Origin and evolution of the CYP4G subfamily in insects, cytochrome P450 enzymes involved in cuticular hydrocarbon synthesis

Identification and expression dynamics of CYPome across different developmental stages of Maconellicoccus hirsutus (Green)

Maconellicoccus hirsutus is a highly polyphagous insect pest, posing a substantial threat to various crop sp., especially in the tropical and sub-tropical regions of the world. While extensive physiological and biological studies have been conducted on this pest, the lack of genetic information has hindered our understanding of the molecular mechanisms underlying its growth, development, and xenobiotic metabolism. The Cytochrome P450 gene, a member of the CYP gene superfamily ubiquitous in living organisms is associated with growth, development, and the metabolism of both endogenous and exogenous substances, contributing to the insect's adaptability in diverse environments. To elucidate the specific role of the CYP450 gene family in M. hirsutus which has remained largely unexplored, a de novo transcriptome assembly of the pink mealybug was constructed. A total of 120 proteins were annotated as CYP450 genes through homology search of the predicted protein sequences across different databases. Phylogenetic studies resulted in categorizing 120 CYP450 genes into four CYP clans. A total of 22 CYP450 families and 30 subfamilies were categorized, with CYP6 forming the dominant family. The study also revealed five genes (Halloween genes) associated with the insect hormone biosynthesis pathway. Further, the expression of ten selected CYP450 genes was studied using qRT-PCR across crawler, nymph, and adult stages, and identified genes that were expressed at specific stages of the insects. Thus, the findings of this study reveal the expression dynamics and possible function of the CYP450 gene family in the growth, development, and adaptive strategies of M. hirsutus which can be further functionally validated.

Chemical and transcriptomic diversity do not correlate with ascending levels of social complexity in the insect order Blattodea

Eusocial insects, such as ants and termites, are characterized by high levels of coordinated social organization. This is contrasted by solitary insects that display more limited forms of collective behavior. It has been hypothesized that this gradient in sociobehavioral sophistication is positively correlated with chemical profile complexity, due to a potentially increased demand for diversity in chemical communication mechanisms in insects with higher levels of social complexity. However, this claim has rarely been assessed empirically. Here, we compare different levels of chemical and transcriptomic complexity in selected species of the order Blattodea that represent different levels of social organization, from solitary to eusocial. We primarily focus on cuticular hydrocarbon (CHC) complexity, since it has repeatedly been demonstrated that CHCs are key signaling molecules conveying a wide variety of chemical information in solitary as well as eusocial insects. We assessed CHC complexity and divergence between our studied taxa of different social complexity levels as well as the differentiation of their respective repertoires of CHC biosynthesis gene transcripts. Surprisingly, we did not find any consistent pattern of chemical complexity correlating with social complexity, nor did the overall chemical divergence or transcriptomic repertoire of CHC biosynthesis genes reflect on the levels of social organization. Our results challenge the assumption that increasing social complexity is generally reflected in more complex chemical profiles and point toward the need for a more cautious and differentiated view on correlating complexity on a chemical, genetic, and social level.

Exploratory comparative transcriptomic analysis reveals potential gene targets associated with Cry1A.105 and Cry2Ab2 resistance in fall armyworm (Spodoptera frugiperda)

Genetically modified (GM) crops, expressing Bacillus thuringiensis (Bt) insecticidal toxins, have substantially transformed agriculture. Despite rapid adoption, their environmental and economic benefits face scrutiny due to unsustainable agricultural practices and the emergence of resistant pests like Spodoptera frugiperda, known as the fall armyworm (FAW). FAW's adaptation to Bt technology in corn and cotton compromises the long-term efficacy of Bt crops. To advance the understanding of the genetic foundations of resistance mechanisms, we conducted an exploratory comparative transcriptomic analysis of two divergent FAW populations. One population exhibited practical resistance to the Bt insecticidal proteins Cry1A.105 and Cry2Ab2, expressed in the genetically engineered MON-89Ø34 - 3 maize, while the other population remained susceptible to these proteins. Differential expression analysis supported that Cry1A.105 and Cry2Ab2 significantly affect the FAW physiology. A total of 247 and 254 differentially expressed genes were identified in the Cry-resistant and susceptible populations, respectively. By integrating our findings with established literature and databases, we underscored 53 gene targets potentially involved in FAW's resistance to Cry1A.105 and Cry2Ab2. In particular, we considered and discussed the potential roles of the differentially expressed genes encoding ABC transporters, G protein-coupled receptors, the P450 enzymatic system, and other Bt-related detoxification genes. Based on these findings, we emphasize the importance of exploratory transcriptomic analyses to uncover potential gene targets involved with Bt insecticidal proteins resistance, and to support the advantages of GM crops in the face of emerging challenges.

Fatty Acid Origin of Insect Pheromones

Pheromones are utilized to a great extent in insects. Many of these pheromones are biosynthesized through a pathway involving fatty acids. This chapter will provide examples where the biosynthetic pathways of fatty acid-derived pheromones have been studied in detail. These include pheromones from Lepidoptera, Coleoptera, and Hymenoptera. Many species of Lepidoptera utilize fatty acids as precursors to pheromones with a functional group that include aldehydes, alcohols, and acetate esters. In addition, the biosynthesis of hydrocarbons will be briefly examined because many insects utilize hydrocarbons or modified hydrocarbons as pheromones.

CYP4G subfamily genes mediate larval integument development in Spodoptera frugiperda

Cytochrome P450 (CYP) 4G subfamily is closely related to the synthesis of cuticular hydrocarbons, leading to the enhanced desiccation and insecticide resistance of pests. However, functions of CYP4Gs in larval integument development remain unknown in Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae), which is a major transboundary migratory pest and become a common pest in China. On the basis of the genome and transcriptome datasets of S. frugiperda, CYP4G74, CYP4G75, CYP4G108, and CYP4G109 were identified, which contained the conserved domains of P450s and CYP4Gs. The spatial and temporal expression analysis showed that CYP4G74 and CYP4G75 were significantly highly expressed in adults and larval integuments, while CYP4G108 and CYP4G109 had low expressions in larval integuments. After silencing CYP4G74 and CYP4G75 by RNA interference, abnormal integument development occurred in larvae, some of which became smaller and dead, indicating important roles of CYP4G74 and CYP4G75 in the synthesis and development of integuments. The results clarify the functions of CYP4Gs in S. frugiperda and provide potential targets for the control of this pest.

