Regulation of insect P450s in response to phytochemicals

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.

A relaxin receptor gene RpGPCR41 is involved in the resistance of Rhopalosiphum padi to pyrethroids

Rhopalosiphum padi is a global pest that poses a significant threat to wheat crops and has developed resistance to various insecticides. G protein-coupled receptors (GPCRs), known for their crucial role in signaling and biological processes across insect species, have recently gained attention as a potential target for insecticides. GPCR has the potential to contribute to insect resistance through the regulation of P450 gene expression. However, GPCRs in R. padi remained unexplored until this study. We identified a total of 102 GPCRs in R. padi, including 81 receptors from family A, 10 receptors from family B, 8 receptors from family C, and 3 receptors from family D. Among these GPCR genes, 16 were up-regulated in both lambda-cyhalothrin and bifenthrin-resistant strains of R. padi (LC-R and BIF-R). A relaxin receptor gene, RpGPCR41, showed the highest up-regulated expression in both the resistant strains, with a significant increase of 14.3-fold and 22.7-fold compared to the susceptible strain (SS). RNA interference (RNAi) experiments targeting the relaxin receptor significantly increase the mortality of R. padi when exposed to the LC50 concentration of lambda-cyhalothrin and bifenthrin. The expression levels of five P450 genes (RpCYP6CY8, RpCYP6DC1, RpCYP380B1, RpCYP4CH2, and RpCYP4C1) were significantly down-regulated following knockdown of RpGPCR41 in LC-R and BIF-R strains. Our results highlight the involvement of GPCR gene overexpression in the resistance of R. padi to pyrethroids, providing valuable insights into the mechanisms underlying aphid resistance and a potential target for aphid control.

Secondary metabolites in host pears defense against two fruit borers and cytochrome-P450-mediated counter-defense

Herbivorous insects have evolved metabolic strategies to survive the challenges posed by plant secondary metabolites (SMs). This study reports an exploration of SMs present in pears, which serve as a defense against invasive Cydia pomonella and native Grapholita molesta and their counter-defense response. The feeding preferences of fruit borers are influenced by the softening of two pear varieties as they ripen. The content of SMs, such as quercetin and rutin, increases due to feeding by fruit borers. Notably, quercetin levels only increase after C. pomonella feeding. The consumption of SMs affects the growth of fruit borer population differently, potentially due to the activation of P450 genes by SMs. These two fruit borers are equipped with specific P450 enzymes that specialize in metabolizing quercetin and rutin, enabling them to adapt to these SMs in their host fruits. These findings provide valuable insights into the coevolution of plants and herbivorous insects.

Oral administration of phytochemicals protects honey bees against cognitive and motor impairments induced by the insecticide fipronil

Pollution produced by exposure to pesticides is a major concern for food security because the negative impacts on pollinators. Fipronil, an insecticide broadly used around the globe has been associated with the ongoing decline of bees. With a characteristic neuroactive toxicodynamic, fipronil leads to cognitive and motor impairments at sublethal dosages. Despite of regional bans, multilevel strategies are necessary for the protection of pollinators. Recent evidence suggests that specific nutrients in the diets of bees may induce protection against insecticides. Here, we evaluated whether the administration of three phytochemicals, namely rutin, kaempferol and p-coumaric acid provide protection to the Africanized honey bee Apis mellifera against oral administration of realistic dosages of fipronil. We tested the potential impairment produced by fipronil and the protection induced by the phytochemicals in learning, 24h memory, sucrose sensitivity and motor control. We found that the administration of fipronil induced a concentration-dependent impairment in learning and motor control, but not 24h memory or sucrose sensitivity across a 24h window. We also found that the administration of rutin, p-coumaric acid, kaempferol and the mixture was innocuous and generally offered protection against the impairments induced by fipronil. Overall, our results indicate that bees can be prophylactically protected against insecticides via nutrition, providing an alternative to the ongoing conflict between the use of insecticides and the decline of pollinators. As the studied phytochemicals are broadly present in nectar and pollen, our results suggest that the nutritional composition, and not only its production, should be considered when implementing strategies of conservation via gardens and co-cropping.

Characterization and functional analysis of UDP-glycosyltransferases reveal their contribution to phytochemical flavone tolerance in Spodoptera litura

Efficient detoxification is the key factor for phytophagous insect to adapt to phytochemicals. However, the role of uridine diphosphate (UDP)-glycosyltransferases (UGTs) in insect anti-defense to phytochemical flavone is largely unknown. In this study, 52 UGT genes were identified in Spodoptera litura and they presented evident gene duplication. UGT played a crucial part in larval tolerance to flavone because the enzyme activity and transcriptional level of 77 % UGT members were remarkably upregulated by flavone administration and suppression of UGT enzyme activity and gene expressions significantly increased larval susceptibility to flavone. Bacteria coexpressing UGTs had high survival rates under flavone treatment and flavone was dramatically metabolized by UGT recombinant cells, which indicated the involvement of UGTs in flavone detoxification. What's more, ecdysone pathway was activated by flavone. Topical application of 20-hydroxyecdysone highly upregulated UGT enzyme activity and more than half of UGT expressions. The effects were opposite when ecdysone receptor (EcR) and ultraspiracle (USP)-mediated ecdysone signaling pathway was inhibited. Furtherly, promoter reporter assays of 5 UGT genes showed that their transcription activities were notably increased by cotransfection with EcR and USP. In consequence, this study suggested that UGTs were involved in flavone detoxification and their transcriptional expressions were regulated by ecdysone pathway.

