Heterologous expression of insect P450 enzymes that metabolize xenobiotics

A down-regulated cytochrome P450 in Neoseiulus barkeri Hughes (Acari: Phytoseiidae) can dechlorinate and hydroxylate chlorpyrifos without producing chlorpyrifos-oxon

Selection of chemical-resistant predatory mites is a good alternative to balance the contradiction between chemical control and biological control. Previously, a resistant strain of Neoseiulus barkeri for chlorpyrifos was obtained. In the current study, two up-regulated (NbCYP3A6, NbCYP3A16) and one down-regulated (NbCYP3A24) P450s were screened through differential expression analysis and other detoxification-related genes such as CCEs, GST, etc. were not found. 3D modelling and molecular docking indicated that the chlorine at position 5 on the pyridine ring of chlorpyrifos, as well as a methyl group, were closest to the heme iron of the enzymes (less than 5 Å). Three active recombinant P450 proteins were heterologously expressed and metabolized with chlorpyrifos in vitro. HPLC assay showed that only NbCYP3A24 could metabolize chlorpyrifos, with a metabolism rate of 21.60 %. Analysis of the m/z of metabolites by LC-MS/MS showed that chlorine at the 5C position of chlorpyrifos was stripped and hydroxylated, whereas chlorpyrifos-oxon, a common product of oxidation by P450, was not found. Knockdown of the NbCYP3A24 gene in the susceptiblestrain did reduce the susceptibility of N. barkeri to chlorpyrifos, suggesting that the biological activity of the metabolite may be similar to chlorpyrifos-oxon, thus enhancing the inhibitory effect on the target.

Comparative Genomics Uncovers the Evolutionary Dynamics of Detoxification and Insecticide Target Genes Across 11 Phlebotomine Sand Flies

Sand flies infect more than 1 million people annually with Leishmania parasites and other bacterial and viral pathogens. Progress in understanding sand fly adaptations to xenobiotics has been hampered by the limited availability of genomic resources. To address this gap, we sequenced, assembled, and annotated the transcriptomes of 11 phlebotomine sand fly species. Subsequently, we leveraged these genomic resources to generate novel evolutionary insights pertaining to their adaptations to xenobiotics, including those contributing to insecticide resistance. Specifically, we annotated over 2,700 sand fly detoxification genes and conducted large-scale phylogenetic comparisons to uncover the evolutionary dynamics of the five major detoxification gene families: cytochrome P450s (CYPs), glutathione-S-transferases (GSTs), UDP-glycosyltransferases (UGTs), carboxyl/cholinesterases (CCEs), and ATP-binding cassette (ABC) transporters. Using this comparative approach, we show that sand flies have evolved diverse CYP and GST gene repertoires, with notable lineage-specific expansions in gene groups evolutionarily related to known xenobiotic metabolizers. Furthermore, we show that sand flies have conserved orthologs of (i) CYP4G genes involved in cuticular hydrocarbon biosynthesis, (ii) ABCB genes involved in xenobiotic toxicity, and (iii) two primary insecticide targets, acetylcholinesterase-1 (Ace1) and voltage gated sodium channel (VGSC). The biological insights and genomic resources produced in this study provide a foundation for generating and testing hypotheses regarding the molecular mechanisms underlying sand fly adaptations to xenobiotics.

The cytochrome P450 subfamilies CYP392A and CYP392D are key players in acaricide metabolism in Tetranychusurticae

The spider mite Tetranychus urticae is a major agricultural pest with a global distribution, extremely diverse host range and a remarkable ability to develop resistance to a wide variety of acaricides. P450 mono-oxygenases have been frequently associated with resistance development in this species. In particular enzymes of the CYP392A-subfamily were shown to metabolize a number of key acaricides, including abamectin, amitraz, fenpyroximate and the active metabolite of pyflubumide. However, transcriptomic studies comparing highly resistant and susceptible populations have often revealed high expression of members of the CYP392D-subfamily, but these have been only poorly studied. Here, we conducted a meta-analysis of gene expression data of 20 populations and identified two key enzymes of this family, CYP392D2 and CYP392D8, whose expression is associated with resistance. We subsequently functionally expressed these enzymes, together with CYP392A11 and CYP392A16 as known metabolizers, and compared their potential to accept a wide diversity of acaricides as substrate. This study overall confirms previous discovered substrates for CYP392A11 and CYP392A16, but also reveals unreported metabolic activity towards new acaricides. These include carbaryl, chlorpyrifos and etoxazole for CYP392A16 and carbaryl, chlorpyrifos and NNI-0711-NH pyflubumide for CYP392A11. For the newly studied CYP392D-family, we show that CYP392D2 metabolizes pyridaben, fenpyroximate, etoxazole and chlorpyrifos, while CYP392D8 metabolizes carbaryl, fenazaquin and tebufenpyrad. Last, we observed that both CYP392A- and CYP392D-subfamily enzymes activate chlorpyrifos to its corresponding oxon. Our study indicates that there is both overlap and specificity in the activity of A- and D-subfamily enzymes against acaricides and model substrates. With the recent advent of highly efficient CRISPR/Cas9 gene editing protocols in T. urticae, the way is now paved to conduct further genetic experiments revealing and quantifying the role of these enzymes in the resistance phenotype in field populations.

Elucidating the detoxification efficacy of Periplaneta americana delta glutathione S-transferase 1 (PaGSTd1) against organophosphates

As an important class of detoxifying enzymes, glutathione S-transferases (GSTs) are pivotal in decreasing insecticide toxicity to insects. Periplaneta americana GSTd1 (PaGSTd1) has been verified as a key enzyme in detoxifying pyrethroid insecticides, but its detoxification capability against a broader spectrum of insecticides has never been investigated. It is revealed that PaGSTd1 expression showed a rapid and significant increase upon exposure to various insecticides (organophosphates, neonicotinoids, and fipronil). Subsequent in vitro metabolic assays indicated that organophosphates, particularly chlorpyrifos-methyl, can be effectively metabolized by PaGSTd1. Further knockdown of PaGSTd1 via RNA interference significantly heightened the susceptibility of P. americana to chlorpyrifos-methyl, underscoring the enzyme's key role in detoxifying chlorpyrifos-methyl. Additionally, this study confirmed that PaGSTd1 cannot mitigate insecticide toxicity through countering oxidative stress. Collectively, these findings elucidate the involvement of PaGSTd1 in the detoxification processes for organophosphates, offering a comprehensive insight into the metabolic mechanisms mediated by GSTs in P. americana. This research provides a foundational understanding for managing GSTs-mediated metabolic resistance in this species, which is crucial for effective pest control strategies.

