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

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.

CYP4CL2 Confers Metabolic Resistance to Pyridaben in the Citrus Pest Mite Panonychus citri

The citrus red mite Panonychus citri has developed strong resistance to acaricides. Cytochrome P450 monooxygenases (P450s) can detoxify pesticides and are involved in pesticide resistance in many insects. Here, a pyridaben-resistant P. citri strain showed cross-resistance to cyenopyrafen, bifenazate, fenpyroximate, and tolfenpyrad. Piperonyl butoxide, a P450 inhibitor, significantly increased the toxicity of pyridaben to resistant (Pyr_Rs) and susceptible (Pyr_Control) P. citri strains. P450 activity was significantly higher in Pyr_Rs than in Pyr_Control. Analyses of RNA-Seq data identified a P450 gene (CYP4CL2) that is potentially involved in pyridaben resistance. Consistently, it was up-regulated in two field-derived resistant populations (CQ_WZ and CQ_TN). RNA interference-mediated knockdown of CYP4CL2 significantly decreased the pyridaben resistance in P. citri. Transgenic Drosophila melanogaster expressing CYP4CL2 showed increased pyridaben resistance. Molecular docking analysis showed that pyridaben could bind to several amino acids at substrate recognition sites in CYP4CL2. These findings shed light on P450-mediated pyridaben resistance in pest mites.

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.

CYP321A Subfamily P450s Contribute to the Detoxification of Phytochemicals and Pyrethroids in Spodoptera litura

Although the induction of cytochrome P450 monooxygenases involved in insect detoxification has been well documented, the underlying regulatory mechanisms remain obscure. In Spodoptera litura, CYP321A subfamily members were effectively induced by exposure to flavone, xanthotoxin, curcumin, and λ-cyhalothrin, while knockdown of the CYP321A genes increased larval susceptibility to these xenobiotics. Homology modeling and molecular docking analyses showed that these four xenobiotics could stably bind to the CYP321A enzymes. Furthermore, two transcription factor genes, CncC and MafK, were significantly induced by the xenobiotics. Knockdown of CncC or MafK reduced the expression of four CYP321A genes and increased larval susceptibility to the xenobiotics. Dual-luciferase reporter assays showed that cotransfection of reporter plasmids carrying the CYP321A promoter with CncC and/or MafK-expressing constructs significantly magnified the promoter activity. These results indicate that the induction of CYP321A subfamily members conferring larval detoxification capability to xenobiotics is mediated by the activation of CncC and MafK.

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.

Root-Knot-Nematode-Encoded CEPs Increase Nitrogen Assimilation

C-terminally encoded peptides (CEPs) are plant developmental signals that regulate growth and adaptive responses to nitrogen stress conditions. These small signal peptides are common to all vascular plants, and intriguingly have been characterized in some plant parasitic nematodes. Here, we sought to discover the breadth of root-knot nematode (RKN)-encoded CEP-like peptides and define the potential roles of these signals in the plant-nematode interaction, focusing on peptide activity altering plant root phenotypes and nitrogen uptake and assimilation. A comprehensive bioinformatic screen identified 61 CEP-like sequences encoded within the genomes of six root-knot nematode (RKN; Meloidogyne spp.) species. Exogenous application of an RKN CEP-like peptide altered A. thaliana and M. truncatula root phenotypes including reduced lateral root number in M. truncatula and inhibited primary root length in A. thaliana. To define the role of RKN CEP-like peptides, we applied exogenous RKN CEP and demonstrated increases in plant nitrogen uptake through the upregulation of nitrate transporter gene expression in roots and increased 15N/14N in nematode-formed root galls. Further, we also identified enhanced nematode metabolic processes following CEP application. These results support a model of parasite-induced changes in host metabolism and inform endogenous pathways to regulate plant nitrogen assimilation.

Cytochrome P450 CYP6DB3 was involved in thiamethoxam and imidacloprid resistance in Bemisia tabaci Q (Hemiptera: Aleyrodidae)

High level resistance for a variety of insecticides has emerged in Bemisia tabaci, a globally notorious insect. Neonicotinoid insecticides have been applied widely to control B. tabaci. Whether a differentially expressed gene CYP6DB3 discovered from transcriptome data of B. tabaci is involved in the resistance to neonicotinoid insecticides remains unclear. In the study, CYP6DB3 expression was significantly up-regulated in both thiamethoxam- and imidacloprid-resistant strains relative to the susceptive strains. We also found that CYP6DB3 expression was up-regulated after B. tabaci adults were exposed to thiamethoxam and imidacloprid. Moreover, knocking down CYP6DB3 expression via feeding corresponding dsRNA significantly reduced CYP6DB3 mRNA levels by 34.1%. Silencing CYP6DB3 expression increased the sensitivity of B. tabaci Q adults against both thiamethoxam and imidacloprid. Overexpression of CYP6DB3 gene reduced the toxicity of imidacloprid and thiamethoxam to transgenic D. melanogaster. In addition, metabolic studies showed that CYP6DB3 can metabolize 24.41% imidacloprid in vitro. Collectively, these results strongly support that CYP6DB3 plays an important role in the resistance of B. tabaci Q to imidacloprid and thiamethoxam. This work will facilitate a deeper insight into the part of cytochrome P450s in the evolution of insecticide resistance and provide a theoretical basis for the development of new integrated pest resistance management.