Up-regulation of CYP6G4 mediated by a CncC/maf binding-site-containing insertion confers resistance to multiple classes of insecticides in the house fly Musca domestica

Populations of many insect species have evolved a variety of resistance mechanisms in response to insecticide selection. Current knowledge about mutations responsible for insecticide resistance is largely achieved from studies on target-site resistance, while much less is known about metabolic resistance. Although it is well known that P450 monooxygenases are one of the major players involved in insecticide metabolism and resistance, understanding mutation(s) responsible for CYP-mediated resistance has been a big challenge. In this study, we used the house fly to pursue a better understanding of P450 mediated insecticide resistance at the molecular level. Metabolism studies illustrated that CYP6G4 had a broad-spectrum metabolic activity in metabolizing insecticides. Population genotyping revealed that the CYP6G4v1 allele harboring a DNA insertion (MdIS1) had been selected in many house fly populations on different continents. Dual luciferase reporter assays identified that the MdIS1 contained a CncC/Maf binding site, and electrophoretic mobility shift assay confirmed that transcription factor CncC was involved in the MdIS1-mediated regulation. This study highlights the common involvement of the CncC pathway in adaptive evolution, and provides an interesting case supportive of parallel evolution in P450-mediated insecticide resistance in insects.

RNA interference of NADPH-cytochrome P450 reductase increases the susceptibility of Aphis gossypii Glover to sulfoxaflor

NADPH-cytochrome P450 reductase (CPR) is essential for the detoxification of endogenous and exogenous substances mediated by cytochrome P450. While several insect CPRs have been found to be associated with insecticide resistance, the CPR of Aphis gossypii has not been characterized, and its functional role in insecticide resistance remains undefined. In this study, we cloned and characterized the full-length sequence of A. gossypii CPR (AgCPR). The deduced amino acid sequence of AgCPR contains all conserved domains of CPR, which shows high similarity to other insect CPRs and was clustered into a same branch of aphids according to phylogenetic analysis. The transcript of AgCPR was present in all developmental stages, with the highest expression in the adult stage. Furthermore, the expression of AgCPR could be induced by sulfoxaflor, a commonly used insecticide, in a time- and dose-dependent manner. Further silencing of AgCPR by feeding dsRNA significantly increased the susceptibility of A. gossypii to this insecticide. These findings suggest that AgCPR may play a significant role in the susceptibility of A. gossypii to sulfoxaflor and in the development of P450-mediated resistance to sulfoxaflor.

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.

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.

Transcriptome and gut microbiota analyses reveal a possible mechanism underlying rifampin-mediated interruption of the larval development of chironomid Propsilocerus akamusi (Diptera: Chironomidae)

Chironomids, the most abundant insect group found in freshwater habitats, are known to be pollution tolerate and serve as important bioindicators of contaminant stress. Gut microbiota has recently been shown to potentially provide a number of beneficial services to insect hosts. However, the antibiotic-mediated interruption of chironomid gut microbial community and its subsequent influence on host body are still unclear. In the present study, the effects of rifampin on chironomid larvae were investigated at both transcriptome and microbiome level to assess the relationship between gut bacteria and associated genes. Our data indicated that the rifampin-induced imbalance of gut ecosystem could inhibit the development of chironomid larvae via decreasing the body weight, body length and larval eclosion rate during 96-h treatment. Both the community structure and taxonomic composition were significantly altered due to the invasion of rifampin in digestive tracts. The relative abundance of phylum Deferribacterota and Bacteroidota were dramatically increased with rifampin exposure. A set of genes involved in amino acid synthesis as well as xenobiotic metabolism pathways were greatly changed and proved to have tight correlation with certain genus. Bacterial genus Tyzzerella was positively correlated with detoxifying PaCYP6GF1 and PaCYP9HL1 genes. This study provides a reference for understanding the environmental risks of antibiotic and aims to accelerate new biological insights into the effects of antibiotic on the fitness of chironomids and into the microbe mediated-regulatory mechanism of aquatic insects.

