Effect of Silencing CYP6B6 of Helicoverpa armigera (Lepidoptera: Noctuidae) on Its Growth, Development, and Insecticide Tolerance

Physiological and Molecular Mechanisms of Lepidopteran Insects: Genomic Insights and Applications of Genome Editing for Future Research

Lepidopteran insects are a major threat to global agriculture, causing significant crop losses and economic damage. Traditional pest control methods are becoming less effective due to the rapid evolution of insecticide resistance. This study explores the current status and genomic characteristics of 1315 Lepidopteran records, alongside an overview of relevant research, utilizing advanced functional genomics techniques, including RNA-seq and CRISPR/Cas9 gene-editing technologies to uncover the molecular mechanisms underlying insecticide resistance. Our genomic analysis revealed significant variability in genome size, assembly quality, and chromosome number, which may influence species' biology and resistance mechanisms. We identified key resistance-associated genes and pathways, including detoxification and metabolic pathways, which help these insects evade chemical control. By employing CRISPR/Cas9 gene-editing techniques, we directly manipulated resistance-associated genes to confirm their roles in resistance, demonstrating their potential for targeted interventions in pest management. These findings emphasize the value of integrating genomic data into the development of effective and sustainable pest control strategies, reducing reliance on chemical insecticides and promoting environmentally friendly integrated pest management (IPM) approaches. Our study highlights the critical role of functional genomics in IPM and its potential to provide long-term solutions to the growing challenge of Lepidopteran resistance.

Comparative transcriptome profiling of two pesticides, Acephate and Chlorantraniliprole in non-targeted insect model, Drosophila melanogaster

Acephate and chlorantraniliprole are two insecticides widely used in agricultural applications. Several studies were focused on the mode of action and related biological and cellular level expressions. However, the sub-lethal dose and related molecular expression level of acephate and chlorantraniliprole have not been evaluated or studied to the same degree. In this study, we investigated the sub-lethal toxicity of acephate and chlorantraniliprole in Drosophila melanogaster. The EC50 value was recorded with high difference, and is found to be 1.9 μg/ml and 0.029 μg/ml respectively for acephate and chlorantraniliprole, the difference is simply because of the different modes of action. The 1/5th EC50 concentration was selected for studying the pesticide induced transcriptomics in D. melanogaster. Both pesticides significantly altered the expression profile of several transcripts which are involved in proteolysis, detoxification, chromosome associated proteins and immune response genes and so on. The effect of both pesticides on D. melanogaster was further explored by screening the genes involved in toxicity, which were analyzed using, GO and KEGG pathways. The results revealed that the sub-lethal exposure of both pesticides caused significant changes in the global gene transcription profiles and each pesticide had their unique mode of alteration in the D. melanogaster.

Functional characterization of Helicoverpa assulta CYP6B6 in insecticide metabolism

The oriental tobacco budworm Helicoverpa assulta (Lepidoptera: Noctuidae) is a specialist pest that may cause serious damages to important crops such as chili pepper and tobacco. Various man-made insecticides have been applied to control the infestation of this pest. To understand how this pest copes with insecticides, it is required to identify key players involved in insecticide transformation. In this study, a P450 gene of CYP6B subfamily was identified in the oriental tobacco budworm, and its expression pattern was revealed. Moreover, the activities of HassCYP6B6 against 12 insecticides were explored using recombinant enzymes produced in the facile Escherichia coli. Data from metabolic experiments showed that HassCYP6B6 was able to metabolize conventional insecticides including organophosporates (diazinon, malathion, phoxim), carbamate propoxur, and pyrethroid esfenvalerate, while no significant metabolism was observed towards new-type pesticides such as neonicotinoids (acetamiprid, imidacloprid), diamides (chlorantraniliprole, cyantraniliprole), macrocyclic lactone (emamectin benzoate, ivermectin), and metaflumizone. Structures of metabolites were proposed based on mass spectrometry analyses. The results demonstrate that HassCYP6B6 plays important roles in the transformation of multiple insecticides via substrate-dependent catalytic mechanisms including dehydrogenation, hydroxylation and oxidative desulfurization. The findings have important applied implications for the usage of insecticides.

Chromosome-level genome assembly of Dastarcus helophoroides provides insights into CYP450 genes expression upon insecticide exposure

BACKGROUND

Dastarcus helophoroides is an important natural enemy of cerambycids, and is wildly used in biological control of pests. Nevertheless, the absence of complete genomic information limits the investigation of the underlying molecular mechanisms. Here, a chromosome-level of Dastarcus helophoroides genome is assembled using a combination strategy of Illumina, PacBio, 10x™ Genomics, and Hi-C.