Transcriptome-Wide Identification of Cytochrome P450s in Tea Black Tussock Moth (Dasychira baibarana) and Candidate Genes Involved in Type-II Sex Pheromone Biosynthesis

The tea black tussock moth (Dasychira baibarana), a devastating pest in Chinese tea plantations, uses a ternary Type-II pheromone blend containing (3Z,6Z)-cis-9,10-epoxyhenicosa-3,6-diene (Z3,Z6,epo9-21:H), (3Z,6Z,11E)-cis-9,10-epoxyhenicosa-3,6,11-triene (Z3,Z6,epo9,E11-21:H), and (3Z,6Z)-henicosa-3,6-dien-11-one (Z3,Z6-21:11-one) for mate communication. To elucidate the P450 candidates associated with the biosynthesis of these sex pheromone components, we sequenced the female D. baibarana pheromone gland and the abdomen excluding the pheromone gland. A total of 75 DbP450s were identified. Function annotation suggested six CYPs were orthologous genes that are linked to molting hormone metabolism, and eight antennae specifically and significantly up-regulated CYPs may play roles in odorant processing. Based on a combination of comparative RNAseq, phylogenetic, and tissue expression pattern analysis, one CYP4G with abdomen specifically predominant expression pattern was likely to be the P450 decarbonylase, while the pheromone-gland specifically and most abundant CYP341B65 was the most promising epoxidase candidate for the D. baibarana sex pheromone biosynthesis. Collectively, our research laid a valuable basis not only for further functional elucidation of the candidate P450 decarbonylase and epoxidase for the sex pheromone biosynthesis but also for understanding the physiological functions and functional diversity of the CYP gene superfamily in the D. baibarana.

Insights into unique features of Drosophila CYP4G enzymes

The cytochrome P450 enzymes of the CYP4G subfamily are some of the most intriguing insect P450s in terms of structure and function. In Drosophila, CYP4G1 is highly expressed in the oenocytes and is the last enzyme in the biosynthesis of cuticular hydrocarbons, while CYP4G15 is expressed in the brain and is of unknown function. Both proteins have a CYP4G-specific and characteristic amino acid sequence insertion corresponding to a loop between the G and H helices whose function is unclear. Here we address these enigmatic structural and functional features of Drosophila CYP4Gs. First, we used reverse genetics to generate D. melanogaster strains in which all or part of the CYP4G-specific loop was removed from CYP4G1. We showed that the full loop was not needed for proper folding of the P450, but it is essential for function, and that just a short stretch of six amino acids is required for the enzyme's ability to make hydrocarbons. Second, we confirmed by immunocytochemistry that CYP4G15 is expressed in the brain and showed that it is specifically associated with the cortex glia cell subtype. We then expressed CYP4G15 ectopically in oenocytes, revealing that it can produce of a blend of hydrocarbons, albeit to quantitatively lower levels resulting in only a partial rescue of CYP4G1 knockdown flies. The CYP4G1 structural variants studied here should facilitate the biochemical characterization of CYP4G enzymes. Our results also raise the question of the putative role of hydrocarbons and their synthesis by cortex glial cells.

The Molecular Resistance Mechanisms of European Earwigs from Apple Orchards Subjected to Different Management Strategies

To date, apple orchards are among the most treated crops in Europe with up to 35 chemical treatments per year. Combining control methods that reduce the number of pesticide treatments is essential for agriculture and more respectful of the environment, and the use of predatory insects such as earwigs may be valuable to achieve this goal. European earwigs, Forficula auricularia (Dermaptera: Forficulidae) are considered beneficial insects in apple orchards where they can feed on many pests like aphids. The aim of this study was to investigate the potential impact of orchards' insecticide treatments on resistance-associated molecular processes in natural populations of earwigs. Because very few molecular data are presently available on earwigs, our first goal was to identify earwig resistance-associated genes and potential mutations. Using earwigs from organic, integrated pest management or conventional orchards, we identified mutations in acetylcholinesterase 2, α1 and β2 nicotinic acetylcholine receptors. In addition, the expression level of these targets and of some essential detoxification genes were monitored using RT-qPCR. Unexpectedly, earwigs collected in organic orchards showed the highest expression for acetylcholinesterase 2. Four cytochromes P450, one esterase and one glutathione S-transferases were over-expressed in earwigs exposed to various management strategies in orchards. This first study on resistance-associated genes in Forficula auricularia paves the way for future experimental studies aimed at better understanding the potential competition between natural enemies in apple orchards in order to optimize the efficiency of biocontrol.

Inducible Cytochrome P450s in the Fat Body and Malpighian Tubules of the Polyphagous Pests of Spodoptera litura Confer Xenobiotic Tolerance

Cytochrome P450 plays vital roles in detoxifying xenobiotics. In this study, SlCYP340A and SlCYP340L expression in the Spodoptera litura fat body and SlCYP332A1, SlCYP6AB12, SlCYP6AB58, SlCYP6AB59, and SlCYP6AN4 expression in the Malpighian tubules were significantly upregulated after cyantraniliprole exposure, and SlCYP6AB58 and SlCYP6AB59 expression levels were simultaneously increased in the Malpighian tubules after gossypol treatment. Drosophila ectopically expressing candidate P450 genes showed that SlCYP332A1, SlCYP6AB12, SlCYP6AB59, SlCYP6AN4, and SlCYP340A conferred cyantraniliprole tolerance. The overexpression of SlCYP6AB58 and SlCYP6AB59 in Drosophila increased the number of eggs laid under the gossypol treatment. Moreover, the knockdown of SlCYP332A1, SlCYP6AB12, SlCYP6AB59, SlCYP6AN4, and SlCYP340A increased S. litura mortality under the cyantraniliprole treatment. Homology modeling and molecular docking results suggested that candidate P450 has the potential to bind with cyantraniliprole. These results indicate that the CYP3 and CYP4 genes participate in cyantraniliprole detoxification and that SlCYP6AB59 may be simultaneously involved in the gossypol tolerance of S. litura.

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

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

Aliens in the CYPome of the black fungus gnat, Bradysia coprophila

The diverse cytochrome P450 enzymes of insects play essential physiological roles and also play important roles in the metabolism of environmental chemicals such as insecticides. We manually curated the complement of P450 (CYP) genes, or CYPome, of the black fungus gnat, Bradysia (Sciara) coprophila (Diptera, Sciaroidea), a species with a variable number of chromosomes. This CYPome carries two types of "alien" P450 genes. The first type of alien P450s was found among the 163 CYP genes of the core genome (autosomes and X). They consist of 28 sequences resulting from horizontal gene transfer, with closest sequences not found in insects, but in other arthropods, often Collembola. These genes are not contaminants, because they are expressed genes with introns, found in synteny with regular dipteran genes, also found in B. odoriphaga and B. hygida. Two such "alien" genes are representatives of CYP clans not otherwise found in insects, a CYP53 sequence related to fungal CYP53 genes, and a CYP19-like sequence similar to some collembolan sequences but of unclear origin. The second type of alien P450s are represented by 99 sequences from germline-restricted chromosomes (GRC). While most are P450 pseudogenes, 33 are apparently intact, with half being more closely related to P450s from Cecidomyiidae than from Sciaridae, thus supporting the hypothesis of a cross-family hybridization origin of the GRC.