Enthralling genetic regulatory mechanisms meddling insecticide resistance development in insects: role of transcriptional and post-transcriptional events

Insecticide resistance in insects severely threatens both human health and agriculture, making insecticides less compelling and valuable, leading to frequent pest management failures, rising input costs, lowering crop yields, and disastrous public health. Insecticide resistance results from multiple factors, mainly indiscriminate insecticide usage and mounted selection pressure on insect populations. Insects respond to insecticide stress at the cellular level by modest yet significant genetic propagations. Transcriptional, co-transcriptional, and post-transcriptional regulatory signals of cells in organisms regulate the intricate processes in gene expressions churning the genetic information in transcriptional units into proteins and non-coding transcripts. Upregulation of detoxification enzymes, notably cytochrome P450s (CYPs), glutathione S-transferases (GSTs), esterases [carboxyl choline esterase (CCE), carboxyl esterase (CarE)] and ATP Binding Cassettes (ABC) at the transcriptional level, modification of target sites, decreased penetration, or higher excretion of insecticides are the noted insect physiological responses. The transcriptional regulatory pathways such as AhR/ARNT, Nuclear receptors, CncC/Keap1, MAPK/CREB, and GPCR/cAMP/PKA were found to regulate the detoxification genes at the transcriptional level. Post-transcriptional changes of non-coding RNAs (ncRNAs) such as microRNAs (miRNA), long non-coding RNAs (lncRNA), and epitranscriptomics, including RNA methylation, are reported in resistant insects. Additionally, genetic modifications such as mutations in the target sites and copy number variations (CNV) are also influencing insecticide resistance. Therefore, these cellular intricacies may decrease insecticide sensitivity, altering the concentrations or activities of proteins involved in insecticide interactions or detoxification. The cellular episodes at the transcriptional and post-transcriptional levels pertinent to insecticide resistance responses in insects are extensively covered in this review. An overview of molecular mechanisms underlying these biological rhythms allows for developing alternative pest control methods to focus on insect vulnerabilities, employing reverse genetics approaches like RNA interference (RNAi) technology to silence particular resistance-related genes for sustained insect management.

A detoxification pathway initiated by a nuclear receptor TcHR96h in Tetranychus cinnabarinus (Boisduval)

Understanding the mechanism of detoxification initiation in arthropods after pesticide exposure is crucial. Although the identity of transcription factors that induce and regulate the expression of detoxification genes in response to pesticides is beginning to emerge, whether transcription factors directly interact with xenobiotics is unclear. The findings of this study revealed that a nuclear hormone receptor, Tetranychus cinnabarinus hormone receptor (HR) TcHR96h, regulates the overexpression of the detoxification gene TcGSTm02, which is involved in cyflumetofen resistance. The nuclear translocation of TcHR96h increased after cyflumetofen exposure, suggesting direct binding with cyflumetofen. The direct binding of TcHR96h and cyflumetofen was supported by several independent proteomic assays that quantify interactions with small molecules. Together, this study proposes a model for the initiation of xenobiotic detoxification in a polyphagous agricultural pest. These insights not only provide a better understanding of the mechanisms of xenobiotic detoxification and metabolism in arthropods, but also are crucial in understanding adaptation in polyphagous herbivores.

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

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

CYP6CX2 and CYP6CX3 mediate thiamethoxam resistance in field whitefly, Bemisia tabaci (Hemiptera:Aleyrodidae)

Cytochrome P450 monooxygenases (P450s) are well-known for their crucial roles in the detoxification of xenobiotics. However, whether CYP6CX2 and CYP6CX3, 2 genes from our Bemisia tabaci (B. tabaci) MED/Q genome data were associated with detoxification metabolism and confer resistance to thiamethoxam is unclear. In this study, we investigated the role of CYP6CX2 and CYP6CX3 in mediating whitefly thiamethoxam resistance. Our results showed that mRNA levels of CYP6CX2 and CYP6CX3 were up-regulated after exposure to thiamethoxam. Transcriptional levels of 2 genes were overexpressed in laboratory and field thiamethoxam resistant strains by RT-qPCR. These results indicate that the enhanced expression of CYP6CX2 and CYP6CX3 appears to confer thiamethoxam resistance in B. tabaci. Moreover, linear regression analysis showed that the expression levels of CYP6CX2 and CYP6CX3 were positively correlated with thiamethoxam resistance levels among populations. The susceptibility of whitefly adults was markedly increased after silencing 2 genes by RNA interference (RNAi) which further confirming their major role in thiamethoxam resistance. Our findings provide information to better understand the roles of P450s in resistance to neonicotinoids and suggest that these genes may be applied to develop target genes for sustainable management tactic of agricultural pests such as B. tabaci.

Identification of the Flavone-Inducible Counter-Defense Genes and Their cis-Elements in Helicoverpa armigera

Flavone is widely found in plants and plays an important role in plant defense against pests. Many pests, such as Helicoverpa armigera, use flavone as a cue to upregulate counter-defense genes for detoxification of flavone. Yet the spectrum of the flavone-inducible genes and their linked cis-regulatory elements remains unclear. In this study, 48 differentially expressed genes (DEGs) were found by RNA-seq. These DEGs were mainly concentrated in the retinol metabolism and drug metabolism-cytochrome P450 pathways. Further in silico analysis of the promoter regions of 24 upregulated genes predicted two motifs through MEME and five previously characterized cis-elements including CRE, TRE, EcRE, XRE-AhR and ARE. Functional analysis of the two predicted motifs and two different versions of ARE (named ARE1 and ARE2) in the promoter region of the flavone-inducible carboxylesterase gene CCE001j verified that the two motifs and ARE2 are not responsible for flavone induction of H. armigera counter-defense genes, whereas ARE1 is a new xenobiotic response element to flavone (XRE-Fla) and plays a decisive role in flavone induction of CCE001j. This study is of great significance for further understanding the antagonistic interaction between plants and herbivorous insects.