Trial and error: New insights into recombinant expression of membrane-bound insect cytochromes P450 in Escherichia coli systems

Insect cytochromes P450 (CYP450s) are key enzymes responsible for a wide array of oxidative transformations of both endogenous and exogenous substrates. However, there is currently no a universal guideline established for heterologous expression of membrane-bound CYP450s, which hampers their downstream biochemical and structural studies. In this study, we conducted large-scale screening of protein overexpression in Escherichia coli using 71 insect CYP450 sequences and optimized the expression of a difficult-to-express CYP450 (CYP6HX3) using eight different optimizations, including selection of host strains and expression vectors, alternative of leader signal peptides, and N-terminal modifications. We confirmed that 1) Only insect CYP450s belonging to the CYP347 family could be expressed with N-terminal fusion of ompA2+ signal peptide in E. coli expression system. 2) E. coli Lemo 21 (DE3) effectively improved the expression of CYP6HX3 in the plasma membrane. 3) A brick-red appearance occurred frequently in the expressed thallus or membrane proteins, but this phenomenon could not necessarily indicate successful overexpression of target CYP450s. These findings provide new insights into the recombinant expression of insect CYP450s in E. coli systems and will facilitate the theoretical approaches for functional expression and production of eukaryotic CYP450s.

Nicotinamide deficiency promotes imidacloprid resistance via activation of ROS/CncC signaling pathway-mediated UGT detoxification in Nilaparvata lugens

Metabolic alternation is a typical characteristic of insecticide resistance in insects. However, mechanisms underlying metabolic alternation and how altered metabolism in turn affects insecticide resistance are largely unknown. Here, we report that nicotinamide levels are decreased in the imidacloprid-resistant strain of Nilaparvata lugens, may due to reduced abundance of the symbiotic bacteria Arsenophonus. Importantly, the low levels of nicotinamide promote imidacloprid resistance via metabolic detoxification alternation, including elevations in UDP-glycosyltransferase enzymatic activity and enhancements in UGT386B2-mediated metabolism capability. Mechanistically, nicotinamide suppresses transcriptional regulatory activities of cap 'n' collar isoform C (CncC) and its partner small muscle aponeurosis fibromatosis isoform K (MafK) by scavenging the reactive oxygen species (ROS) and blocking the DNA binding domain of MafK. In imidacloprid-resistant N. lugens, nicotinamide deficiency re-activates the ROS/CncC signaling pathway to provoke UGT386B2 overexpression, thereby promoting imidacloprid detoxification. Thus, nicotinamide metabolism represents a promising target to counteract imidacloprid resistance in N. lugens.

Glutathione S-transferase directly metabolizes imidacloprid in the whitefly, Bemisia tabaci

The whitefly Bemisia tabaci poses a significant threat to various crops and ornamental plants and causes severe damage to the agricultural industry. Over the past few decades, B. tabaci has developed resistance to several pesticides, including imidacloprid. Therefore, elucidating the mechanism that leads to insecticide detoxification is very important for controlling B. tabaci and managing whitefly resistance to neonicotinoid insecticides. Among insect detoxification enzymes, glutathione S-transferase (GST) is an important phase II detoxification enzyme that helps detoxify exogenous toxic substances. In this study, we cloned the BtGSTz1 gene and observed that its expression level was greater in imidacloprid-resistant populations than sensitive populations of B. tabaci. By silencing BtGSTz1 via RNA interference, we found a significant increase in the mortality of imidacloprid-resistant B. tabaci. Additionally, prokaryotic expression and in vitro metabolism studies revealed that the recombinant BtGSTz1 protein could metabolize 36.36% of the total imidacloprid, providing direct evidence that BtGSTz1 plays a crucial role in the detoxification of imidacloprid. Overall, our study elucidated the role of GSTs in physiological activities related to insecticide resistance, which helps clarify the resistance mechanisms conferred by GSTs and provides useful insights for sustainable integrated pest management.

New insights into chlorantraniliprole metabolic resistance mechanisms mediated by the striped rice borer cytochrome P450 monooxygenases: A case study of metabolic differences

The anthranilic diamide insecticide chlorantraniliprole has been extensively applied to control Lepidoptera pests. However, its overuse leads to the development of resistance and accumulation of residue in the environment. Four P450s (CYP6CV5, CYP9A68, CYP321F3, and CYP324A12) were first found to be constitutively overexpressed in an SSB CAP-resistant strain. It is imperative to further elucidate the molecular mechanisms underlying P450s-mediated CAP resistance for mitigating its environmental contamination. Here, we heterologously expressed these four P450s in insect cells and evaluated their abilities to metabolize CAP. Western blotting and reduced CO difference spectrum tests showed that these four P450 proteins had been successfully expressed in Sf9 cells, which are indicative of active functional enzymes. The recombinant proteins CYP6CV5, CYP9A68, CYP321F3, and CYP324A12 exhibited a preference for metabolizing the fluorescent P450 model probe substrates EC, BFC, EFC, and EC with enzyme activities of 0.54, 0.67, 0.57, and 0.46 pmol/min/pmol P450, respectively. In vitro metabolism revealed distinct CAP metabolic rates (0.97, 0.86, 0.75, and 0.55 pmol/min/pmol P450) and efficiencies (0.45, 0.37, 0.30, and 0.17) of the four recombinant P450 enzymes, thereby elucidating different protein catalytic activities. Furthermore, molecular model docking confirmed metabolic differences and efficiencies of these P450s and unveiled the hydroxylation reaction in generating N-demethylation and methylphenyl hydroxylation during CAP metabolism. Our findings not only first provide new insights into the mechanisms of P450s-mediated metabolic resistance to CAP at the protein level in SSB but also demonstrate significant differences in the capacities of multiple P450s for insecticide degradation and facilitate the evaluation and mitigation of toxic risks associated with CAP application in the environment.

CYP4CS5-mediated thiamethoxam and clothianidin resistance is accompanied by fitness cost in the whitefly Bemisia tabaci

BACKGROUND

Understanding the trade-offs between insecticide resistance and the associated fitness is of particular importance to sustainable pest control. One of the most devastating pest worldwide, the whitefly Bemisia tabaci, has developed resistance to various insecticides, especially the neonicotinoid group. Although neonicotinoid resistance often is conferred by P450s-mediated metabolic resistance, the relationship between such resistance and the associated fitness phenotype remains largely elusive. By gene cloning, quantitative reverse transcription (qRT)-PCR, RNA interference (RNAi), transgenic Drosophila melanogaster, metabolism capacity in vitro and 'two sex-age stage' life table study, this study aims to explore the molecular role of a P450 gene CYP4CS5 in neonicotinoid resistance and to investigate whether such resistance mechanism carries fitness costs in the whitefly.

RESULTS

Our bioassay tests showed that a total of 13 field-collected populations of B. tabaci MED biotype displayed low-to-moderate resistance to thiamethoxam and clothianidin. Compared to the laboratory susceptible strain, we then found that an important P450 CYP4CS5 was remarkably upregulated in the field resistant populations. Such overexpression of CYP4CS5 had a good match with the resistance level among the whitefly samples. Further exposure to the two neonicotinoids resulted in an increase in CYP4CS5 expression. These results implicate that overexpression of CYP4CS5 is closely correlated with thiamethoxam and clothianidin resistance. RNAi knockdown of CYP4CS5 increased mortality of the resistant and susceptible populations after treatment with thiamethoxam and clothianidin in bioassay, but obtained an opposite result when using a transgenic line of D. melanogaster expressing CYP4CS5. Metabolic assays in vitro revealed that CYP4CS5 exhibited certain capacity of metabolizing thiamethoxam and clothianidin. These in vivo and in vitro assays indicate an essential role of CYP4CS5 in conferring thiamethoxam and clothianidin resistance in whitefly. Additionally, our life-table analysis demonstrate that the field resistant whitefly exhibited a prolonged development time, shortened longevity and reduced fecundity compared to the susceptible, suggesting an existing fitness cost as a result of the resistance.