Cytochrome P450 gene CYP6BQ8 mediates terpinen-4-ol susceptibility in the red flour beetle, Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae)

Cytochrome P450 proteins (CYPs) in insects can encode various detoxification enzymes and catabolize heterologous substances, conferring tolerance to insecticides. This study describes the identification of a P450 gene (CYP6BQ8) from Tribolium castaneum (Herbst) and investigation of its spatiotemporal expression profile and potential role in the detoxification of terpinen-4-ol, a component of plant essential oils. The developmental expression profile showed that TcCYP6BQ8 expression was relatively higher in early- and late-larval stages of T. castaneum compared with other developmental stages. Tissue expression profiles showed that TcCYP6BQ8 was mainly expressed in the head and integument of both larvae and adults. The expression profiling of TcCYP6BQ8 in developmental stages and tissues is closely related to the detoxification of heterologous substances. TcCYP6BQ8 expression was significantly induced after exposure to terpinen-4-ol, and RNA interference against TcCYP6BQ8 increased terpinen-4-ol-induced larval mortality from 47.78 to 66.67%. This indicates that TcCYP6BQ8 may be involved in T. castaneum's metabolism of terpinen-4-ol. Correlation investigation between the CYP6BQ8 gene and terpinen-4-ol resistance in T. castaneum revealed that the TcCYP6BQ8 gene was one of the factors behind T. castaneum's resistance to terpinen-4-ol. This discovery may provide a new theoretical foundation for future regulation of T. castaneum.

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.

Intrasexual cuticular hydrocarbon dimorphism in a wasp sheds light on hydrocarbon biosynthesis genes in Hymenoptera

Cuticular hydrocarbons (CHCs) cover the cuticle of insects and serve as desiccation barrier and as semiochemicals. While the main enzymatic steps of CHC biosynthesis are well understood, few of the underlying genes have been identified. Here we show how exploitation of intrasexual CHC dimorphism in a mason wasp, Odynerus spinipes, in combination with whole-genome sequencing and comparative transcriptomics facilitated identification of such genes. RNAi-mediated knockdown of twelve candidate gene orthologs in the honey bee, Apis mellifera, confirmed nine genes impacting CHC profile composition. Most of them have predicted functions consistent with current knowledge of CHC metabolism. However, we found first-time evidence for a fatty acid amide hydrolase also influencing CHC profile composition. In situ hybridization experiments furthermore suggest trophocytes participating in CHC biosynthesis. Our results set the base for experimental CHC profile manipulation in Hymenoptera and imply that the evolutionary origin of CHC biosynthesis predates the arthropods' colonization of land.

The Chromosome-Level Genome of Hestina assimilis (Lepidoptera: Nymphalidae) Reveals the Evolution of Saprophagy-Related Genes in Brush-Footed Butterflies

Most butterflies feed on nectar, while some saprophagous butterflies forage on various non-nectar foods. To date, little is known about the genomic and molecular shifts associated with the evolution of the saprophagous feeding strategy. Here, we assembled the high-quality chromosome-level genome of Hestina assimilis to explore its saprophagous molecular and genetic mechanisms. This chromosome-level genome of H. assimilis is 412.82 Mb, with a scaffold N50 of 15.70 Mb. In total, 98.11% of contigs were anchored to 30 chromosomes. Compared with H. assimilis and other Nymphalidae butterflies, the genes of metabolism and detoxification experienced expansions. We annotated 80 cytochrome P450 (CYP) genes in the H. assimilis genome, among which genes belonging to the CYP4 subfamily were significantly expanded (p < 0.01). These P450 genes were unevenly distributed and mainly concentrated on chromosomes 6-9. We identified 33 olfactory receptor (OR), 20 odorant-binding protein (OBP), and six gustatory receptor (GR) genes in the H. assimilis genome, which were fewer than in the nectarivorous Danaus plexippus. A decreased number of OBP, OR, and GR genes implied that H. assimilis should resort less to olfaction and gustation than their nectarivorous counterparts, which need highly specialized olfactory and gustatory functions. Moreover, we found one site under positive selection occurred in residue 996 (phenylalanine) of GR genes exclusive to H. assimilis, which is conservative in most lineages. Our study provides support for the adaptive evolution of feeding habits in butterflies.

The genome sequence of the Neotropical brown stink bug, Euschistus heros provides insights into population structure, demographic history and signatures of adaptation

The Neotropical brown stink bug, Euschistus heros, is a major pest of soybean in South America. The importance of E. heros as a pest has grown significantly in recent times due to increases in its abundance and range, and the evolution of insecticide resistance. Recent work has begun to examine the genetic diversity, population structure, and genetic mechanisms of insecticide resistance in E. heros. However, to date, investigation of these topics has been hampered by a lack of genomic resources for this species. Here we address this need by assembling a high-quality draft genome for E. heros. We used a combination of short and long read sequencing to assemble an E. heros genome of 1.4 Gb comprising 906 contigs with a contig N50 of 3.5 MB. We leveraged this new genomic resource, in combination with genotyping by sequencing, to explore genetic diversity in populations of this species in Brazil and identify genetic loci in the genome which are under selection. Our genome-wide analyses, confirm that there are two populations of E. heros co-occurring in different geographical regions in Brazil, and that, in certain regions of the country these populations are hybridizing. We identify several regions of the genome as under selection, including markers associated with putative insecticide resistance genes. Taken together, the new genomic resources generated in this study will accelerate research into fundamental aspects of stinkbug biology and applied aspects relating to the sustainable control of a highly damaging crop pest.