Multiple-P450 Gene Co-Up-Regulation in the Development of Permethrin Resistance in the House Fly, Musca domestica

This paper reports a study conducted at the whole transcriptome level to characterize the P450 genes involved in the development of pyrethroid resistance, utilizing expression profile analyses of 86 cytochrome P450 genes in house fly strains with different levels of resistance to pyrethroids/permethrin. Interactions among the up-regulated P450 genes and possible regulatory factors in different autosomes were examined in house fly lines with different combinations of autosomes from a resistant house fly strain, ALHF. Eleven P450 genes that were significantly up-regulated, with levels > 2-fold those in the resistant ALHF house flies, were in CYP families 4 and 6 and located on autosomes 1, 3 and 5. The expression of these P450 genes was regulated by trans- and/or cis-acting factors, especially on autosomes 1 and 2. An in vivo functional study indicated that the up-regulated P450 genes also conferred permethrin resistance in Drosophila melanogaster transgenic lines. An in vitro functional study confirmed that the up-regulated P450 genes are able to metabolize not only cis- and trans-permethrin, but also two metabolites of permethrin, PBalc and PBald. In silico homology modeling and the molecular docking methodology further support the metabolic capacity of these P450s for permethrin and substrates. Taken together, the findings of this study highlight the important function of multi-up-regulated P450 genes in the development of insecticide resistance in house flies.

Contribution of UDP-glycosyltransferases to chlorpyrifos resistance in Nilaparvata lugens

As a multigene superfamily of Phase II detoxification enzymes, uridine diphosphate (UDP)-glycosyltransferases (UGTs) play important roles in the metabolism of xenobiotics including insecticides. In this study, 5-nitrouracil, an inhibitor of UGT enzyme activity, effectively increased the toxicity of chlorpyrifos to the chlorpyrifos-resistant strain of Nilaparvata lugens, one of the most resistant rice pests. The enzyme content of UGT in the resistant strain was significantly higher than that in the susceptible strain. Among 20 identified UGT genes, UGT386H2, UGT386J2, UGT386N2 and UGT386P1 were found significantly overexpressed in the resistant strain and can be effectively induced by chlorpyrifos. These four UGT genes were most highly expressed in the midgut and/or fat body, two main insect detoxification tissues. Amino acid sequence alignments revealed that these four UGTs contained a variable N-terminal substrate-binding domain and a conserved C-terminal sugar donor-binding domain. Furthermore, homology modeling and molecular docking analyses showed that these UGTs could stably bind to chlorpyrifos and chlorpyrifos oxon, with the binding free energies from -19.4 to -110.62 kcal mol^-1. Knockdown of UGT386H2 or UGT386P1 by RNA interference dramatically increased the susceptibility of the resistant strain to chlorpyrifos. These findings suggest that overexpression of these two UGT genes contributes to chlorpyrifos resistance in N. lugens.

Disruption of CYP6DF1 and CYP6DJ2 increases the susceptibility of Dendroctonus armandi to (+)-α-pinene

Bark beetles rely on detoxifying enzymes to resist the defensive oleoresin terpenes of the host tree. Insect cytochrome P450 (CYPs) plays a key role in the detoxification of plant allelochemicals and pesticides. CYP6 family is unique to Insecta, and its biochemical function is basically related to catabolize heterologous substances. In this study, two Dendroctonus armandi CYP6 genes, CYP6DF1 and CYP6DJ2, were characterized. Spatiotemporal expression profiling revealed that CYP6DF1 and CYP6DJ2 expressions were higher in larvae and adult stages of D. armandi than in egg and pupae stages, and that two genes predominantly expressed in brain, midgut, fat body, or Malpighian tubules. Moreover, CYP6DF1 and CYP6DJ2 expressions were significantly induced after exposure to (+)-α-pinene. Importantly, silencing CYP6DF1 and CYP6DJ2 significantly inhibited the CYP activity and increased the mortality in the adults fumigated with (+)-α-pinene. Additionally, piperonyl butoxide exposure to adults also increase the sensitivity after treatment with (+)-α-pinene, which led to a significant reduction of the CYP activity, resulting a significant increase in adult mortality. These results suggest that the CYP6 family plays a key role in determining the susceptibility of D. armandi to (+)-α-pinene, which may have implications for the development of novel therapeutics to control this important pest.