CONCLUSION

Collectively, in addition to the important role of CYP4CS5 in conferring thiamethoxam and clothianidin resistance, this resistance mechanism is associated with fitness costs in the whitefly. These findings not only contribute to the development of neonicotinoids resistance management strategies, but also provide a new target for sustainable whitefly control. © 2023 Society of Chemical Industry.

Comprehensive analysis of the overexpressed cytochrome P450-based insecticide resistance mechanism in Spodoptera litura

Cytochrome P450s play critical roles in the metabolic resistance of insecticides in insects. Previous findings showed that enhanced P450 activity was an important mechanism mediating indoxacarb resistance, and multiple P450 genes were upregulated in indoxacarb resistant strains of Spodoptera litura. However, the functions of these P450 genes in insecticide resistance remain unknown. Here, the P450 inhibitor PBO effectively decreased the resistance of S. litura to indoxacarb. Ten upregulated P450 genes were characterized, all of which were overexpressed in response to indoxacarb induction. Knockdown of nine P450 genes decreased cell viability against indoxacarb, and further silencing of three genes (CYP339A1, CYP340G2, CYP321A19) in larvae enhanced the sensitivity to indoxacarb. Transgenic overexpression of these three genes increased resistance to indoxacarb in Drosophila melanogaster. Moreover, molecular modeling and docking predicted that these three P450 proteins could bind tightly to indoxacarb and N-decarbomethoxylated metabolite (DCJW). Interestingly, these three P450 genes may also mediate cross-resistance to chlorantraniliprole, λ-cyhalothrin and imidacloprid. Additionally, heterologous expression and metabolic assays confirmed that three recombinant P450s could effectively metabolize indoxacarb and DCJW. This study strongly demonstrates that multiple overexpressed mitochondrial and microsomal P450 genes were involved in insecticide resistance in S. litura.

Enhancement of tolerance against flonicamid in Solenopsis invicta (Hymenoptera: Formicidae) through overexpression of CYP6A14

Solenopsis invicta is a main issue in southern China and is causing significant damage to the local ecological environment. The extensive use of insecticides has resulted in the development of tolerance in S. invicta. In our study, ten S. invicta colonies from Sichuan Province exhibited varying degrees of tolerance against flonicamid, with LC50 values from 0.49 mg/L to 8.54 mg/L. The sensitivity of S. invicta to flonicamid significantly increased after treatment with the P450 enzyme inhibitor piperonyl butoxide (PBO). Additionally, the activity of P450 in S. invicta was significantly enhanced after being treated with flonicamid. Flonicamid induced the expression levels of CYP4aa1, CYP9e2, CYP4C1, and CYP6A14. The expression levels of these P450 genes were significantly higher in the tolerant colonies compared to the sensitive colonies, and the relative copy numbers of CYP6A14 in the tolerant colonies were 2.01-2.15 fold. RNAi feeding treatment effectively inhibited the expression of P450 genes, thereby reducing the tolerance of S. invicta against flonicamid. In addition, the overexpression of CYP6A14 in D. melanogaster resulted in reduced sensitivity to flonicamid. Our investigations revealed hydrophobic interactions between flonicamid and seven amino acid residues of CYP6A14, along with the formation of a hydrogen bond between Glu306 and flonicamid. Our findings suggest that flonicamid can effectively control S. invicta and P450 plays a pivotal role in the tolerance of S. invicta against flonicamid. The overexpression of CYP6A14 also increased tolerance to flonicamid.

Overexpression of the F116V allele of CYP9A186 in transgenic Helicoverpa armigera confers high-level resistance to emamectin benzoate

Insect cytochrome P450s play important roles in the detoxification of xenobiotics and the metabolic resistance to insecticides. However, the approach for in vivo validation of the contribution of specific candidate P450s to resistance is still limited in most non-model insect species. Previous studies with heterologous expression and in vitro functional assays have confirmed that a natural substitution (F116V) in the substrate recognition site 1 (SRS1) of the CYP9A186 of Spodoptera exigua is a gain-of-function mutation, which results in detoxification capability of and thus high-level resistance to both emamectin benzoate (EB) and abamectin. In this study, we established an effective piggyBac-based transformation system in the serious agricultural pest Helicoverpa armigera and overexpressed in vivo a resistance P450 allele, CYP9A186-F116V, from another lepidopteran pest Spodoptera exigua. Bioassays showed that transgenic H. armigera larvae expressing CYP9A186-F116V obtained 358-fold and 38.6-fold resistance to EB and abamectin, respectively. In contrast, a transgenic line of Drosophila melanogaster overexpressing this P450 variant only confers ∼20-fold resistance to the two insecticides. This bias towards the resistance level revealed that closely related species might provide a more appropriate cellular environment for gene expression and subsequent toxicokinetics of insecticides. These results not only present an alternative method for in vivo functional characterization of P450s in H. armigera and other phylogenetically close species but also provide a valuable genetic engineering toolkit for the genetic manipulation of H. armigera.

Evolution and functional role prediction of the CYP6DE and CYP6DJ subfamilies in Dendroctonus (Curculionidae: Scolytinae) bark beetles

Dendroctonus-bark beetles are natural components and key ecological agents of coniferous forests. They spend most of their lives under the bark, where they are exposed to highly toxic terpenes present in the oleoresin. Cytochrome P450 (CYP) is a multigene family involved in the detoxification of these compounds. It has been demonstrated that CYP6DE and CYP6DJ subfamilies hydroxylate monoterpenes, whose derivatives can act as pheromone synergist compounds or be pheromones themselves in these insects. Given the diversity and functional role of CYPs, we investigated whether these cytochromes have retained their function throughout the evolution of these insects. To test this hypothesis, we performed a Bayesian phylogenetic analysis to determine phylogenetic subgroups of cytochromes in these subfamilies. Subgroups were mapped and reconciled with the Dendroctonus phylogeny. Molecular docking analyses were performed with the cytochromes of each subgroup and enantiomers of α-pinene and β-pinene, (+)-3-carene, β-myrcene and R-(+)-limonene. In addition, functional divergence analysis was performed to identify critical amino acid sites that influence changes in catalytic site conformation and/or protein folding. Three and two phylogenetic subgroups were recovered for the CYP6DE and CYP6DJ subfamilies, respectively. Mapping and reconciliation analysis showed different gain and loss patterns for cytochromes of each subgroup. Functional predictions indicated that the cytochromes analyzed are able to hydroxylate all monoterpenes; however, they showed preferential affinities to different monoterpenes. Functional divergence analyses indicated that the CYP6DE subfamily has experimented type I and II divergence, whereas the CYP6DJ subfamily has evolved under strong functional constraints. Results suggest cytochromes of the CYP6DE subfamily evolve to reinforce their detoxifying capacity hydroxylating mainly α- and β-pinene to (+) and (-)-trans-verbenol, being the negative enantiomer used as a pheromone by several Dendroctonus species; whereas cytochromes of the CYP6DJ subfamily appear to retain their original function related to the detoxification of these compounds.