CYP4G100 contributes to desiccation resistance by mediating cuticular hydrocarbon synthesis in Bactrocera dorsalis

The oriental fruit fly Bactrocera dorsalis (Hendel) is expanding its distribution to higher latitudes. Our goal in this study was to understand how B. dorsalis adapts to higher latitude environments that are more arid than tropical regions. Cuticular hydrocarbons (CHCs) on the surface of the epicuticle in insects act as a hydrophobic barrier against water loss. The essential decarbonylation reaction in CHC synthesis is catalysed by CYP4G, a cytochrome P450 subfamily protein. Hence, in B. dorsalis it is necessary to clarify the function of the CYP4G gene and its role in desiccation resistance. CYP4G100 was identified in the B. dorsalis genome. The complete open reading frame (ORF) encodes a CYP4 family protein (552 amino acid residues) that has the CYP4G-specific insertion. This CYP4G gene was highly expressed in adults, especially in the oenocyte-rich peripheral fat body. The gene can be induced by desiccation treatment, suggesting its role in CHC synthesis and waterproofing. Silencing of CYP4G100 resulted in a decrease of CHC levels and the accumulation of triglycerides. It also increased water loss and resulted in higher desiccation susceptibility. CYP4G100 is involved in hydrocarbon synthesis and contributes to cuticle waterproofing to help B. dorsalis resist desiccation in arid environments.

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.

Fatty acyl-CoA reductase influences wax biosynthesis in the cotton mealybug, Phenacoccus solenopsis Tinsley

Mealybugs are highly aggressive to a diversity of plants. The waxy layer covering the outermost part of the integument is an important protective defense of these pests. However, the molecular mechanisms underlying wax biosynthesis in mealybugs remain largely unknown. Here, we analyzed multi-omics data on wax biosynthesis by the cotton mealybug, Phenacoccus solenopsis Tinsley, and found that a fatty acyl-CoA reductase (PsFAR) gene, which was highly expressed in the fat bodies of female mealybugs, contributed to wax biosynthesis by regulating the production of the dominant chemical components of wax, cuticular hydrocarbons (CHCs). RNA interference (RNAi) against PsFAR by dsRNA microinjection and allowing mealybugs to feed on transgenic tobacco expressing target dsRNA resulted in a reduction of CHC contents in the waxy layer, and an increase in mealybug mortality under desiccation and deltamethrin treatments. In conclusion, PsFAR plays crucial roles in the wax biosynthesis of mealybugs, thereby contributing to their adaptation to water loss and insecticide stress.

The role of a fatty acyl-CoA reductase (PsFAR) in wax biosynthesis of cotton mealybug is investigated, RNAi against PsFAR resulted in insects with lower generation of waxy filaments and higher mortality under desiccation and deltamethrin treatments.

Silencing of Cytochrome P450 Gene AgoCYP6CY19 Reduces the Tolerance to Host Plant in Cotton- and Cucumber-Specialized Aphids, Aphis gossypii

Cytochrome P450 monooxygenases play important roles in insect metabolism and detoxification of toxic plant substances. However, the function of CYP6 family genes in degrading plant toxicants in Aphis gossypii has yet to be elucidated. In this study, AgoCYP6CY19, an A. gossypii CYP gene that differentially expresses in cotton- and cucumber-specialized aphids, was characterized. Spatiotemporal expression profiling revealed that AgoCYP6CY19 expression was higher in second instar nymph and 7 day old adults than in other developmental stages. Although the expression of AgoCYP6CY19 was significantly higher in cotton-specialized aphids, AgoCYP6CY19 silencing significantly increased larval and adult mortality and reduced total fecundity in both cotton- and cucumber-specialized aphids. What is more, the expression of AgoCYP6CY19 was significantly induced after the cotton-specialized and cucumber-specialized aphids fed on epigallocatechin gallate (EGCG) and cucurbitacin B (CucB), respectively. These findings demonstrate that AgoCYP6CY19 plays a pivotal role in toxic plant substance detoxification and metabolism. Functional knowledge about plant toxicity tolerance genes in this major pest can provide new insights into insect detoxification of toxic plant substances and insecticides and offer new targets for agricultural pest control strategies.

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

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

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.

A CYP380C10 gene is required for waterproofing and water retention in the insect integument

Cuticular hydrocarbons (CHCs) are important components in the integument of insects and are required for development and survival. Insect-specific CYP4G subfamily, of the P450 enzymes, catalyze the oxidative decarbonylation step in the biosynthesis of CHCs. Here, we characterized CYP380C10 gene function in a Hemiptera rice pest, Nilaparvata lugens. We used RNA interference-mediated expression silencing to reveal that NlCYP380C10 played a key role in waterproofing and water-retention in the integument of N. lugens. Knockdown of NlCYP380C10 significantly reduced body weight and caused mortality. Scanning electron microscopy showed the loss of the lipid layer on the surface of the abdominal cuticle of the dsNlCYP380C10-injected adults. Furthermore, CHC profile analysis revealed that NlCYP380C10 knockdown significantly decreased the amounts of CHCs in adult females. This suggested that NlCYP380C10 was involved in CHC biosynthesis. Reduction of CHC content caused the loss of the intact lipid layer of the cuticle, which resulted in loss of the waterproofing and water-retention functions. This led to failure of molting and eclosion. Our findings expanded the knowledge of CHC biosynthesis in the insect integument and led to a better understanding of the functional roles of CYP450 genes involved in waterproofing and water-retention in insects.

Cytochrome P450 Genes of the CYP4 Clan and Pyrethroid Resistance in Chagas Disease Vectors

Triatomine insects are vectors of the protozoan Trypanosoma cruzi, the causative agent of Chagas disease. Although residual pyrethroid spraying has been a successful vector control strategy for many years, a growing number of pyrethroid-resistance foci is being documented, mainly in Triatoma infestans, that led to failures in vector elimination. Insecticide resistance is a multifactorial phenomenon that often implies a combination of three different mechanisms: increased insecticide detoxification, reduced affinity of the site of action, and reduced insecticide penetration through the cuticle. All three mechanisms were reported in pyrethroid-resistant T. infestans. Cytochrome P450s are enzymes involved in the metabolism of xenobiotics and endogenous chemicals. They are encoded by CYP genes and classified into different families and clans. In triatomines, the CYP4 clan is divided in two families, CYP3093 and CYP4, and both exhibit genome-wide, triatomine-specific gene expansions. Some members from each family have been reported to be involved in two of the mechanisms mentioned above, i.e., they participate in insecticide detoxification in different organs and tissues, and in the synthesis of cuticular hydrocarbons, which ultimately can contribute to a reduced insecticide penetration. The aim of this manuscript is to review the current state of knowledge of P450 genes belonging to the CYP4 clan in triatomines and to highlight their potential role in insecticide resistance.

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.