Nuclear receptors potentially regulate phytochemical detoxification in Spodoptera litura

Phytochemicals are a class of potential pesticides for pest control. Our previous studies have demonstrated that the development of Spodoptera litura is suppressed by two phytochemicals, flavone and xanthotoxin. Generally, phytochemical is metabolized by insect detoxification enzyme systems. Nuclear receptor (NR) is the ligand-activated transcription factor that involved in the regulation of detoxification gene expressions. To explore how NR responds to phytochemical to mediate detoxification gene expression, in the present study, 19 NRs were firstly identified in S. litura genome. The transcriptional levels of most NRs were significantly induced in the midgut of S. litura larvae after exposure to flavone and xanthotoxin. RNAi-mediated knockdown of FTZF1, EcR, Dsf, and HR3 remarkably reduced the larval tolerance to flavone or xanthotoxin. In addition, many crucial detoxification genes were downregulated by dsNR administrations, which might be responsible for the high sensitivity of S. litura to phytochemicals. Molecular docking indicated that phytochemicals as the potential ligands had high affinity to bind to NRs. This study suggested that NR potentially regulated the transcriptional expression of detoxification genes in response to phytochemical stresses, which partially elucidated the mechanism of extensive host adaptation in S. litura and provided the theoretical evidences for the development of NR-targeted insecticides.

Transcription factor CncC potentially regulates cytochrome P450 CYP321A1-mediated flavone tolerance in Helicoverpa armigera

Insect P450s play crucial roles in metabolizing insecticides and toxic plant allelochemicals. In this study, our results demonstrate that Helicoverpa armigera can adapt to a lower concentration of flavone (a flavonoid phytochemical), and P450 activities and CYP321A1 transcript levels significantly increase after exposure to flavone. RNAi-mediated knockdown of CYP321A1 significantly reduced the tolerance of H. armigera larvae to flavone. In addition, the regulatory mechanisms driving CYP321A1 induction following exposure to flavone were investigated. Flavone exposure significantly increased H₂O₂ generation in the larval midgut. The mRNA levels of HaCncC and HaMaf-s significantly increased in the midgut of H. armigera after exposure to flavone. Knockdown of HaCncC significantly inhibited expression of flavone-induced CYP321A1 and resulted in a decrease in flavone induction of CYP321A1. HaCncC knockdown significantly reduced the tolerance of H. armigera larvae to flavone. Taken together, these results indicate that HaCncC regulates expression of the CYP321A1 gene responsible for flavone tolerance in H. armigera.

Activation of the CncC pathway is involved in the regulation of P450 genes responsible for clothianidin resistance in Bradysia odoriphaga

BACKGROUND

Insect cytochrome P450 monooxygenases (P450s) play a key role in the detoxification metabolism of insecticides and their overexpression is often associated with insecticide resistance. Our previous research showed that the overexpression of four P450 genes is responsible for clothianidin resistance in B. odoriphaga. In this study, we characterized another P450 gene, CYP6FV21, associated with clothianidin resistance. However, the molecular basis for the overexpression of P450 genes in clothianidin-resistant strain remains obscure in B. odoriphaga.

RESULTS

In this study, the CYP6FV21 gene was significantly overexpressed in the clothianidin-resistant (CL-R) strain. Clothianidin exposure significantly increased the expression level of CYP6FV21. Knockdown of CYP6FV21 significantly increased the susceptibility of B. odoriphaga larvae to clothianidin. The transcription factor Cap 'n' Collar isoform-C (CncC) was highly expressed in the midgut of larvae in B. odoriphaga. The expression level of CncC was higher in the CL-R strain compared with the susceptible (SS) strain. Clothianidin exposure caused reactive oxygen species (ROS) accumulation and significantly increased the expression level of CncC. Knockdown of CncC caused a significant decrease in the expression of CYP3828A1 and CYP6FV21, and P450 enzyme activity, and led to a significant increase in mortality after exposure to lethal concentration at 30% (LC₃₀ ) of clothianidin. After treatment with CncC agonist curcumin, the P450 activity and the expression levels of CYP3828A1 and CYP6FV21 significantly increased, and larval sensitivity to clothianidin decreased. The ROS scavenger N-acetylcysteine (NAC) treatment significantly inhibited the expression levels of CncC, CYP3828A1 and CYP6FV21 in response to clothianidin exposure and increased larval sensitivity to clothianidin.

CONCLUSION

Taken together, these results indicate that activation of the CncC pathway by the ROS burst plays a critical role in clothianidin resistance by regulating the expression of CYP3828A1 and CYP6FV21 genes in B. odoriphaga. This study provides more insight into the mechanisms underlying B. odoriphaga larval resistance to clothianidin. © 2023 Society of Chemical Industry.

