to field populations. Here we use genome-wide association studies (GWAS) to identify DDT-associated polygenes and use selective sweep analyses to assess their adaptive significance. We identify and verify two candidate DDT resistance loci. A largely uncharacterized gene, CG10737, has a function in muscles that ameliorates the effects of DDT, while a putative detoxifying P450, Cyp6w1, shows compelling evidence of positive selection.

Multiple P450s and Variation in Neuronal Genes Underpins the Response to the Insecticide Imidacloprid in a Population of Drosophila melanogaster

Insecticide resistance is an economically important example of evolution in response to intense selection pressure. Here, the genetics of resistance to the neonicotinoid insecticide imidacloprid is explored using the Drosophila Genetic Reference Panel, a collection of inbred Drosophila melanogaster genotypes derived from a single population in North Carolina. Imidacloprid resistance varied substantially among genotypes, and more resistant genotypes tended to show increased capacity to metabolize and excrete imidacloprid. Variation in resistance level was then associated with genomic and transcriptomic variation, implicating several candidate genes involved in central nervous system function and the cytochrome P450s Cyp6g1 and Cyp6g2. CRISPR-Cas9 mediated removal of Cyp6g1 suggested that it contributed to imidacloprid resistance only in backgrounds where it was already highly expressed. Cyp6g2, previously implicated in juvenile hormone synthesis via expression in the ring gland, was shown to be expressed in metabolically relevant tissues of resistant genotypes. Cyp6g2 overexpression was shown to both metabolize imidacloprid and confer resistance. These data collectively suggest that imidacloprid resistance is influenced by a variety of previously known and unknown genetic factors.

Partitioning the roles of CYP6G1 and gut microbes in the metabolism of the insecticide imidacloprid in Drosophila melanogaster

Resistance to insecticides through enhanced metabolism is a worldwide problem. The Cyp6g1 gene of the vinegar fly, Drosophila melanogaster, is a paradigm for the study of metabolic resistance. Constitutive overexpression of this gene confers resistance to several classes of insecticides, including the neonicotinoid imidacloprid (IMI). The metabolism of IMI in this species has been previously shown to yield oxidative and nitro-reduced metabolites. While levels of the oxidative metabolites are correlated with CYP6G1 expression, nitro-reduced metabolites are not, raising the question of how these metabolites are produced. Some IMI metabolites are known to be toxic, making their fate within the insect a second question of interest. These questions have been addressed by coupling the genetic tools of gene overexpression and CRISPR gene knock-out with the mass spectrometric technique, the Twin-Ion Method (TIM). Analysing axenic larvae indicated that microbes living within D. melanogaster are largely responsible for the production of the nitro-reduced metabolites. Knock-out of Cyp6g1 revealed functional redundancy, with some metabolites produced by CYP6G1 still detected. IMI metabolism was shown to produce toxic products that are not further metabolized but readily excreted, even when produced in the Central Nervous System (CNS), highlighting the significance of transport and excretion in metabolic resistance.

piRNA-3878 targets P450 (CpCYP307B1) to regulate pyrethroid resistance in Culex pipiens pallens

Piwi-interacting RNAs (piRNAs) are a novel class of noncoding single-strand RNAs. They play an important role in the germ cell maintenance, brain development, epigenetic regulation of cancer, and antiviral function. However, little is known about the relationship between the piRNAs and insecticide resistance in mosquitoes. In this study, we reported that piRNA-3878 was related with pyrethroid resistance in Culex pipiens pallens. The expression level of piRNA-3878 was lower in both laboratory and field-collected deltamethrin-resistant (DR) strains. Overexpression of piRNA-3878 increased the susceptibility of the DR strain, while inhibiting the expression of piRNA-3878 in DS strain made the mosquitoes more resistant to deltamethrin. Furthermore, we identified that CpCYP307B1 was the target of piRNA-3878. The mosquito mortality rate was increased after downregulating the expression of CpCYP307B1. These findings revealed that piRNA-3878 could target CpCYP307B1 to regulate pyrethroid resistance.

Imidacloprid is degraded by CYP353D1v2, a cytochrome P450 overexpressed in a resistant strain of Laodelphax striatellus

BACKGROUND

Cytochrome P450s are associated with the metabolising of a wide range of compounds, including insecticides. CYP353D1v2 has been found to be overexpressed in an imidacloprid-resistant strain of Laodelphax striatellus. Thus, this study was conducted to express CYP353D1v2 in Sf9 cells as a recombinant protein, to assess its ability to metabolise imidacloprid.

RESULTS

Western blot and carbon monoxide difference spectrum analysis indicated that the intact CYP353D1v2 protein had been successfully expressed in Sf9 insect cells. Catalytic activity tests with four traditional P450-activity-probing substrates found that the expressed CYP353D1v2 preferentially metabolised p-nitroanisole, ethoxycoumarin and ethoxyresorufin with specific activities of 32.70, 0.317 and 1.22 pmol min^-1 pmol^-1 protein respectively, but no activity to luciferin-H EGE. The enzyme activity for degrading imidacloprid was tested by measuring substrate depletion and formation of the metabolite. Kinetic parameters for imidacloprid were K_m 5.99 ± 0.95 µm and k_cat 0.03 ± 0.0004 min^-1 . The chromatogram analysis showed clearly the NADPH-dependent depletion of imidacloprid and the formation of an unknown metabolite. The UPLC-MS mass spectrum demonstrated that the metabolite was an oxidative product of imidacloprid, 5-hydroxy-imidacloprid.

CONCLUSION

These results suggest that CYP353D1v2 in L. striatellus is capable of degrading imidacloprid, and that enzyme activity can be evaluated well only by some traditional probing substrates. © 2017 Society of Chemical Industry.

Resistance irrelevant CYP417A2v2 was found degrading insecticide in Laodelphax striatellus

Cytochrome P450 monooxygenases (CYPs) usually overexpressed in resistant strain were found involved in oxidative detoxification of insecticides. In this study, an investigation was conducted to confirm if resistance irrelevant CYPs which were not overexpressed in resistant strain before, were capable of degrading insecticides. Three resistance irrelevant CYPs viz. CYP417A2v2, CYP425A1v2, and CYP4DJ1 from CYP4 family of Laodelphax striatellus were randomly selected for experiments. CYP417A2v2 and CYP425A1v2 were found expressed successfully in Sf9 cell line while CYP4DJ1 was not expressed successfully and out of two expressed CYPs, only CYP417A2v2 showed its efficient catalytic activity. For catalytic activity, three traditional model probe substrates and five insecticides were assayed. For the probe substrates screened, p-nitroanisole and ethoxycoumarin were preferentially metabolized by CYP417A2v2 (specific activity 3.76 ± 1.22 and 1.63 ± 0.37 nmol min-1 mg protein-1, respectively) and they may be potential diagnostic probes for this enzyme. Among insecticides, only imidacloprid was efficiently degraded by CYP417A2v2. Incubation of imidacloprid with CYP417A2v2 of L. striatellus and subsequent HPLC, LC-MS, and MS/MS analysis revealed the formation of imidacloprid metabolites, that is, 4' or 5'hydroxy-imidacloprid by hydroxylation. This result implies the exemption of CYPs character that it is not always, all the CYPs degrading insecticides being selected and overexpressed in resistant strains and the degrading CYPs without mutations to upregulate could be candidates during insecticide resistance evolution. This characterization of individual insect CYPs in insecticide degradation can provide insight for better understand of insecticide resistance development.