Update of the keratin gene family: evolution, tissue-specific expression patterns, and relevance to clinical disorders

Intermediate filament (IntFil) genes arose during early metazoan evolution, to provide mechanical support for plasma membranes contacting/interacting with other cells and the extracellular matrix. Keratin genes comprise the largest subset of IntFil genes. Whereas the first keratin gene appeared in sponge, and three genes in arthropods, more rapid increases in keratin genes occurred in lungfish and amphibian genomes, concomitant with land animal-sea animal divergence (~ 440 to 410 million years ago). Human, mouse and zebrafish genomes contain 18, 17 and 24 non-keratin IntFil genes, respectively. Human has 27 of 28 type I "acidic" keratin genes clustered at chromosome (Chr) 17q21.2, and all 26 type II "basic" keratin genes clustered at Chr 12q13.13. Mouse has 27 of 28 type I keratin genes clustered on Chr 11, and all 26 type II clustered on Chr 15. Zebrafish has 18 type I keratin genes scattered on five chromosomes, and 3 type II keratin genes on two chromosomes. Types I and II keratin clusters-reflecting evolutionary blooms of keratin genes along one chromosomal segment-are found in all land animal genomes examined, but not fishes; such rapid gene expansions likely reflect sudden requirements for many novel paralogous proteins having divergent functions to enhance species survival following sea-to-land transition. Using data from the Genotype-Tissue Expression (GTEx) project, tissue-specific keratin expression throughout the human body was reconstructed. Clustering of gene expression patterns revealed similarities in tissue-specific expression patterns for previously described "keratin pairs" (i.e., KRT1/KRT10, KRT8/KRT18, KRT5/KRT14, KRT6/KRT16 and KRT6/KRT17 proteins). The ClinVar database currently lists 26 human disease-causing variants within the various domains of keratin proteins.

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.

Gut transcriptome of two bark beetle species stimulated with the same kairomones reveals molecular differences in detoxification pathways

Dendroctonus bark beetles are the most destructive agents in coniferous forests. These beetles come into contact with the toxic compounds of their host's chemical defenses throughout their life cycle, some of which are also used by the insects as kairomones to select their host trees during the colonization process. However, little is known about the molecular mechanisms by which the insects counteract the toxicity of these compounds. Here, two sibling species of bark beetles, D. valens and D. rhizophagus, were stimulated with vapors of a blend of their main kairomones (α-pinene, β-pinene and 3-carene), in order to compare the transcriptional response of their gut. A total of 48 180 unigenes were identified in D. valens and 43 704 in D. rhizophagus, in response to kairomones blend. The analysis of differential gene expression showed a transcriptional response in D. valens (739 unigenes, 0.58–10.36 Log2FC) related to digestive process and in D. rhizophagus (322 unigenes 0.87–13.08 Log2FC) related to xenobiotics metabolism. The expression profiles of detoxification genes mainly evidenced the up-regulation of COEs and GSTs in D. valens, and the up-regulation of P450s in D. rhizophagus. Results suggest that terpenes metabolism comes accompanied by an integral hormetic response, result of compensatory mechanisms, including the activation of other metabolic pathways, to ensure the supply of energy and the survival of organisms which is specific for each species, according to its life history and ecological strategy.

CYP4G8 is responsible for the synthesis of methyl-branched hydrocarbons in the polyphagous caterpillar of Helicoverpa armigera

Insect cuticular hydrocarbons (CHCs) have dual functions as physical barrier and chemical signals. The last step of CHC biosynthesis is known to be catalyzed by cytochrome P450 CYP4G in a number of insects. Until recently, studies on CYP4Gs in the context of functional evolution are rare. In this study, we analyzed sequence similarity and temporal-spatial expression patterns of the five CYP4G genes in the cotton bollworm Helicoverpa armigera, an important agricultural pest and also typical representative of lepidopteran insects. Moreover, the CRISPR/Cas9-induced knockout was used to clarify the roles of the five CYP4Gs in CHC biosynthesis. Temporal-spatial expression patterns revealed that CYP4G8 was highly expressed at all developmental stages and in most tissues examined. Larvae with CYP4G8 knocked out could not produce methyl-branched CHCs and failed to pupate, while larvae with the other four CYP4G genes knocked out (4G1-type-KO) showed no significant changes in their CHC profiles, weight gain and survival. Comparative transcriptomics revealed that knocking out CYP4G8 affected the global gene expression in larvae, especially down-regulated the expression of genes in the fatty acid biosynthetic pathway, while no significant change in 4G1-type-KO transcriptome was observed. These findings indicate that the five members of the CYP4G subfamily have undergone functional divergence: CYP4G8 maintains the essential function in CHC biosynthesis, while the function of the other four CYP4G genes remains unclear. Intriguingly, CYP4G8 has evolved to be a P450 enzyme responsible for the synthesis of larval methyl-branched hydrocarbons. The observation that CYP4G8 knockout is lethal strongly suggest that CYP4G8 may serve as a candidate target for the development of insecticidal agents for the control of cotton bollworms.

Evolutionary assembly of cooperating cell types in an animal chemical defense system

How the functions of multicellular organs emerge from the underlying evolution of cell types is poorly understood. We deconstructed evolution of an organ novelty: a rove beetle gland that secretes a defensive cocktail. We show how gland function arose via assembly of two cell types that manufacture distinct compounds. One cell type, comprising a chemical reservoir within the abdomen, produces alkane and ester compounds. We demonstrate that this cell type is a hybrid of cuticle cells and ancient pheromone and adipocyte-like cells, executing its function via a mosaic of enzymes from each parental cell type. The second cell type synthesizes benzoquinones using a chimera of conserved cellular energy and cuticle formation pathways. We show that evolution of each cell type was shaped by coevolution between the two cell types, yielding a potent secretion that confers adaptive value. Our findings illustrate how cooperation between cell types arises, generating new, organ-level behaviors.

Detoxification gene families in Phylloxera: Endogenous functions and roles in response to the environment

Phylloxera, Daktulosphaira vitifoliae, is an agronomic pest that feeds monophagously on grapevine, Vitis spp. host plants. Phylloxera manipulates primary and secondary plant metabolism to establish either leaf or root galls. We manually annotated 198 detoxification genes potentially involved in plant host manipulation, including cytochrome P450 (66 CYPs), carboxylesterase (20 CCEs), glutathione-S-transferase (10 GSTs), uridine diphosphate-glycosyltransferase (35 UGTs) and ABC transporter (67 ABCs) families. Transcriptomic expression patterns of these detoxification genes were analyzed for root and leaf galls. In addition to these transcriptomic analyses, we reanalyzed recent data from L1 and L2-3 stages feeding on tolerant and resistant rootstock. Data from two agricultural pest aphids, the generalist Myzus persicae and the Fabaceae specialist Acyrthosiphon pisum, and from the true bug vector of Chagas disease, Rhodnius prolixus, were used to perform phylogenetic analyses for each detoxification gene family. We found expansions of several gene sub-families in the genome of D. vitifoliae. Phylogenetically close genes were found to be organized in clusters in the same genomic position and orientation suggesting recent successive duplications. These results highlight the roles of the phylloxera detoxification gene repertoire in insect physiology and in adaptation to plant secondary metabolites, and provide gene candidates for further functional analyses.