Transcriptomic Analysis Reveals the Detoxification Mechanism of Chilo suppressalis in Response to the Novel Pesticide Cyproflanilide

Chilo suppressalis is one of the most damaging rice pests in China’s rice-growing regions. Chemical pesticides are the primary method for pest control; the excessive use of insecticides has resulted in pesticide resistance. C. suppressalis is highly susceptible to cyproflanilide, a novel pesticide with high efficacy. However, the acute toxicity and detoxification mechanisms remain unclear. We carried out a bioassay experiment with C. suppressalis larvae and found that the LD10, LD30 and LD50 of cyproflanilide for 3rd instar larvae was 1.7 ng/per larvae, 6.62 ng/per larvae and 16.92 ng/per larvae, respectively. Moreover, our field trial results showed that cyproflanilide had a 91.24% control efficiency against C. suppressalis. We investigated the effect of cyproflanilide (LD30) treatment on the transcriptome profiles of C. suppressalis larvae and found that 483 genes were up-regulated and 305 genes were down-regulated in response to cyproflanilide exposure, with significantly higher CYP4G90 and CYP4AU10 expression in the treatment group. The RNA interference knockdown of CYP4G90 and CYP4AU10 increased mortality by 20% and 18%, respectively, compared to the control. Our results indicate that cyproflanilide has effective insecticidal toxicological activity, and that the CYP4G90 and CYP4AU10 genes are involved in detoxification metabolism. These findings provide an insight into the toxicological basis of cyproflanilide and the means to develop efficient resistance management tools for C. suppressalis.

The variation of a cytochrome P450 gene, CYP6G4, drives the evolution of Musca domestica L. (Diptera: Muscidae) resistance to insecticides in China

Long term and excessive insecticide use has resulted in some environmental problems and especially, insecticide resistance evolution in insect pests. The variation of cytochrome P450 monooxygenases (P450s), associated with the metabolic detoxification of toxic xenobiotics, is often involved in insecticide resistance. Here, we found that the variation in a P450 gene, CYP6G4, is the most important driver of carbamates resistance in the house fly (Musca domestica). Deciphering the detailed molecular mechanisms of the insecticide resistance is critical for performing suitable insecticide resistance management strategies. Our research results revealed that the combination of amino acid mutations (110C-330E-360N/S, 110C-330E-360S) of CYP6G4 could improve the resistance to propoxur. The nucleotide variations in the promoter region of CYP6G4 significantly increased the luciferase activity by the reporter gene assays. Additionally, miR-281-1-5p was confirmed to post-transcriptionally down-regulate the expression of CYP6G4. These findings suggest that three independent mechanisms; amino acid mutations of the P450 protein, mutations in the promoter region and low expression of post-trans-regulatory factors, as the powerful strategies for the insect resistance to toxic compounds, play a crucial role in the evolutionary processes of insecticide resistance.

Cap 'n' Collar C and Aryl Hydrocarbon Receptor Nuclear Translocator Facilitate the Expression of Glutathione S-Transferases Conferring Adaptation to Tannic Acid and Quercetin in Micromelalopha troglodyta (Graeser) (Lepidoptera: Notodontidae)

Micromelalopha troglodyta (Graeser) (Lepidoptera: Notodontidae) is a notorious pest of poplar. Coevolution with poplars rich in plant secondary metabolites prompts M. troglodyta to expand effective detoxification mechanisms against toxic plant secondary metabolites. Although glutathione S-transferases (GSTs) play an important role in xenobiotic detoxification in M. troglodyta, it is unclear how GSTs act in response to toxic secondary metabolites in poplar. In this study, five GST gene core promoters were accurately identified by a 5' loss luciferase reporter assay, and the core promoters were significantly induced by two plant secondary metabolites in vitro. Two transcription factors, cap 'n' collar C (CncC) and aryl hydrocarbon receptor nuclear translocator (ARNT), were cloned in M. troglodyta. MtCncC and MtARNT clustered well with other insect CncCs and ARNTs, respectively. In addition, MtCncC and MtARNT could bind the MtGSTt1 promoter and strongly improve transcriptional activity, respectively. However, MtCncC and MtARNT had no regulatory function on the MtGSTz1 promoter. Our findings revealed the molecular mechanisms of the transcription factors MtCncC and MtARNT in regulating the GST genes of M. troglodyta. These results provide useful information for the control of M. troglodyta.

A transposon-introduced G-quadruplex motif is selectively retained and constrained to downregulate CYP321A1

Insects utilize xenobiotic compounds to up- and downregulate cytochrome P450 monooxygenases (P450s) involved in detoxification of toxic xenobiotics including phytochemicals and pesticides. G-quadruplexes (G4)-forming DNA motifs are enriched in the promoter regions of transcription factors and function as cis-acting elements to regulate these genes. Whether and how P450s gain and keep G4 DNA motifs to regulate their expression still remain unexplored. Here, we show that CYP321A1, a xenobiotic-metabolizing P450 from Helicoverpa zea, a polyphagous insect of economic importance, has acquired and preserved a G4 DNA motif by selectively retaining a transposon known as HzIS1-3 that carries this G4 DNA motif in its promoter region. The HzIS1-3 G4 DNA motif acts as a silencer to suppress the constitutive and induced expression of CYP321A1 by plant allelochemicals flavone and xanthotoxin through folding into an intramolecular parallel or hybrid-1 conformation in the absence or presence of K⁺ . The G4 ligand N-methylmesoporphyrin IX (NMM) strengthens the silencing effect of HzIS1-3 G4 DNA motif by switching its structure from hybrid-1 to hybrid-2. The enrichment of transposons in P450s and other environment-adaptation genes implies that selective retention of G4 DNA motif-carrying transposons may be the main evolutionary route for these genes to obtain G4 DNA motifs.