20E biosynthesis gene CYP306A1 confers resistance to imidacloprid in the nymph stage of Bemisia tabaci by detoxification metabolism

BACKGROUND

Difference in physiology level between the immature and mature stages of insects likely contribute to different mechanisms of insecticide resistance. It is well acknowledged that insect 20-hydroxyecdysone (20E) plays an important role in many biological processes in the immature stage, whether 20E confers insecticide resistance at this specific stage is still poorly understood. By gene cloning, reverse transcription quantitative real-time PCR, RNA interference (RNAi) and in vitro metabolism experiments, this study aimed to investigate the potential role of 20E-related genes in conferring imidacloprid (IMD) resistance in the immature stage of the whitefly Bemisia tabaci Mediterranean.

RESULTS

After identification of low to moderate IMD resistance in the whitefly, we found CYP306A1 of the six 20E-related genes was overexpressed in the nymph stage of the three resistant strains compared to a laboratory reference susceptible strain, but not in the adult stage. Further exposure to IMD resulted in an increase in CYP306A1 expression in the nymph stage. These results together imply that CYP306A1 may be implicated in IMD resistance in the nymph stage of the whitefly. RNAi knockdown of CYP306A1 increased the mortality of nymphs after treatment with IMD in bioassay, suggesting a pivotal role of CYP306A1 in conferring IMD resistance in the nymph stage. Additionally, our metabolism experiments in vivo showed that the content of IMD reduced by 20% along with cytochrome P450 reductase and heterologously expressed CYP306A1, which provides additional evidence for the important function of CYP306A1 in metabolizing IMD that leads to the resistance.

CONCLUSION

This study uncovers a novel function of the 20E biosynthesis gene CYP306A1 in metabolizing imidacloprid, thus contributing to such resistance in the immature stage of the insect. These findings not only advance our understanding of 20E-mediated insecticide resistance, but also provide a new target for sustainable pest control of global insect pests such as whitefly. © 2023 Society of Chemical Industry.

Recent advances in fungal xenobiotic metabolism: enzymes and applications

Fungi have been extensively studied for their capacity to biotransform a wide range of natural and xenobiotic compounds. This versatility is a reflection of the broad substrate specificity of fungal enzymes such as laccases, peroxidases and cytochromes P450, which are involved in these reactions. This review gives an account of recent advances in the understanding of fungal metabolism of drugs and pollutants such as dyes, agrochemicals and per- and poly-fluorinated alkyl substances (PFAS), and describes the key enzymes involved in xenobiotic biotransformation. The potential of fungi and their enzymes in the bioremediation of polluted environments and in the biocatalytic production of important compounds is also discussed.

Development of an efficient insecticide substrate and inhibitor screening system of insect P450s using fission yeast

Metabolic resistance is one of the most frequent mechanisms of insecticide resistance, characterized by an increased expression of several important enzymes and transporters, especially cytochrome P450s (CYPs). Due to the large number of P450s in pests, determining the precise relationship between these enzymes and the insecticide substrates is a challenge. Herein, we developed a luminescence-based screening system for efficient identification of insecticide substrates and insect P450 inhibitors. We recombinantly expressed Bemisia tabaci CYP6CM1vQ (Bt CYP6CM1vQ) in the fission yeast Schizosaccharomyces pombe and subsequently permeabilized the yeast cells to convert them into "enzyme bags". We exploited these enzyme bags to screen the activity of twelve luciferin substrates and identified Luciferin-FEE as the optimal competing probe that was further used to characterize the metabolism of eight candidate commercial insecticides. Among them, Bt CYP6CM1vQ exhibited notable activity against pymetrozine and imidacloprid. Their binding modes were predicted by homology modeling and molecular docking, revealing the mechanisms of the metabolism. We also tested the inhibitory effect of eight known P450 inhibitors using our system and identified letrozole and 1-benzylimidazole as showing significant activity against Bt CYP6CM1vQ, with IC₅₀ values of 23.74 μM and 1.30 μM, respectively. Their potential to be developed as an insecticide synergist was further proven by an in vitro toxicity assay using imidacloprid-resistant Bemisia tabaci. Overall, our luciferin-based enzyme bag method is capable of providing a robust and efficient screening of insect P450 substrates and, more importantly, inhibitors to overcome the resistance.

Effects of azadirachtin on detoxification-related gene expression in the fat bodies of the fall armyworm, Spodoptera frugiperda

The fall armyworm, Spodoptera frugiperda, has become a worldwide pest and threatens world food production. A previous study indicated that azadirachtin, the most effective botanical insecticide for S. frugiperda, inhibits larval growth of the insect. The effect of azadirachtin on the tissues of the larvae, however, remains to be determined. In this study, the effects of azadirachtin on the structure of fat bodies were analyzed. Comparative transcriptomic analysis was conducted between controls and samples treated with 0.1 μg/g azadirachtin for 7 days to explore potential relevant mechanisms. The expression of 5356 genes was significantly affected after azadirachtin treatment, with 3020 up-regulated and 2336 down-regulated. Among them, 137 encode detoxification enzymes, including 53 P450s, 20 GSTs, 27 CarEs, 16 UGTs, and 12 ABC transporters. Our results indicated that azadirachtin could destroy fat body structure and change the mRNA levels of detoxification-related genes. The up-regulated genes encoding detoxification enzymes might be related to detoxifying azadirachtin. Our results elucidate a preliminary mechanism of azadirachtin detoxification in the fat bodies of S. frugiperda larvae.

Performance of Pyrethroid-Neonicotinoid Mixture Formulations Against Field-Collected Strains of the Tropical Bed Bug (Hemiptera: Cimicidae) on Different Substrates

The residual performance of two pyrethroid-neonicotinoid mixture formulations: Temprid SC (10.5% beta-cyfluthrin and 21% imidacloprid) and Tandem (3.5% lambda-cyhalothrin and 11.6% thiamethoxam) on two substrates (glass and filter paper) against eight pyrethroid-resistant strains (BM-MY, BP-MY, CH-MY, GL-MY, KL-MY, SAJ-MY, TT-MY, and QLD-AU) of the tropical bed bug, Cimex hemipterus (F.) (Hemiptera: Cimicidae) collected from Malaysia, and Australia were evaluated. The aging effect of treatment residues on glass was also investigated. A susceptible C. lectularius L. strain (Monheim) was used for comparison. Temprid SC showed varying levels of performance against all C. hemipterus strains: TT-MY (PR50 = 6.5-fold, high performance), BM-MY, GL-MY, SAJ-MY, and QLD-AU (12.8-21.6-fold, moderate performance), BP-MY, and KL-MY (48.2-49-fold, poor performance), CH-MY (128.2-fold, very poor performance). On the other hand, Tandem displayed high performance against all C. hemipterus strains (1.8-8.3-fold). Tandem caused faster mortality than Temprid SC for all strains. Temprid SC and Tandem residues killed C. hemipterus significantly faster on glass than filter paper. Compared with fresh residues, the efficacy of Temprid SC residues significantly declined after one week of aging, while the effectiveness of Tandem residues declined after two weeks of aging. Further investigations using the topical assay method with a diagnostic dose of imidacloprid found two strains (CH-MY and GL-MY) resistant to imidacloprid. The six other strains (BM-MY, BP-MY, KL-MY, SAJ-MY, TT-MY, and QLD-AU) were susceptible.