Comparative analysis of the detoxification gene inventory of four major Spodoptera pest species in response to xenobiotics

The genus Spodoptera (Lepidoptera: Noctuidae) comprises some of the most polyphagous and destructive agricultural pests worldwide. The success of many species of this genus is due to their striking abilities to adapt to a broad range of host plants. Superfamilies of detoxification genes play a crucial role in the adaption to overcome plant defense mechanisms mediated by numerous secondary metabolites and toxins. Over the past decade, a substantial amount of expression data in Spodoptera larvae was produced for those genes in response to xenobiotics such as plant secondary metabolites, but also insecticide exposure. However, this information is scattered throughout the literature and in most cases does not allow to clearly identify candidate genes involved in host-plant adaptation and insecticide resistance. In the present review, we analyzed and compiled information on close to 600 pairs of inducers (xenobiotics) and induced genes from four main Spodoptera species: S. exigua, S. frugiperda, S. littoralis and S. litura. The cytochrome P450 monooxygenases (P450s; encoded by CYP genes) were the most upregulated detoxification genes across the literature for all four species. Most of the data was provided from studies on S. litura, followed by S. exigua, S. frugiperda and S. littoralis. We examined whether these detoxification genes were reported for larval survival under xenobiotic challenge in forward and reverse genetic studies. We further analyzed whether biochemical assays were carried out showing the ability of corresponding enzymes and transporters to breakdown and excrete xenobiotics, respectively. This revealed a clear disparity between species and the lack of genetic and biochemical information in S. frugiperda. Finally, we discussed the biological importance of detoxification genes for this genus and propose a workflow to study the involvement of these enzymes in an ecological and agricultural context.

Genome-wide gene expression profiles of the pea aphid (Acyrthosiphon pisum) under cold temperatures provide insights into body color variation

Cold temperatures are one of the factors influencing color polymorphisms in Acyrthosiphon pisum, resulting in a change from a red to greenish color. Here we characterized gene expression profiles of A. pisum under different low temperatures (1°C, 4°C, 8°C, and 14°C) and durations (3, 6, 12, and 24 h). The number of differentially expressed genes (DEGs) increased as temperatures decreased and time increased, but only a small number of significant DEGs were identified. Genes involved in pigment metabolism were downregulated. An interaction network analysis for 506 common DEGs in comparisons among aphids exposed to 1°C for four durations indicated that a cytochrome P450 gene (CYP, LOC112935894) significantly downregulated may interact with a carotenoid metabolism gene (LOC100574964), similar to other genes encoding CYP, lycopene dehydrogenase and fatty acid synthase. We proposed that the body color shift in A. pisum responding to low temperatures may be regulated by CYPs.

RNAi by Soaking Aedes aegypti Pupae in dsRNA

RNA-interference (RNAi) is a standard technique for functional genomics in adult mosquitoes. However, RNAi in immature, aquatic mosquito stages has been challenging. Several studies have shown successful larval RNAi, usually in combination with a carrier molecule. Except for one study in malaria mosquito, Anopheles gambiae, none of the previous studies has explored RNAi in mosquito pupae. Even in the study that used RNAi in pupae, double stranded RNA (dsRNA) was introduced by microinjection. Here, we describe a successful method by soaking pupae in water containing dsRNA without any carrier or osmotic challenge. The knockdown persisted into adulthood. We expect that this simple procedure will be useful in the functional analysis of genes that highly express in pupae or newly emerged adults.

Genetic basis of chemical communication in eusocial insects

Social behavior is one of the most fascinating and complex behaviors in humans and animals. A fundamental process of social behavior is communication among individuals. It relies on the capability of the nervous system to sense, process, and interpret various signals (e.g., pheromones) and respond with appropriate decisions and actions. Eusocial insects, including ants, some bees, some wasps, and termites, display intriguing cooperative social behavior. Recent advances in genetic and genomic studies have revealed key genes that are involved in pheromone synthesis, chemosensory perception, and physiological and behavioral responses to varied pheromones. In this review, we highlight the genes and pathways that regulate queen pheromone-mediated social communication, discuss the evolutionary changes in genetic systems, and outline prospects of functional studies in sociobiology.

Cuticle Hydrocarbons Show Plastic Variation under Desiccation in Saline Aquatic Beetles

In the context of aridification in Mediterranean regions, desiccation resistance and physiological plasticity will be key traits for the persistence of aquatic insects exposed to increasing desiccation stress. Control of cuticular transpiration through changes in the quantity and composition of epicuticular hydrocarbons (CHCs) is one of the main mechanisms of desiccation resistance in insects, but it remains largely unexplored in aquatic ones. We studied acclimation responses to desiccation in adults of two endemic water beetles from distant lineages living in Mediterranean intermittent saline streams: Enochrus jesusarribasi (Hydrophilidae) and Nebrioporus baeticus (Dytiscidae). Cuticular water loss and CHC composition were measured in specimens exposed to a prior non-lethal desiccation stress, allowed to recover and exposed to a subsequent desiccation treatment. E. jesusarribasi showed a beneficial acclimation response to desiccation: pre-desiccated individuals reduced cuticular water loss rate in a subsequent exposure by increasing the relative abundance of cuticular methyl-branched compounds, longer chain alkanes and branched alkanes. In contrast, N. baeticus lacked acclimation capacity for controlling water loss and therefore may have a lower physiological capacity to cope with increasing aridity. These results are relevant to understanding biochemical adaptations to drought stress in inland waters in an evolutionary and ecological context.