Genome-wide and expression-profiling analyses of the cytochrome P450 genes in Tenebrionidea

Cytochrome P450 monooxygenases (CYPs) are present in almost all areas of the tree of life. As one of the largest and most diverse superfamilies of multifunctional enzymes, they play important roles in the metabolism of xenobiotics and biosynthesis of endogenous compounds, shaping the success of insects. In this study, the CYPome (an omics term for all the CYP genes in a genome) diversification was examined in the four Tenebrionidea species through genome-wide analysis. A total of 483 CYP genes were identified, of which 103, 157, 122, and 101 were respectively deciphered from the genomes of Tebebrio molitor, Asbolus verucosus, Hycleus cichorii and Hycleus phaleratus. These CYPs were classified into four major clans (mitochondrial, CYP2, CYP3, and CYP4), and clans CYP3 and CYP4 are most diverse. Phylogenetic analysis showed that most CYPs of these Tenebrionidea beetles from each clan had a very close 1:1 orthology to each other, suggesting that they originate closely and have evolutionally conserved function. Expression analysis at different developmental stages and in various tissues showed the life stage-, gut-, salivary gland-, fat body-, Malpighian tubule-, antennae-, ovary- and testis-specific expression patterns of T. molitor CYP genes, implying their various potential roles in development, detoxification, immune response, digestion, olfaction, and reproduction. Our studies provide a platform to understand the evolution of Tenebrionidea CYP gene superfamily, and a basis for further functional investigation of the T. molitor CYPs involved in various biological processes.

Activation of the ROS/CncC Signaling Pathway Regulates Cytochrome P450 CYP4BQ1 Responsible for (+)-α-Pinene Tolerance in Dendroctonus armandi

Bark beetles mainly rely on detoxification enzymes to resist the host tree's defense against oleoresin terpenes. Cytochrome P450 enzymes (CYPs) play an important role in the detoxification of plant allelochemicals and pesticides in insect. One P450 gene (DaCYP4BQ1) is associated with the response of (+)-α-pinene in Dendroctonus armandi. However, the regulatory mechanism of this P450 gene response to (+)-α-pinene is still unknown. In this study, spatiotemporal expression profiling indicated that CYP4BQ1 was highly expressed in adult and larval stages of D. armandi, and it was predominantly expressed in fat body, midgut, and Malpighian tubules of adults. Moreover, the expression of CYP4BQ1 significantly increased after exposure to (+)-α-pinene, and depletion of it decreased the tolerance of adults to (+)-α-pinene. In addition, (+)-α-pinene treatment induced the expression of the transcription factors cap 'n' collar isoform C (CncC) and its binding factor muscle aponeurosis fibromatosis (Maf), elevated the level of hydrogen peroxide (H₂O₂), and increased the activities of antioxidant enzymes. Silencing CncC suppressed CYP4BQ1 expression and enhanced the susceptibility of beetles to (+)-α-pinene. Similarly, application of the reactive oxygen species (ROS) scavenger N-acetylcysteine reduced the production and accumulation of H₂O₂, suppressed the expression of CncC, Maf, and CYP4BQ1 and led to decreased tolerance of adults to (+)-α-pinene. In contrast, ingestion of the CncC agonist curcumin elevated CYP4BQ1 expression and enhanced (+)-α-pinene tolerance. The results demonstrate that, in D. armandi, (+)-α-pinene induces CYP4BQ1 via activation of the ROS/CncC signaling pathway.

Three cytochrome P450 CYP4 family genes regulated by the CncC signaling pathway mediate phytochemical susceptibility in the red flour beetle, Tribolium castaneum

BACKGROUND

Insect cytochrome P450 monooxygenases (P450s) play a crucial role in phytochemical metabolism and tolerance. Three P450 genes (TcCYP4Q3, TcCYP4Q5, and TcCYP4Q7) are associated with the response of eugenol in Tribolium castaneum. However, the responding mechanisms of these P450 genes to eugenol remain unknown.

RESULTS

Here, spatiotemporal expression profiling revealed that TcCYP4Q3 and TcCYP4Q5 were most highly expressed in late adult, while TcCYP4Q7 was predominantly expressed in late larva; and all of these three P450 genes were mainly expressed in the fat body of larvae. Furthermore, the expressions of these three P450 genes were significantly up-regulated after exposure to eugenol, and depletion of them enhanced the susceptibility of beetles to eugenol. Interestingly, RNA interference (RNAi) against the CncC gene, a transcription factor of CncC signaling pathway associated with regulation of insect P450s in response to phytochemicals, reduced the transcripts of these three P450 genes following exposure to eugenol. Investigation of CncC signaling pathway showed that this pathway could be activated by eugenol.