RESULTS

The final assembly is 609.09 Mb with contig N50, scaffold N50 and GC content of 5.46 Mb, 42.56 Mb and 31.50%, respectively, and 95.25% of the contigs anchor into 13 chromosomes. In total 14 890 protein-coding genes and 65.37% repeat sequences are predicted in the assembly genome. The phylogenetic analysis of single-copy gene families shared among 20 insect species indicates that Dastarcus helophoroides is placed as the sister species to clade (Nitidulidae+Curculionoidea+Chrysomeloidea) + Tenebrionoidea, and diverges from the related species ~242.9 Mya. In total 36 expanded gene families are identified in Dastarcus helophoroides genome, and are functionally related to drug metabolism and metabolism of xenobiotics by cytochrome P450. Some members of CYP4 Clade and CYP6 Clade are up-regulated in Dastarcus helophoroides adults upon insecticide exposure, of which expressions of DhCYP4Q, DhCYP6A14X1 and DhCYP4C1 are significantly up-regulated. The silencing of the three genes leads to adults more sensitive to insecticide and increased knocked-down rate, which may indicate their critical roles in stress resistance and detoxication.

CONCLUSION

Our study systematically integrated the chromosome-level genome, transcriptome and gene expression of Dastarcus helophoroides, which will provide valuable resources for understanding mechanisms of pesticide metabolism, growth and development, and utilization of the natural enemy in integrated control. © 2022 Society of Chemical Industry.

Effects of transgenic cotton lines expressing dsAgCYP6CY3-P1 on the growth and detoxification ability of Aphis gossypii glover

BACKGROUND

The pest Aphis gossypii Glover globally causes considerable economic losses on various crops by its feeding damage and disease transmission. Transgenic plants that produce double-stranded RNA (dsRNA) targeted to insect genes are being developed as a pest control strategy. In this study, we evaluated the effects of transgenic cotton-mediated RNA interference (RNAi) on the growth and detoxification ability of A. gossypii after the transgenic cotton lines expressing dsAgCYP6CY3-P1 (the TG cotton lines) were obtained on the basis of exploring the functions of CYP6CY3 in our previous research.

RESULTS

The developmental time of third- and fourth-instar nymphs which fed on the TG cotton lines were significantly prolonged. Life table parameters showed that the fitness of cotton aphids from the TG cotton lines decreased. Additionally, the relative expression level of CYP6CY3 in cotton aphids which fed on the TG cotton lines was significantly reduced by 47.3 % at 48 h compared with that from the nontransgenic cotton (the NT cotton). Bioassay showed that silencing of CYP6CY3 increased mortality of the nymphs to imidacloprid by 28.49 % (at 24 h) and to acetamiprid by 73.77 % (at 48 h), respectively.

CONCLUSION

These results indicated that the TG cotton lines delayed the growth and development of A. gossypii, but also decreased population density and increased its sensitivity to imidacloprid and acetamiprid, respectively. The results provide further support for the development and application of plant-mediated RNAi. © 2022 Society of Chemical Industry.

Two P450 genes, CYP6SN3 and CYP306A1, involved in the growth and development of Chilo suppressalis and the lethal effect caused by vetiver grass

Chilo suppressalis is a widely distributed pest occurring in nearly all paddy fields, which has developed high level resistance to different classes of insecticides. Vetiver grass has been identified as a dead-end trap plant for the alternative control of C. suppressalis. In this study, two cytochrome P450 monooxygenase (P450) genes, CsCYP6SN3 and CsCYP306A1, were identified and characterized, which are expressed at all developmental stages, with the highest expression in the midguts and fat bodies of 3rd instar larvae. Vetiver significantly inhibited the expression levels of CsCYP6SN3 and CsCYP306A1 in 3rd larvae after feeding. RNA interference showed that silencing CsCYP6SN3 and CsCYP306A1 genes dramatically reduced the pupation rate and pupa weight. Feeding on vetiver after silencing CsCYP6SN3 and CsCYP306A1 led to higher mortality compared with feeding on rice. In conclusion, these findings indicated that the expression levels of CsCYP6SN3 and CsCYP306A1 were associated with the lethal effect of vetiver against C. suppressalis larvae and functional knowledge about these two detoxification genes could provide new targets for agricultural pest control.