Primary Metabolism co-Opted for Defensive Chemical Production in the Carabid Beetle, Harpalus pensylvanicus

Of the approximately one million described insect species, ground beetles (Coleoptera: Carabidae) have long captivated the attention of evolutionary biologists due to the diversity of defensive compounds they synthesize. Produced using defensive glands in the abdomen, ground beetle chemicals represent over 250 compounds including predator-deterring formic acid, which has evolved as a defensive strategy at least three times across Insecta. Despite being a widespread method of defense, formic acid biosynthesis is poorly understood in insects. Previous studies have suggested that the folate cycle of one-carbon (C1) metabolism, a pathway involved in nucleotide biosynthesis, may play a key role in defensive-grade formic acid production in ants. Here, we report on the defensive gland transcriptome of the formic acid-producing ground beetle Harpalus pensylvanicus. The full suite of genes involved in the folate cycle of C1 metabolism are significantly differentially expressed in the defensive glands of H. pensylvanicus when compared to gene expression profiles in the rest of the body. We also find support for two additional pathways potentially involved in the biosynthesis of defensive-grade formic acid, the kynurenine pathway and the methionine salvage cycle. Additionally, we have found an array of differentially expressed genes in the secretory lobes involved in the biosynthesis and transport of cofactors necessary for formic acid biosynthesis, as well as genes presumably involved in the detoxification of secondary metabolites including formic acid. We also provide insight into the evolution of the predominant gene family involved in the folate cycle (MTHFD) and suggest that high expression of folate cycle genes rather than gene duplication and/or neofunctionalization may be more important for defensive-grade formic acid biosynthesis in H. pensylvanicus. This provides the first evidence in Coleoptera and one of a few examples in Insecta of a primary metabolic process being co-opted for defensive chemical biosynthesis. Our results shed light on potential mechanisms of formic acid biosynthesis in the defensive glands of a ground beetle and provide a foundation for further studies into the evolution of formic acid-based chemical defense strategies in insects.

Knockdown of CYP4PR1, a cytochrome P450 gene highly expressed in the integument tissue of Triatoma infestans, increases susceptibility to deltamethrin in pyrethroid-resistant insects

Metabolic resistance to chemical insecticides implies a greater capacity to detoxify insecticides due to an increase in the expression of genes and/or in the activity of enzymes related to detoxification metabolism. The insect integument is known to participate as the cuticular penetration factor of resistance, but recently this tissue was also linked with metabolic resistance due to P450-dependent detoxification in the Chagas disease vector Triatoma infestans. The objectives of this study were i) to name and classify all P450s known to date in T. infestans, ii) to characterise one of them, CYP4PR1, representing the first member of a new cytochrome P450 subfamily described in insects, and iii) to investigate the potential role of CYP4PR1 in metabolic resistance to deltamethrin in T. infestans. We found that CYP4PR1 is expressed almost exclusively in the integument tissue, and its expression was not induced by deltamethrin. Knockdown of CYP4PR1 by RNA interference in pyrethroid-resistant nymphs caused a significant increment in insect mortality after topical application of two different doses of deltamethrin. These results support the role of the integument on metabolic resistance and suggest that CYP4PR1 might contribute to resistance in integument tissue of T. infestans.

Advances in deciphering the genetic basis of insect cuticular hydrocarbon biosynthesis and variation

Cuticular hydrocarbons (CHCs) have two fundamental functions in insects. They protect terrestrial insects against desiccation and serve as signaling molecules in a wide variety of chemical communication systems. It has been hypothesized that these pivotal dual traits for adaptation to both desiccation and signaling have contributed to the considerable evolutionary success of insects. CHCs have been extensively studied concerning their variation, behavioral impact, physiological properties, and chemical compositions. However, our understanding of the genetic underpinnings of CHC biosynthesis has remained limited and mostly biased towards one particular model organism (Drosophila). This rather narrow focus has hampered the establishment of a comprehensive view of CHC genetics across wider phylogenetic boundaries. This review attempts to integrate new insights and recent knowledge gained in the genetics of CHC biosynthesis, which is just beginning to incorporate work on more insect taxa beyond Drosophila. It is intended to provide a stepping stone towards a wider and more general understanding of the genetic mechanisms that gave rise to the astonishing diversity of CHC compounds across different insect taxa. Further research in this field is encouraged to aim at better discriminating conserved versus taxon-specific genetic elements underlying CHC variation. This will be instrumental in greatly expanding our knowledge of the origins and variation of genes governing the biosynthesis of these crucial phenotypic traits that have greatly impacted insect behavior, physiology, and evolution.

Disruption of the cytochrome P450 CYP6BQ7 gene reduces tolerance to plant toxicants in the red flour beetle, Tribolium castaneum

In insects, the cytochrome P450 CYP6B family plays key roles in the detoxification of toxic plant substances. However, the function of CYP6 family genes in degrading plant toxicants in Tribolium castaneum, an extremely destructive global storage pest, have yet to be elucidated. In this study, a T. castaneum CYP gene, TcCYP6BQ7, was characterized. TcCYP6BQ7 expression was significantly induced after exposure to essential oil of the plant Artemisia vulgaris (EOAV). Spatiotemporal expression profiling revealed that TcCYP6BQ7 expression was higher in larval and adult stages of T. castaneum than in other developmental stages, and that TcCYP6BQ7 was predominantly expressed in the brain and hemolymph from the late larval stage. TcCYP6BQ7 silencing by RNA interference increased larvae mortality in response to EOAV from 49.67% to 71.67%, suggesting that this gene is associated with plant toxicant detoxification. Combined results from this study indicate that the CYP6 family gene TcCYP6BQ7 likely plays a pivotal role in influencing the susceptibility of T. castaneum to plant toxicants. These findings may have implications for the development of novel therapeutics to control this agriculturally important pest.

Chemical Ecology, Biochemistry, and Molecular Biology of Insect Hydrocarbons

Insect cuticular hydrocarbons (CHCs) consist of complex mixtures of straight-chain alkanes and alkenes, and methyl-branched hydrocarbons. In addition to restricting water loss through the cuticle and preventing desiccation, they have secondarily evolved to serve a variety of functions in chemical communication and play critical roles as signals mediating the life histories of insects. In this review, we describe the physical properties of CHCs that allow for both waterproofing and signaling functions, summarize their roles as inter- and intraspecific chemical signals, and discuss the influences of diet and environment on CHC profiles. We also present advances in our understanding of hydrocarbon biosynthesis. Hydrocarbons are biosynthesized in oenocytes and transported to the cuticle by lipophorin proteins. Recent work on the synthesis of fatty acids and their ultimate reductive decarbonylation to hydrocarbons has taken advantage of powerful new tools of molecular biology, including genomics and RNA interference knockdown of specific genes, to provide new insights into the biosynthesis of hydrocarbons.

Knockdown of CYP301B1 and CYP6AX1v2 increases the susceptibility of the brown planthopper to beta-asarone, a potential plant-derived insecticide

The cytochrome P450 monooxygenases of insects play crucial roles in the metabolic detoxification of insecticides. Our previous finding showed that two cytochrome P450 genes, both CYP301B1 and CYP6AX1v2, in the BPH underwent overexpression due to β-asarone. In this study, we investigated the molecular characteristics, expression patterns and functions of these two cytochrome P450 genes. The results showed that CYP301B1 had the highest expression level in the eggs, while CYP6AX1v2 was expressed in macropterous female adults. Moreover, the expression level of CYP301B1 in the head was higher than that in the integument, fat body and gut. The expression level of CYP6AX1v2 in the fat body and gut was higher than that in head and integument. Importantly, silencing CYP301B1 and CYP6AX1v2 separately could increase the sensitivity, resulting in significant higher mortality of BPH following treatment with β-asarone. Our findings indicated that CYP301B1 and CYP6AX1v2 could contribute to the resistance of BPH to β-asarone, and these two genes may be involved in the detoxification metabolism of β-asarone in BPH.