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.

Toxicological effects caused by environmental relevant concentrations of ketoconazole in Chironomus sancticaroli (Diptera, Chironomidae) larvae evaluated by oxidative stress biomarkers

Ketoconazole (KTZ), a broad-spectrum fungicidal drug, has been a significant problem in recent decades due to its toxic action on non-target aquatic organisms. Thus, the present study aimed to evaluate determine the effects that environmental relevant concentration of the commercial formulation of KTZ can exert on benthic macroinvertebrates, more specifically on larvae of the insect Chironomus sancticaroli. Acute toxicity tests with KTZ indicated lethal concentration (LC₅₀) of 9.9 μg/L. Analyses of prolonged exposure to KTZ (chronic toxicity) indicated an increase in the rate of mentum deformity by approximately 3 times at concentrations of 0.6 and 2.4 μg/L. All biomarkers analyzed showed an increase after exposure to KTZ (0.6 and 2.4 μg/L), with average values of 115 % for superoxide dismutase (SOD), 63 % for catalase (CAT), 111 % for glutathione S-transferase (GST) and 59 % for malonaldehyde (MDA) in C. sancticaroli larvae. Thus, the toxic effects on survival, development (length and weight), mentum and redox responses caused by commercial KTZ in low concentrations were observed on C. sancticaroli larvae. In addition, the results suggest that biochemical biomarkers can be used for studies involving environmental disturbances.

Tolerance to dietary linalool primarily involves co-expression of cytochrome P450s and cuticular proteins in Pagiophloeus tsushimanus (Coleoptera: Curculionidae) larvae using SMRT sequencing and RNA-seq

BACKGROUND

Pagiophloeus tsushimanus (Coleoptera: Curculionidae), an emerging forest pest exclusively infesting camphor trees, has recently caused severe ecological and economic damage in localized areas in China. Its population outbreak depends largely on the capacity to overcome the pressure of terpenoid-derived metabolites (e.g. linalool) from camphor trees. At present, the molecular basis of physiological adaptation of P. tsushimanus to dietary linalool is poorly understood, and there is no available reference genome or transcriptome.

RESULTS

Herein, we constructed the transcriptome profiling of P. tsushimanus larvae reared on linalool-infused diets using RNA sequencing and single-molecule real-time sequencing. A total of 20,325 high-quality full-length transcripts were identified as a reference transcriptome, of which 14,492 protein-coding transcripts including 130 transcription factors (TFs), and 5561 long non-coding RNAs (lncRNAs) were detected. Also, 30 alternative splicing events and 8049 simple sequence repeats were captured. Gene ontology enrichment of differential expressed transcripts revealed that overall up-regulation of both cytochrome P450s (CYP450s) and cuticular proteins (CPs), was the primary response characteristic against dietary linalool. Other physiological effects possibly caused by linalool exposure, such as increase in Reactive Oxygen Species (ROS) and hormetic stimulation, were compensated by a handful of induced genes encoding antioxidases, heat shock proteins (HSPs), juvenile hormone (JH) epoxide hydrolases, and digestive enzymes. Additionally, based on co-expression networks analysis, a diverse array of hub lncRNAs and TFs co-expressed with CYP450s and CPs were screened as the potential gene regulators. Temporal expression of candidate transcripts determined by quantitative real-time PCR also indicated a cooperative relationship between the inductions of CYP450s and CPs upon exposure to linalool.

CONCLUSIONS

Our present study provides an important transcriptome resource of P. tsushimanus, and lays a valuable foundation for understanding how this specialist pest copes with chemical challenges in its specific host environments.

Functional validation of CYP304A1 associated with haedoxan A detoxification in Aedes albopictus by RNAi and transgenic drosophila

BACKGROUND

Insect cytochrome P450 monooxygenases play important roles in the detoxification metabolism of endogenous and exogenous compounds. Haedoxan A (HA) from Phryma leptostachya L. is a highly efficient natural pesticide used to control houseflies and mosquitos. CYP4C21 and CYP304A1 were previously demonstrated to be transcriptionally increased in Aedes albopictus in response to HA exposure, but their involvement in HA metabolism is unknown.

RESULTS

Our data showed that CYP304A1 expression levels in A. albopictus were highest in third-instar larvae, and the expression level of CYP4C21 decreased significantly with the growth of instars, with the lowest occurring in the pupal stage. Compared with the control, the silencing of CYP304A1 and CYP4C21 genes by chitosan nanoparticle-mediated RNA interference could deplete 58.2% and 54.0% of the expression of corresponding genes, respectively. The bioassay data showed that knocking down the expression of CYP304A1 increased the mortality of A. albopictus when exposed to HA at LC₃₀ and LC₅₀ doses, but did not significantly increase mortality after silencing CYP4C21. Our data demonstrated that CYP304A1, but not CYP4C21, may be involved in HA detoxification. Moreover, the resistance ratio of CYP304A1 overexpressing flies was approximately 2-fold higher than that of the control line. The metabolized product of HA by CYP304A1 needs to be further confirmed by in vitro expression.

CONCLUSION

This finding showed that inducibility was not always linked to detoxifying capabilities, and enhanced our understanding of the molecular basis of HA metabolic detoxification in A. albopictus. © 2022 Society of Chemical Industry.

Genome-Wide Identification of P450 Genes in Chironomid Propsilocerus akamusi Reveals Candidate Genes Involved in Gut Microbiota-Mediated Detoxification of Chlorpyrifos

Chironomids commonly dominate macroinvertebrate assemblages in aquatic habitats and these non-biting midges are known for their ability to tolerate contaminants. Studies regarding the interplay between gut microbiota and host detoxification ability is currently a point of interest. Cytochrome P450s (P450s) are critical metabolic enzymes in which a subset is involved in xenobiotic detoxification. In this study, we first conducted an integrated global investigation of P450s based on the whole genomic sequence of Propsilocerus akamusi and retrieved a series of 64 P450 genes which were further classified into 4 clans and 25 families on the basis of phylogenetic relationships. With assistance of RNA-Seq and RT-qPCR validation, the expression profile of screened PaP450s in guts was compared between chlorpyrifos-challenged larvae with deficient gut microbiota (GD) and those with a conventional gut community (CV). An increasing prevalence of chlorpyrifos from sublethal to lethal dosages induced a greater mortality rate of individuals coupled with remarkable downregulation of 14 P450s in GD larval guts when compared to CV ones. Moreover, it turned out that the decreased level of PaCYP3998B1 and PaCYP3987D1 might imply impaired host endogenous detoxification capability potentiated by gut dysbiosis, reflected by a remarkably severe mortality in GD larvae treated with lethal chlorpyrifos. Collectively, our study unveiled candidate P450 genes that might be mediated by gut symbionts in chlorpyrifos-challenged P. akamusi larvae, possibly facilitating further understanding of the detoxified mechanism that chironomids might employ to alleviate poisonousness.