CONCLUSION

Altogether, the results indicate that these three P450 genes are regulated by CncC signaling pathway to participate in the susceptibility of Tribolium castaneum to phytochemicals. These findings will aid implications for the development of novel therapeutics to control pest. © 2022 Society of Chemical Industry.

Imidacloprid-induced pathophysiological damage in the midgut of Locusta migratoria (Orthoptera: Acrididae) in the field

Neonicotinoids are modern insecticides widely used in agriculture worldwide. Their impact on target (nervous system) and non-target (midgut) tissues has been well studied in beneficial insects including honeybees under controlled conditions. However, their detailed effects on pest insects on the field are missing to date. Here, we have studied the effects of the neonicotinoid imidacloprid on the midgut of the pest insect Locusta migratoria caught in the field. We found that in the midgut of imidacloprid-exposed locusts the activity of enzymes involved in reactive oxygen metabolism was perturbed. By contrast, the activity of P450 enzymes that have been shown to be activated in a detoxification response and that were also reported to produce reactive oxygen species was elevated. Probably as a consequence, markers of oxidative stress including protein carbonylation and lipid peroxidation accumulated in midgut samples of these locusts. Histological analyses revealed that their midgut epithelium is disorganized and that the brush border of the epithelial cells is markedly reduced. Indeed, microvilli are significantly shorter, misshapen and possibly non-functional in imidacloprid-treated locusts. We hypothesize that imidacloprid induces oxidative stress in the locust midgut, thereby changing the shape of midgut epithelial cells and probably in turn compromising their physiological function. Presumably, these effects reduce the survival rate of imidacloprid-treated locusts and the damage they cause in the field.

Functional investigation of lncRNAs and target cytochrome P450 genes related to spirotetramat resistance in Aphis gossypii Glover

BACKGROUND

Spirotetramat is a tetramic acid derivative insecticide with novel modes of action for controlling Aphis gossypii Glover in the field. Previous studies have shown that long noncoding RNAs (lncRNAs) and cytochrome P450 monooxygenases (P450s) are involved in the detoxification process. However, the functions of lncRNAs in regulating P450 gene expression in spirotetramat resistance in A. gossypii are unknown.

RESULTS

In this study, we found CYP4CJ1, CYP6CY7 and CYP6CY21 expression levels to be significantly upregulated in a spirotetramat-resistant (SR) strain compared with a susceptible (SS) strain. Furthermore, knockdown of CYP4CJ1, CYP6CY7 and CYP6CY21 increased nymph and adult mortality in the SR strain following exposure to spirotetramat. Drosophila ectopically expressing CYP380C6, CYP4CJ1, CYP6DA2, CYP6CY7 and CYP6CY21 showed significantly decreased mortality after spirotetramat exposure, and CYP380C6, CYP4CJ1 and CYP6CY21 are putative targets of six lncRNAs. Silencing of lncRNAs MSTRG.36649.2/5 and MSTRG.71880.1 changed CYP6CY21 and CYP380C6 expression, altering the sensitivity of the SR strain to spirotetramat. Moreover, MSTRG.36649.2/5 did not compete for microRNA (miRNA) binding to regulate CYP6CY21 expression.

CONCLUSION

Our results confirm that CYP380C6, CYP4CJ1, CYP6DA2, CYP6CY7 and CYP6CY21 are potentially involved in the development of spirotetramat resistance in A. gossypii, and MSTRG.36649.2/5 and MSTRG.71880.1 probably regulate CYP6CY21 and CYP380C6 expression other than through the "sponge effect" of competing for miRNA binding. Our results provide a favorable molecular basis for studying cotton aphid P450 genes and lncRNA functions in spirotetramat resistance development.

Activation of the ROS/CncC and 20-Hydroxyecdysone Signaling Pathways Is Associated with Xanthotoxin-Induced Tolerance to λ-Cyhalothrin in Spodoptera litura

Adaptation to phytochemicals in herbivorous insects can influence tolerance to insecticides. However, it is unclear how insects use phytochemicals as cues to activate their metabolic detoxification systems. In this study, we found that dietary exposure to xanthotoxin enhanced tolerance of Spodoptera litura larvae to λ-cyhalothrin. Xanthotoxin ingestion significantly elevated the mRNA levels of 35 detoxification genes as well as the transcription factors Cap 'n' collar isoform-C (CncC) and its binding factor small muscle aponeurosis fibromatosis isoform-K (MafK). Additionally, xanthotoxin exposure increased the levels of reactive oxygen species (ROS), while ROS inhibitor N-acetylcysteine (NAC) treatment blocked xanthotoxin-induced expression of CncC, MafK, and detoxification genes and also prevented xanthotoxin-enhanced larval tolerance to λ-cyhalothrin. The 20-hydroxyecdysone (20E) signaling pathway was effectively activated by xanthotoxin, while blocking of 20E signaling transduction prevented xanthotoxin-enhanced larval tolerance to λ-cyhalothrin. Application of 20E induced the expression of multiple xanthotoxin-induced detoxification genes and enhanced λ-cyhalothrin tolerance in S. litura. NAC treatment blocked xanthotoxin-induced 20E synthesis, while the CncC agonist curcumin activated the 20E signaling pathway. These results indicate that the ROS/CncC pathway controls the induction of metabolic detoxification upon exposure to xanthotoxin, at least in part, through its regulation of the 20E signaling pathway.