Biodegradation of Free Gossypol by Helicoverpa armigera Carboxylesterase Expressed in Pichia pastoris

Gossypol is a polyphenolic toxic secondary metabolite derived from cotton. Free gossypol in cotton meal is remarkably harmful to animals. Furthermore, microbial degradation of gossypol produces metabolites that reduce feed quality. We adopted an enzymatic method to degrade free gossypol safely and effectively. We cloned the gene cce001a encoding carboxylesterase (CarE) into pPICZαA and transformed it into Pichia pastoris GS115. The target protein was successfully obtained, and CarE CCE001a could effectively degrade free gossypol with a degradation rate of 89%. When esterase was added, the exposed toxic groups of gossypol reacted with different amino acids and amines to form bound gossypol, generating substances with (M + H) m/z ratios of 560.15, 600.25, and 713.46. The molecular formula was C₂₇H₂₈O₁₃, C₃₄H₃₆N₂O₆, and C₄₇H₅₉N₃O₃. The observed instability of the hydroxyl groups caused the substitution and shedding of the group, forming a substance with m/z of 488.26 and molecular formula C₃₁H₃₆O₅. These properties render the CarE CCE001a a valid candidate for the detoxification of cotton meal. Furthermore, the findings help elucidate the degradation process of gossypol in vitro.

Down-Regulation of P450 Genes Enhances Susceptibility to Indoxacarb and Alters Physiology and Development of Fall Armyworm, Spodoptera frugipreda (Lepidoptera: Noctuidae)

The fall armyworm (FAW), Spodoptera frugiperda (J.E. Smith), is a pest of many important crops globally. Effective control is challenging, with the pest exhibiting resistance to different synthetic pesticides across various groups. However, the mechanisms employed by resistant insects for overexpression of relevant detoxification genes remain unclear. The activity of detoxification enzymes was investigated in this study. Additionally, using RNA interference (RNAi), a functional analysis was completed of two P450s genes in an indoxacarb resistant population of fall armyworms. Elevated resistance levels (resistance ratio = 31.37-fold) in indoxacarb-selected populations of FAW were observed after 14 generations. The qRT-PCR showed higher expression of two cytochrome P450 genes, CYP321A7 and CYP6AE43, in this selected population compared to the control population. RNAi was applied to knock down the P450 dsCYP321A7 and dsCYP6AE43 genes in the FAW larvae. Droplet feeding of the dsRNAs (CYP321A7 and CYP6AE43) via an artificial diet significantly increased mortality rates in the indoxacarb treated population. A shorter larval developmental time of FAW was detected in all dsRNAs-fed larvae. Correspondingly, larval mass was reduced by dsRNAs in indoxacarb resistant populations of fall armyworm. Larval feeding assays demonstrate that dsRNAs targeting, specifically of CYP321A7 and CYP6AE43 enzymes, could be a beneficial technique in the management of indoxacarb resistant populations. Further study on the potential use of dsRNA and its application should be conducted in efforts to counter the development of resistance in FAW against various insecticides in the field.

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

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

Integration of transcriptome and proteome reveals molecular mechanisms underlying stress responses of the cutworm, Spodoptera litura, exposed to different levels of lead (Pb)

Heavy metals are major environmental pollutants that affect organisms across different trophic levels. Herbivorous insects play an important role in the bioaccumulation, and eventually, biomagnification of these metals. Although effects of heavy metal stress on insects have been well-studied, the molecular mechanisms underlying their effects remain poorly understood. Here, we used the RNA-Seq profiling and isobaric tags for relative and absolute quantitation (iTRAQ) approaches to unravel these mechanisms in the polyphagous pest Spodoptera litura exposed to lead (Pb) at two different concentrations (12.5 and 100 mg Pb/kg; PbL and PbH, respectively). Altogether, 1392 and 1630 differentially expressed genes (DEGs) and 58, 114 differentially expressed proteins (DEPs) were identified in larvae exposed to PbL and PbH, respectively. After exposed to PbL, the main up-regulated genes clusters and proteins in S. litura larvae were associated with their metabolic processes, including carbohydrate, protein, and lipid metabolism, but the levels of cytochrome P450 associated with the pathway of xenobiotic biodegradation and metabolism were found to be decreased. In contrast, the main up-regulated genes clusters and proteins in larvae exposed to PbH were enriched in the metabolism of xenobiotic by cytochrome P450, drug metabolism-cytochrome P450, and other drug metabolism enzymes, while the down-regulated genes and proteins were found to be closely related to the lipid (lipase) and protein (serine protease, trypsin) metabolism and growth processes (cuticular protein). These findings indicate that S. litura larvae exposed to PbL could enhance food digestion and absorption to prioritize for growth rather than detoxification, whereas S. litura larvae exposed to PbH reduced food digestion and absorption and channelized the limited energy for detoxification rather than growth. These contrasting results explain the dose-dependent effects of heavy metal stress on insect life-history traits, wherein low levels of heavy metal stress induce stimulation, while high levels of heavy metal stress cause inhibition at the transcriptome and proteome levels.