Single amino acid variations drive functional divergence of cytochrome P450s in Helicoverpa species

Divergence of gene function is a hallmark of evolution, but assessing such divergence in one species or between species requires information on functional alterations of the alleles and homologs. Here, we explore the functional divergence of two paralogs, CYP6AE19 and CYP6AE20, from Helicoverpa armigera, and two close orthologs, CYP6B8 and CYP6B7, from two related species (Helicoverpa zea and H. armigera); although there is high sequence identity within each pair of enzymes, the latter P450 of each pair has lost metabolic competence towards the plant allelochemical xanthotoxin. Multiple chimeric and single/double site mutants were created by exchanging the diverse substrate recognition sites (SRSs) and amino acids within each pair of P450s. Heterologous expression in Sf9 cells and in vitro metabolism studies showed that the exchange of SRS4 swapped the activity of CYP6AE19 and CYP6AE20, and subsequent site-directed mutagenesis demonstrated that the CYP6AE20 V318M substitution causes a gain-of-function towards xanthotoxin. Meanwhile, a single amino acid substitution (L489P) in SRS6 was found to swap activity between the CYP6B orthologs. Sequence alignments of CYP6AE paralogs and all reported insect xanthotoxin-metabolizing P450s suggest M318 and P489 are essential for the catalytic activities of CYP6AE paralogs and CYP6B orthologs, respectively, but P450s in different subfamilies may have different mechanisms towards the same substrate. Our findings demonstrate that a single amino acid substitution can suffice to alter substrate metabolism and this functional divergence resulting from natural mutations will help to further our understanding of the process of natural selection of P450 genes and their role in insect-host plant interactions.

Phylogenomic and functional characterization of an evolutionary conserved cytochrome P450-based insecticide detoxification mechanism in bees

Bee pollinator pesticide risk assessment is a regulatory requirement for pesticide registration and is largely based on experimental data collected for surrogate species such as the western honeybee. Recently, CYP9Q3, a honeybee cytochrome P450 enzyme, has been shown to efficiently detoxify certain insecticides such as the butenolide flupyradifurone and the neonicotinoid thiacloprid. Here we analyzed genomic data for 75 bee species and demonstrated by the recombinant expression of 26 CYP9Q3 putative functional orthologs that this detoxification principle is an evolutionary conserved mechanism across bee families. Our toxicogenomics approach has the potential to inform pesticide risk assessment for nonmanaged bee species that are not accessible for acute toxicity testing.

The regulatory process for assessing the risks of pesticides to bees relies heavily on the use of the honeybee, Apis mellifera, as a model for other bee species. However, the validity of using A. mellifera as a surrogate for other Apis and non-Apis bees in pesticide risk assessment has been questioned. Related to this line of research, recent work on A. mellifera has shown that specific P450 enzymes belonging to the CYP9Q subfamily act as critically important determinants of insecticide sensitivity in this species by efficiently detoxifying certain insecticide chemotypes. However, the extent to which the presence of functional orthologs of these enzymes is conserved across the diversity of bees is unclear. Here we used a phylogenomic approach to identify > 100 putative CYP9Q functional orthologs across 75 bee species encompassing all major bee families. Functional analysis of 26 P450s from 20 representative bee species revealed that P450-mediated detoxification of certain systemic insecticides, including the neonicotinoid thiacloprid and the butenolide flupyradifurone, is conserved across all major bee pollinator families. However, our analyses also reveal that CYP9Q-related genes are not universal to all bee species, with some Megachilidae species lacking such genes. Thus, our results reveal an evolutionary conserved capacity to metabolize certain insecticides across all major bee families while identifying a small number of bee species where this function may have been lost. Furthermore, they illustrate the potential of a toxicogenomic approach to inform pesticide risk assessment for nonmanaged bee species by predicting the capability of bee pollinator species to break down synthetic insecticides.

Structural Modeling of Drosophila melanogaster Gut Cytochrome P450s and Docking Comparison of Fruit Fly Gut and Human Cytochrome P450s

Drosophila melanogaster is a prominent model organism in developmental biology research and in studies related to pathophysiological conditions like cancer and Alzheimer's disease. The fruit fly gut contains several cytochrome P450s (CYP450s) which have central roles in Drosophila development and in the normal physiology of the gut. Since the crystal structures of these proteins have not been deciphered yet, we modeled the structure of 29 different D. melanogaster gut CYP450s using Prime (Schrödinger). The sequences of chosen D. melanogaster gut CYP450s were compared with that of their human counterparts. The common gut (and liver) microsomal CYP450s in humans were chosen for structural comparison to find the homology and identity % of D. melanogaster CYPs with that of their human counterparts. The modeled structures were validated using PROCHECK and the best fit models were used for docking several known human pharmacological agents/drugs to the modeled D. melanogaster gut CYP450s. Based on the binding affinities (ΔG values) of the selected drug molecules with the modeled fly gut CYPs, the plausible differences in metabolism of the prominent drugs in humans and fly were projected. The gut is involved in absorption of oral drugs/pharmacological agents and hence, upregulation of intestinal CYP450 and their reactions with endobiotics and xenobiotics is envisaged. The insights gleaned from this work can validate D. melanogaster as a model organism for studying intestinal drug metabolism, particularly in the context of a) toxicology of pharmacological agents to the gut cells and b) how gut P450 metabolites/products can influence gut homeostasis. This work can help establish a platform for further in vitro investigations on how intestinal CYP450 metabolism can influence gut health. The data from this work can be used for further in silico studies and this work can serve as a platform for future in vitro investigations on intestinal CYP450-mediated metabolism of endo- and xeno-biotics in D. melanogaster.

A mechanism-based approach unveils metabolic routes potentially mediating chlorantraniliprole synergism in honey bees, Apis mellifera L., by azole fungicides

BACKGROUND

Almond production in California is an intensively managed agroecosystem dependent on managed pollination by honey bees, Apis mellifera L. A recent laboratory study reported synergism in honey bees between chlorantraniliprole, a common diamide insecticide used in almond orchards, and the fungicide propiconazole. Indeed, there is an emerging body of evidence that honey bee cytochrome P450 monooxygenases of the CYP9Q subfamily are involved in the detoxification of insecticides across a diverse range of chemical classes. The objective of the present study was to unveil the molecular background of the described synergism and to explore the potential role of CYP9Q enzymes in diamide detoxification.

RESULTS

Our study confirmed the previously reported synergistic potential of propiconazole on chlorantraniliprole in acute contact toxicity bioassays, whereas no synergism was observed for flubendiamide. Fluorescence-based biochemical assays revealed an interaction of chlorantraniliprole, but not flubendiamide, with functionally expressed CYP9Q2 and CYP9Q3. These findings were validated by an increased chlorantraniliprole tolerance of transgenic Drosophila lines expressing CYP9Q2/3, and an analytically confirmed oxidative metabolism of chlorantraniliprole by recombinantly expressed enzymes. Furthermore, we showed that several triazole fungicides used in almond orchards, including propiconazole, were strong nanomolar inhibitors of functionally expressed honey bee CYP9Q2 and CYP9Q3, whereas other fungicides such as iprodione and cyprodinil did not inhibit these enzymes.