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.

Phytochemical Flavone Confers Broad-Spectrum Tolerance to Insecticides in Spodoptera litura by Activating ROS/CncC-Mediated Xenobiotic Detoxification Pathways

Tolerance to chemical insecticides can be driven by the necessity of herbivorous insects to defend against host plant-produced phytochemicals. However, how the phytochemicals are sensed and further transduced into a defense response associated with insecticide tolerance is poorly understood. Herein, we show that pre-exposure to flavone, a flavonoid phytochemical, effectively enhanced larval tolerance to multiple synthetic insecticides and elevated detoxification enzyme activities in Spodoptera litura. RNA-Seq analysis revealed that flavone induced a spectrum of genes spanning phase I and II detoxification enzyme families, as well as two transcription factors Cap "n" collar isoform C (CncC) and its partner small muscle aponeurosis fibromatosis (MafK). Knocking down of CncC by RNA interference suppressed flavone-induced detoxification gene expression and rendered the larvae more sensitive to the insecticides. Flavone exposure elicited a reactive oxygen species (ROS) burst, while scavenging of ROS inhibited CncC-mediated detoxification gene expression and suppressed flavone-induced detoxification enzyme activation. Metabolome analysis showed that the ingested flavone was mainly converted into three flavonoid metabolites, and only 3-hydroxyflavone was found to affect the ROS/CncC pathway-mediated metabolic detoxification. These results indicate that the ROS/CncC pathway is an important route driving detoxification gene expression responsible for insecticide tolerance after exposure to the phytochemical flavone.

Peroxiredoxin alleviates the fitness costs of imidacloprid resistance in an insect pest of rice

Chemical insecticides have been heavily employed as the most effective measure for control of agricultural and medical pests, but evolution of resistance by pests threatens the sustainability of this approach. Resistance-conferring mutations sometimes impose fitness costs, which may drive subsequent evolution of compensatory modifier mutations alleviating the costs of resistance. However, how modifier mutations evolve and function to overcome the fitness cost of resistance still remains unknown. Here we show that overexpression of P450s not only confers imidacloprid resistance in the brown planthopper, Nilaparvata lugens, the most voracious pest of rice, but also leads to elevated production of reactive oxygen species (ROS) through metabolism of imidacloprid and host plant compounds. The inevitable production of ROS incurs a fitness cost to the pest, which drives the increase or fixation of the compensatory modifier allele T65549 within the promoter region of N. lugens peroxiredoxin (NlPrx) in the pest populations. T65549 allele in turn upregulates the expression of NlPrx and thus increases resistant individuals' ability to clear the cost-incurring ROS of any source. The frequent involvement of P450s in insecticide resistance and their capacity to produce ROS while metabolizing their substrates suggest that peroxiredoxin or other ROS-scavenging genes may be among the common modifier genes for alleviating the fitness cost of insecticide resistance.

Exposure of Helicoverpa armigera Larvae to Plant Volatile Organic Compounds Induces Cytochrome P450 Monooxygenases and Enhances Larval Tolerance to the Insecticide Methomyl

Plants release an array of volatile chemicals into the air to communicate with other organisms in the environment. Insect attack triggers emission of herbivore-induced plant volatiles (HIPVs). How insect herbivores use these odors to plan their detoxification systems is vital for insect adaptation to environmental xenobiotics. Here we show that the larvae of Helicoverpa armigera (Hübner), a broadly polyphagous lepidopteran herbivore, have the capacity to use plant volatiles as cues to upregulate multiple detoxification systems, including cytochrome P450 monooxygenases (P450s), for detoxification of insecticides. Olfactory exposure of the fifth instars to two terpene volatiles limonene and nerolidol, and two green-leaf volatiles 2-heptanone and cis-3-hexenyl acetate significantly reduced larval susceptibility to the insecticide methomyl. However, larval pretreatment with piperonyl butoxide (PBO), a known P450 inhibitor, neutralized the effects of volatile exposure. Furthermore, larval exposure to the four plant volatiles enhanced activities of P450 enzymes in midguts and fatbodies, and upregulated expression of CYP6B2, CYP6B6 and CYP6B7, P450s involved in detoxification of the insecticide. Larval exposure to 2-heptanone and limonene volatiles also enhanced activities of glutathione-s-transferase and carboxylesterase. Our findings suggest that olfactory exposure to HIPVs enhances larval insecticide tolerance via induction of detoxification P450s.