Effect of RNAi targeting CYP6CY3 on the growth, development and insecticide susceptibility of Aphis gossypii by using nanocarrier-based transdermal dsRNA delivery system

RNA interference (RNAi) has been proved to be a viable method for agricultural pest control. Due to the limited uptake of dsRNA in hemiptera insects, this study used nanocarrier SPc (star polycation) transdermal delivery systems to deliver two truncated fragments (P1/P2) dsRNA of the CYP6CY3 for silencing this target gene in Aphis gossypii. After the cotton aphid was sprayed with the SPc + dsP1/P2 mixture, the expression level of target gene in SPc + dsP1 treatment group was not different from that in dsP1 group at 24 h, 48 h, and significantly lower than that in dsP1 group at 60 h, 72 h, respectively; and the expression level of target gene in SPc + dsP2 treatment group was not different from that in dsP2 group at 24 h, and significantly lower than that in dsP2 group from 48 h, 60 h, 72 h, respectively. In addition, the expression level was continuously silenced after spraying the SPc + dsP1/P2 mixture and significant reduced by 79.7% and 84.3% at 48 h compared with the H₂O control group, the mortality rate reached 48.09% and 43.18% at 84 h, respectively. And the cumulative reproduction number of cotton aphids also decreased, but the cumulative death number of newborn nymphs had an increase trend, compared with the control groups. Bioassays after RNAi showed that the silencing of CYP6CY3 increased the susceptibility of the 4^th instar aphid to imidacloprid, and increased mortality by 67.21% and 58.69% at 96 h, respectively. The life table parameters of the offspring from the 4^th instar cotton aphids from the SPc + dsP1/P2 treatment groups showed that the offspring had a longer pre-reproductive period and post-reproductive period. The intrinsic growth rate was 0.231 ± 0.005, 0.210 ± 0.013 and the finite growth rate was 1.260 ± 0.007 and 1.234 ± 0.016 in the SPc + dsP1/P2 treatment group, these two parameters of the two groups were lower than that of the corresponding control，the population doubling time of the two groups was prolonged and the developmental duration was delayed. These results indicate that CYP6CY3 plays a key role in the growth, development, reproduction and detoxification ability in cotton aphids, and may be as a potential RNAi target for controlling aphids, laying the foundation for the development of new environmentally-friendly RNA pesticides in this field.

Alcohol dehydrogenase 5 of Helicoverpa armigera interacts with the CYP6B6 promoter in response to 2-tridecanone

Alcohol dehydrogenase 5 (ADH5) is a member of medium-chain dehydrogenase/reductase family and takes part in cellular formaldehyde and S-nitrosoglutathione metabolic network. 2-tridecanone (2-TD) is a toxic compound in many Solanaceae crops to defend against a variety of herbivory insects. In the broader context of insect development and pest control strategies, this study investigates how a new ADH5 from Helicoverpa armigera (HaADH5) regulates the expression of CYP6B6, a gene involved in molting and metamorphosis, in response to 2-TD treatment. Cloning of the HaADH5 complementary DNA sequence revealed that its 1002 bp open reading frame encodes 334 amino acids with a predicted molecular weight of 36.5 kD. HaADH5 protein was purified in the Escherichia coli Transetta (pET32a-HaADH5) strain using a prokaryotic expression system. The ability of HaADH5 protein to interact with the 2-TD responsive region within the promoter of CYP6B6 was confirmed by an in vitro electrophoretic mobility shift assay and transcription activity validation in yeast. Finally, the expression levels of both HaADH5 and CYP6B6 were found to be significantly decreased in the midgut of 6th instar larvae after 48 h of treatment with 10 mg/g 2-TD artificial diet. These results indicate that upon 2-TD treatment of cotton bollworm, HaADH5 regulates the expression of CYP6B6 by interacting with its promoter. As HaADH5 regulation of CYP6B6 expression may contribute to the larval xenobiotic detoxification, molting and metamorphosis, HaADH5 is a candidate target for controlling the growth and development of cotton bollworm.