CONCLUSION

Honey bee CYP9Q enzymes are involved in chlorantraniliprole metabolism and inhibited by triazole fungicides possibly leading to synergism in acute contact toxicity bioassays. Our mechanistic approach has the potential to inform tier I honey bee pesticide risk assessment.

Biochemical profiling of functionally expressed CYP6P9 variants of the malaria vector Anopheles funestus with special reference to cytochrome b5 and its role in pyrethroid and coumarin substrate metabolism

Cytochrome P450 monooxygenases (P450s) are well studied enzymes catalyzing the oxidative metabolism of xenobiotics in insects including mosquitoes. Their duplication and upregulation in agricultural and public health pests such as anopheline mosquitoes often leads to an enhanced metabolism of insecticides which confers resistance. In the laboratory strain Anopheles funestus FUMOZ-R the duplicated P450s CYP6P9a and CYP6P9b are highly upregulated and proven to confer pyrethroid resistance. Microsomal P450 activity is regulated by NADPH cytochrome P450 oxidoreductase (CPR) required for electron transfer, whereas the modulatory role of cytochrome b₅ (CYB5) on insect P450 activity is less clear. In previous studies CYP6P9a and CYP6P9b were recombinantly expressed in tandem with An. gambiae CPR using E. coli-expression systems and CYB5 added to the reaction mix to enhance activity. However, the precise role of CYB5 on substrate turn-over when combined with CYP6P9a and CYP6P9b remains poorly investigated, thus one objective of our study was to address this knowledge gap. In contrast to the CYP6P9 variants, the expression levels of both CYB5 and CPR were not upregulated in the pyrethroid resistant FUMOZ-R strain when compared to the susceptible FANG strain, suggesting no immediate regulatory role of these genes in pyrethroid resistance in FUMOZ-R. Here, for the first time we recombinantly expressed CYP6P9a and CYP6P9b from An. funestus in a baculovirus expression system using High-5 insect cells. Co-expression of each enzyme with CPR from either An. gambiae or An. funestus did not reveal noteworthy differences in catalytic capacity. Whereas the co-expression of An. funestus CYB5 - tested at different multiplicity of infection (MOI) ratios - resulted in a significantly higher metabolization of coumarin substrates as measured by fluorescence assays. This was confirmed by Michaelis-Menten kinetics using the most active substrate, 7-benzyloxymethoxy-4-trifluoromethylcoumarin (BOMFC). We observed a similar increase in coumarin substrate turnover by adding human CYB5 to the reaction mix. Finally, we compared by UPLC-MS/MS analysis the depletion rate of deltamethrin and the formation of 4'OH-deltamethrin by recombinantly expressed CYP6P9a and CYP6P9b with and without CYB5 and detected no difference in the extent of deltamethrin metabolism. Our results suggest that co-expression (or addition) of CYB5 with CYP6P9 variants, recombinantly expressed in insect cells, can significantly enhance their metabolic capacity to oxidize coumarins, but not deltamethrin.

Functionally characterized arthropod pest and pollinator cytochrome P450s associated with xenobiotic metabolism

The cytochrome P450 family (P450s) of arthropods includes diverse enzymes involved in endogenous essential physiological functions and in the oxidative metabolism of xenobiotics, insecticides and plant allelochemicals. P450s can also establish insecticide selectivity in bees and pollinators. Several arthropod P450s, distributed in different phylogenetic groups, have been associated with xenobiotic metabolism, and some of them have been functionally characterized, using different in vitro and in vivo systems. The purpose of this review is to summarize scientific publications on arthropod P450s from major insect and mite agricultural pests, pollinators and Papilio sp, which have been functionally characterized and shown to metabolize xenobiotics and/or their role (direct or indirect) in pesticide toxicity or resistance has been functionally validated. The phylogenetic relationships among these P450s, the functional systems employed for their characterization and their xenobiotic catalytic properties are presented, in a systematic approach, including critical aspects and limitations. The potential of the primary P450-based metabolic pathway of target and non-target organisms for the development of highly selective insecticides and resistance-breaking formulations may help to improve the efficiency and sustainability of pest control.

The Role of Cytochrome P450s in Insect Toxicology and Resistance

Insect cytochrome P450 monooxygenases (P450s) perform a variety of important physiological functions, but it is their role in the detoxification of xenobiotics, such as natural and synthetic insecticides, that is the topic of this review. Recent advances in insect genomics and postgenomic functional approaches have provided an unprecedented opportunity to understand the evolution of insect P450s and their role in insect toxicology. These approaches have also been harnessed to provide new insights into the genomic alterations that lead to insecticide resistance, the mechanisms by which P450s are regulated, and the functional determinants of P450-mediated insecticide resistance. In parallel, an emerging body of work on the role of P450s in defining the sensitivity of beneficial insects to insecticides has been developed. The knowledge gained from these studies has applications for the management of P450-mediated resistance in insect pests and can be leveraged to safeguard the health of important beneficial insects.

Involvement of CYP2 and mitochondrial clan P450s of Helicoverpa armigera in xenobiotic metabolism

Insect CYP2 and mitochondrial clan P450s are relatively conserved genes encoding enzymes generally thought to be involved in biosynthesis or metabolism of endobiotics. However, emerging evidence argues they have potential roles in chemical defense as well, but their actual detoxification functions remain largely unknown. Here, we focused on the full complement of 8 CYP2 and 10 mitochondrial P450s in the generalist herbivore, Helicoverpa armigera. Their varied spatiotemporal expression profiles were analyzed and reflected their specific functions. For functional study of the mitochondrial clan P450s, the redox partners, adrenodoxin reductase (AdR) and adrenodoxin (Adx), were identified from genomes of eight insects and an efficient in vitro electron transfer system of mitochondrial P450 was established by co-expression with Adx and AdR of H. armigera. All CYP2 clan P450s and 8 mitochondrial P450s were successfully expressed in Sf9 cells and compared functionally. In vitro metabolism assays showed that two CYP2 clan P450s (CYP305B1 and CYP18A1) and CYP333B3 (mito clan) could epoxidize aldrin to dieldrin, while CYP305B1 and CYP339A1 (mito clan) have limited but significant hydroxylation capacities to esfenvalerate. CYP303A1 of the CYP2 clan exhibits high metabolic efficiency to 2-tridecanone. Screening the xenobiotic metabolism competence of CYP2 and mitochondrial clan P450s not only provides new insights on insect chemical defense but also can give indications on their physiological functions in H. armigera and other insects.

Identification and characterization of CYPs induced in the Drosophila antenna by exposure to a plant odorant

Members of the cytochrome p450 (CYP) enzyme family are abundantly expressed in insect olfactory tissues, where they are thought to act as Odorant Degrading Enzymes (ODEs). However, their contribution to olfactory signaling in vivo is poorly understood. This is due in part to the challenge of identifying which of the dozens of antennal-expressed CYPs might inactivate a given odorant. Here, we tested a high-throughput deorphanization strategy in Drosophila to identify CYPs that are transcriptionally induced by exposure to odorants. We discovered three CYPs selectively upregulated by geranyl acetate using transcriptional profiling. Although these CYPs are broadly expressed in the antenna in non-neuronal cells, electrophysiological recordings from CYP mutants did not reveal any changes in olfactory neuron responses to this odorant. Neurons were desensitized by pre-exposing flies to the odorant, but this effect was similar in CYP mutants. Together, our data suggest that the induction of a CYP gene by an odorant does not necessarily indicate a role for that CYP in neuronal responses to that odorant. We go on to show that some CYPs have highly restricted expression patterns in the antenna, and suggest that such CYPs may be useful candidates for further studies on olfactory CYP function.