Diversity and evolution of the P450 family in arthropods

The P450 family (CYP genes) of arthropods encodes diverse enzymes involved in the metabolism of foreign compounds and in essential endocrine or ecophysiological functions. The P450 sequences (CYPome) from 40 arthropod species were manually curated, including 31 complete CYPomes, and a maximum likelihood phylogeny of nearly 3000 sequences is presented. Arthropod CYPomes are assembled from members of six CYP clans of variable size, the CYP2, CYP3, CYP4 and mitochondrial clans, as well as the CYP20 and CYP16 clans that are not found in Neoptera. CYPome sizes vary from two dozen genes in some parasitic species to over 200 in species as diverse as collembolans or ticks. CYPomes are comprised of few CYP families with many genes and many CYP families with few genes, and this distribution is the result of dynamic birth and death processes. Lineage-specific expansions or blooms are found throughout the phylogeny and often result in genomic clusters that appear to form a reservoir of catalytic diversity maintained as heritable units. Among the many P450s with physiological functions, six CYP families are involved in ecdysteroid metabolism. However, five so-called Halloween genes are not universally represented and do not constitute the unique pathway of ecdysteroid biosynthesis. The diversity of arthropod CYPomes has only partially been uncovered to date and many P450s with physiological functions regulating the synthesis and degradation of endogenous signal molecules (including ecdysteroids) and semiochemicals (including pheromones and defense chemicals) remain to be discovered. Sequence diversity of arthropod P450s is extreme, and P450 sequences lacking the universally conserved Cys ligand to the heme have evolved several times. A better understanding of P450 evolution is needed to discern the relative contributions of stochastic processes and adaptive processes in shaping the size and diversity of CYPomes.

Both LmCYP4G genes function in decreasing cuticular penetration of insecticides in Locusta migratoria

BACKGROUND

Cuticular hydrocarbons (CHCs) have a critical role in preventing desiccation and penetration of xenobiotics in insects. Previous studies have shown that cytochrome P450 subfamily 4G (CYP4G) enzymes are oxidative decarbonylases, essential for CHC biosynthesis. However, it is unclear whether there are functional differences between the two CYP4G genes in most insects. In Locusta migratoria, we identified two CYP4G genes (LmCYP4G62 and LmCYP4G102). LmCYP4G102 plays a critical role in the synthesis of CHCs, but the function of LmCYP4G62 is unknown.

RESULTS

We identified, characterized, and compared two LmCYP4G genes, based on L. migratoria transcriptomic and genomic databases. RT-qPCR showed that both were highly expressed in tissues with which oenocytes are associated, the integument and fat body. Immunostaining indicated that LmCYP4G62 and LmCYP4G102 were highly abundant in oenocytes in these tissues. However, the two enzymes had a different subcellular distribution, with LmCYP4G62 localized on the plasma membrane and LmCYP4G102 dispersed throughout the oenocyte cytoplasm, presumably on the endoplasmic reticulum. RNA interference-mediated gene silencing against each of the two genes resulted in reduced CHC contents, in all classes for LmCYP4G102, but mostly shorter chain CHCs for LmCYP4G62. Silencing of both genes resulted in increased insecticide penetration through the cuticle, and increased locust susceptibility to desiccation and insecticides.

CONCLUSION

Our studies suggest that both LmCYP4G62 and LmCYP4G102 contribute to hydrocarbon biosynthesis and play key roles in protecting locusts from water loss and insecticide penetration, but they are not fully redundant. Further, the two LmCYP4G genes might be used as new targets for insect pest management. © 2020 Society of Chemical Industry.

Deciphering the role of Rhodnius prolixus CYP4G genes in straight and methyl-branched hydrocarbon formation and in desiccation tolerance

Insect cuticle hydrocarbons are involved primarily in waterproofing the cuticle, but also participate in chemical communication and regulate the penetration of insecticides and microorganisms. The last step in insect hydrocarbon biosynthesis is carried out by an insect-specific cytochrome P450 of the 4G subfamily (CYP4G). Two genes (CYP4G106 and CYP4G107) have been reported in the triatomines Rhodnius prolixus and Triatoma infestans. In this work, their molecular and functional characterization is carried out in R. prolixus, and their relevance to insect survival is assessed. Both genes are expressed almost exclusively in the integument and have an expression pattern dependent on the developmental stage and feeding status. CYP4G106 silencing diminished significantly the straight-chain hydrocarbon production while a significant reduction - mostly of methyl-branched chain hydrocarbons - was observed after CYP4G107 silencing. Molecular docking analyses using different aldehydes as hydrocarbon precursors predicted a better fit of straight-chain aldehydes with CYP4G106 and methyl-branched aldehydes with CYP4G107. Survival bioassays exposing the silenced insects to desiccation stress showed that CYP4G107 is determinant for the waterproofing properties of the R. prolixus cuticle. This is the first report on the in vivo specificity of two CYP4Gs to make mostly straight or methyl-branched hydrocarbons, and also on their differential contribution to insect desiccation.

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

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

Brown marmorated stink bug, Halyomorpha halys (Stål), genome: putative underpinnings of polyphagy, insecticide resistance potential and biology of a top worldwide pest

BACKGROUND

Halyomorpha halys (Stål), the brown marmorated stink bug, is a highly invasive insect species due in part to its exceptionally high levels of polyphagy. This species is also a nuisance due to overwintering in human-made structures. It has caused significant agricultural losses in recent years along the Atlantic seaboard of North America and in continental Europe. Genomic resources will assist with determining the molecular basis for this species' feeding and habitat traits, defining potential targets for pest management strategies.

RESULTS

Analysis of the 1.15-Gb draft genome assembly has identified a wide variety of genetic elements underpinning the biological characteristics of this formidable pest species, encompassing the roles of sensory functions, digestion, immunity, detoxification and development, all of which likely support H. halys' capacity for invasiveness. Many of the genes identified herein have potential for biomolecular pesticide applications.

CONCLUSIONS

Availability of the H. halys genome sequence will be useful for the development of environmentally friendly biomolecular pesticides to be applied in concert with more traditional, synthetic chemical-based controls.