Suppressing tawny crazy ant (Nylanderia fulva) by RNAi technology

The tawny crazy ant (Nylanderia fulva) is a new invasive pest in the United States. At present, its management mainly relies on the use of synthetic insecticides, which are generally ineffective at producing lasting control of the pest, necessitating alternative environmentally friendly measures. In this study, we evaluated the feasibility of gene silencing to control this ant species. Six housekeeping genes encoding actin (NfActin), coatomer subunit β (NfCOPβ), arginine kinase (NfArgK), and V-type proton ATPase subunits A (NfvATPaseA), B (NfvATPaseB) and E (NfvATPaseE) were cloned. Phylogenetic analysis revealed high sequence similarity to homologs from other ant species, particularly the Florida carpenter ant (Camponotus floridanus). To silence these genes, vector L4440 was used to generate six specific RNAi constructs for bacterial expression. Heat-inactivated, dsRNA-expressing Escherichia coli were incorporated into artificial diet. Worker ants exhibited reduced endogenous gene expression after feeding on such diet for 9 d. However, only ingestion of dsRNAs of NfCOPβ (a gene involved in protein trafficking) and NfArgK (a cellular energy reserve regulatory gene in invertebrates) caused modest but significantly higher ant mortality than the control. These results suggest that bacterially expressed dsRNA can be orally delivered to ant cells as a mean to target its vulnerabilities. Improved efficacy is necessary for the RNAi-based approach to be useful in tawny crazy ant management.

RNA interference-mediated knockdown of a cytochrome P450 gene enhanced the toxicity of α-cypermethrin in xanthotoxin-fed larvae of Spodoptera exigua (Hübner)

The beet armyworm (Spodoptera exigua) is a highly polyphagous agricultural pest that is distributed worldwide. However, the adaptive mechanisms of S. exigua for various insecticides and defensive substances in host plants are unknown. Insect P450 monooxygenases play an important role in the detoxification of plant toxins and insecticides, leading to insecticides resistance. We investigated the induced effects of xanthotoxin exposure on detoxification enzyme activity and larval tolerance to α-cypermethrin in S. exigua. Our results showed that the lethal concentration (LC₅₀) of α-cypermethrin for xanthotoxin-exposed larvae was 2.1-fold higher than in the control. Moreover, cytochrome P450 enzyme activity was significantly elevated by upregulation of P450 genes in treated larvae. RT-qPCR results showed that CYP9A10 expression level was significantly increased in all treatments, while maximal expression level was observed in xanthotoxin+α-cypermethrin-fed larvae. RNAi-mediated silencing of CYP9A10 further increased mortality by 18%, 26% and 35% at 48 h and by 27%, 43% and 55% at 72 h when larvae were exposed to diets containing chemicals as compared to the control. The results show that CYP9A10 might play an important role in xanthotoxin and α-cypermethrin detoxification in S. exigua. RNAi-mediated silencing could provide an effective synergistic agent for pest control or insecticide resistance management.

CYP6B6 is involved in esfenvalerate detoxification in the polyphagous lepidopteran pest, Helicoverpa armigera

The cotton bollworm, Helicoverpa armigera, is a polyphagous pest that has a strong capacity to evolve resistance against various classes of insecticides. Cytochrome P450 enzymes have been suspected involved in pyrethroid metabolism and resistance in this pest. However, how many and which P450s are involved in pyrethroid metabolism is largely unknown. In this study, CYP6B6 and NADPH-cytochrome P450 reductase (HaCPR) from H. armigera were successfully co-expressed in Escherichia coli. Incubation of esfenvalerate with the recombinant CYP6B6-HaCPR monooxygenase complex revealed that CYP6B6 was able to transform esfenvalerate into 4'-hydroxy fenvalerate. Kcat and Km values for the formation of 4'-hydroxyfenvalerate by the E. coli-produced CYP6B6 were determined to be 1.65±0.11min^-1 and 4.10±0.84μM respectively. Our results demonstrate that CYP6B6 has the ability to hydroxylate esfenvalerate, thus plays a role in fenvalerate detoxification.