Pyrethroid metabolism by eleven Helicoverpa armigera P450s from the CYP6B and CYP9A subfamilies

Lepidopteran P450s of the CYP6B and CYP9A subfamilies are thought to play important roles in host plant adaptation and insecticide resistance. An increasing number of paralogs and orthologs with high levels of sequence identity have been found in these subfamilies by mining recent genome projects. However, the biochemical function of most of them remains unknown. A better understanding of the evolution of P450 genes and of the catalytic competence of the enzymes they encode is needed to facilitate studies of host plant use and insecticide resistance. Here, we focused on the full complement of CYP6B (4 genes) and CYP9A (7 genes) in the generalist herbivore, Helicoverpa armigera. These P450s were heterologously expressed in Sf9 cells and compared functionally. In vitro assays showed that all CYP6B and CYP9A P450s can metabolize esfenvalerate efficiently, except for the evolutionarily divergent CYP6B43. A new 2'-hydroxy-metabolite of esfenvalerate was identified and found to be the main metabolite produced by CYP9A12. All tested P450s showed only low induction responses to esfenvalerate. To put these results from H. armigera P450s in perspective, 158 complete CYP6B and 100 complete CYP9A genes from 34 ditrysian species were manually curated. The CYP9A subfamily was more widespread than the CYP6B subfamily and the latter showed dramatic gains and losses, with ten species lacking CYP6B genes. Two adjacent CYP6B loci were found on chromosome 21, with different fates during the evolution of Lepidoptera. The diversity and functional redundancy of CYP6B and CYP9A genes challenge resistance management and pest control strategies as many P450s are available to insects to cope with chemical stresses they encounter.

Pyrethrin-resembling pyrethroids are metabolized more readily than heavily modified ones by CYP9As from Helicoverpa armigera

The cotton bollworm, Helicoverpa armigera, is a polyphagous pest threatening many economically important crops worldwide. Until recently, synthetic pyrethroids remain in wide use for controlling pest insects including the cotton bollworm. Understanding the metabolic mechanism of pyrethroids in a given pest can provide significant implication for a smart choice of insecticides, and such information is useful for the development of novel selective and safe insecticides. In this study, we used complexes of recombinant H. armigera cytochrome P450 CYP9A and NADPH-dependent cytochrome P450 reductase to investigate the capacity of three CYP9A paralogs in the transformation of seven structurally different pyrethroids by metabolism assays. The results showed that the three paralogous CYP9As were able to metabolize multiple pyrethroids. Interestingly, all the three CYP9As transformed pyrethrin-resembling pyrethroids (e.g. bioallethrin) more efficiently than the heavily modified ones (e.g. bifenthrin). These findings suggest that herbivorous insects can cope with synthetic insecticides using their physiological systems that initially evolved to survive exposure to the defensive chemicals in their host plants, adding support to the pre-adaptation hypothesis.

A toxicogenomics approach reveals characteristics supporting the honey bee (Apis mellifera L.) safety profile of the butenolide insecticide flupyradifurone

Flupyradifurone, a novel butenolide insecticide, selectively targets insect nicotinic acetylcholine receptors (nAChRs), comparable to structurally different insecticidal chemotypes such as neonicotinoids and sulfoximines. However, flupyradifurone was shown in acute toxicity tests to be several orders of magnitude less toxic to western honey bee (Apis mellifera L.) than many other insecticides targeting insect nAChRs. The underlying reasons for this difference in toxicity remains unknown and were investigated here. Pharmacokinetic studies after contact application of [¹⁴C]flupyradifurone to honey bees revealed slow uptake, with internalized compound degraded into a few metabolites that are all practically non-toxic to honey bees in both oral and contact bioassays. Furthermore, receptor binding studies revealed a lack of high-affinity binding of these metabolites to honey bee nAChRs. Screening of a library of 27 heterologously expressed honey bee cytochrome P450 enzymes (P450s) identified three P450s involved in the detoxification of flupyradifurone: CYP6AQ1, CYP9Q2 and CYP9Q3. Transgenic Drosophila lines ectopically expressing CYP9Q2 and CYP9Q3 were significantly less susceptible to flupyradifurone when compared to control flies, confirming the importance of these P450s for flupyradifurone metabolism in honey bees. Biochemical assays using the fluorescent probe substrate 7-benzyloxymethoxy-4-(trifluoromethyl)-coumarin (BOMFC) indicated a weak, non-competitive inhibition of BOMFC metabolism by flupyradifurone. In contrast, the azole fungicides prochloraz and propiconazole were strong nanomolar inhibitors of these flupyradifurone metabolizing P450s, explaining their highly synergistic effects in combination with flupyradifurone as demonstrated in acute laboratory contact toxicity tests of adult bees. Interestingly, the azole fungicide prothioconazole is only slightly synergistic in combination with flupyradifurone - an observation supported by molecular P450 inhibition assays. Such molecular assays have value in the prediction of potential risks posed to bees by flupyradifurone mixture partners under applied conditions. Quantitative PCR confirmed the expression of the identified P450 genes in all honey bee life-stages, with highest expression levels observed in late larvae and adults, suggesting honey bees have the capacity to metabolize flupyradifurone across all life-stages. These findings provide a biochemical explanation for the low intrinsic toxicity of flupyradifurone to honey bees and offer a new, more holistic approach to support bee pollinator risk assessment by molecular means.

Pesticide risk assessment at the molecular level using honey bee cytochrome P450 enzymes: A complementary approach

Honey bee (Apis mellifera) first-tier pesticide risk assessment is largely based on standardized laboratory toxicity bioassays after both acute and chronic exposure. Recent research on honey bee cytochrome P450 monooxygenases (P450s) uncovered CYP9Q3 as the molecular determinant mediating neonicotinoid insecticide selectivity and explaining why certain neonicotinoids such as thiacloprid show > 1000-fold lower acute toxicity than others (e.g. imidacloprid). Here this knowledge is leveraged for mechanistic risk assessment at the molecular level using a fluorescence-based high-throughput in vitro assay, predicting the interaction of diverse pesticidal chemotypes, including azole fungicides, with recombinantly expressed honey bee CYP9Q enzymes, known to metabolize thiacloprid, acetamiprid and tau-fluvalinate. Some azole fungicides were shown to be synergistic in combination with certain insecticides, including neonicotinoids and pyrethroids, whereas others such as prothioconazole were not. We demonstrate that biochemical CYP9Q2/CYP9Q3 inhibition data of azoles revealed a striking correlation with their synergistic potential at the organismal level, and even allow to explain combined toxicity effects observed for tank mixtures under field conditions. Our novel toxicogenomics-based approach is designed to complement existing methods for pesticide risk assessment with unprecedented screening capacity, by utilizing honey bee P450 enzymes known to confer pesticide selectivity, in order to biochemically address issues of ecotoxicological concern.