Odorant degrading carboxylesterases modulate foraging and mating behaviors of Grapholita molesta

Plant Tannase: Evolutionary and Functional Divergence Features

In plants, α/β-hydrolase regulates the hydrolysis of ester compounds, enriching the types and functions of specialized metabolites. In this study, three genes─CsCSE, CsCXE3, and CsTA─which encode caffeoyl shikimate esterase (CSE), carboxylesterase (CXE), and tannase (TA), respectively, were isolated from the tea plant genome through multiomics correlation analysis. Evolutionary analysis showed that CSE and CXE were ancient, whereas TA emerged in core eudicots approximately 120 million years ago. Enzyme activity assays revealed that CsCSE and CsCXE3 catalyze phenolic acid and acetate ester hydrolysis, respectively. Interestingly, CsTA not only has the catalytic function of CsCSE and CsCXE3 but also catalyzes the hydrolysis of galloylated catechin, hydrolyzable tannin, and hormone ester. Overall, CsTA is a newly derived α/β-hydrolase with evolutionary and functional divergence features. This study expands our understanding of the physiological significance of plant TA and provides insights into the potential role of CsTA in the complex metabolic processes of tea plants.

Dissecting the role of pheromone-binding protein 2 in courtship behavior of male Grapholita molesta moths

For fruit-boring pests like Grapholita molesta, the courtship behavior of male moths is a crucial aspect that can be utilized for developing control methods. This study investigates the role of pheromone-binding proteins (PBPs) in the courtship behavior of male G. molesta moths, particularly how sex pheromone components affect PBP expression. We found that three GmolPBPs genes were mainly expressed in the antennae of adult males, with no expression in larvae or pupae. Notably, GmolPBP2 expression was significantly higher in males, while GmolPBP1 was more pronounced in females. Unmated males exposed to females or the sex pheromone component Z8-12:Ac showed marked upregulation of GmolPBPs expression. Using affinity chromatography, we purified GmolPBPs and confirmed their binding affinities. Especially for GmolPBP2, this protein had a high affinity for Z8-12:Ac and E8-12:Ac. RNA interference targeting GmolPBPs revealed that silencing GmolPBP2 significantly reduced male responses to sex pheromone components and courtship behavior towards females, while silencing GmolPBP1 and GmolPBP3 had no significant effects. These findings highlight the crucial role of GmolPBP2 in mediating male courtship behavior, emphasizing the importance of PBPs in pheromone communication and mating success in G. molesta.

Hierarchical architecture of neo-sex chromosomes and accelerated adaptive evolution in tortricid moths

Sex chromosomes can expand through fusion with autosomes, thereby acquiring unique evolutionary patterns. In butterflies and moths (Lepidoptera), these sex chromosome-autosome (SA) fusions occur relatively frequently, suggesting possible evolutionary advantages. Here, we investigated how SA fusion affects chromosome features and molecular evolution in leafroller moths (Lepidoptera: Tortricidae). Phylogenomic analysis showed that Tortricidae diverged ∼124 million years ago, accompanied by an SA fusion between the Merian elements M(20 + 17) and MZ. In contrast to partial autosomal fusions, the fused neo-Z Chromosome developed a hierarchical architecture, in which the three elements exhibit heterogeneous sequence features and evolutionary patterns. Specifically, the M17 part had a distinct base composition and chromatin domains. Unlike M20 and MZ, M17 was expressed at the same levels as autosomes in both sexes, compensating for the lost gene dosage in females. Concurrently, the SA fusion drove M17 as an evolutionary hotspot, accelerating the evolution of several genes related to ecological adaptation (e.g., ABCCs) and facilitating the divergence of closely related species, whereas the undercompensated M20 did not show such an effect. Thus, accelerated evolution under a novel pattern of dosage compensation may have favored the adaptive radiation of this group. This study demonstrates the association between a karyotype variant and adaptive evolution and explains the recurrent SA fusion in the Lepidoptera.

High Antennal Expression of CYP6K1 and CYP4V2 Participate in the Recognition of Alarm Pheromones by Solenopsis invicta Buren

Insects have highly developed olfactory systems in which cytochrome P450s (CYPs) were involved as odor-degrading enzymes throughout the olfactory recognition of odor compounds by insects to avoid continuous stimulation of signaling molecules and thus damage to the olfactory nervous. To understand whether the highly expressed CYPs in the antennae play an olfactory function in Solenopsis invicta worker, in this study, we find six highly expressed antennal CYPs from the transcriptome of S. invicta. Multiple sequence alignment and phylogenetic analysis divided them into two families: the CYP3 family (SinvCYP6K1, SinvCYP6K1-1) and the CYP4 family (SinvCYP4C1, SinvCYP4C1-1, SinvCYP4C1-2, SinvCYP4V2). The expression patterns of these six CYPs were analyzed by RT-qPCR, which revealed that SinvCYP6K1 and SinvCYP4V2 were only highly expressed in the antennae of adult workers. The expression of SinvCYP6K1 and SinvCYP4V2 in workers was markedly diminished after feeding with dsRNA. The electroantennography (EAG) assay demonstrated that the silencing of either SinvCYP6K1 or SinvCYP4V2 resulted in a notable reduction in the EAG response of workers to 2-ethyl-3,6(5)-dimethylpyrazine (EDMP). Furthermore, the trajectory behavior assay showed that the worker's range and speed of movement in response to EDMP significant decreased after the silencing of SinvCYP6K1 and SinvCYP4V2. The findings indicated that both SinvCYP6K1 and SinvCYP4V2 were implicated in the recognition of EDMP by S. invicta.

Transcriptomic analysis of male diamondback moth antennae: Response to female semiochemicals and allyl isothiocyanate

Female semiochemicals and allyl isothiocyanate (AITC) attract moths, and the moths use odorant-degrading enzymes (ODEs) to break down the excess odor. By identifying antennae-specific ODEs, researchers have established the molecular foundation for odorant degradation and signal inactivation in insects. This enables further exploration of new pest control methods. Currently, the degradation of female semiochemicals and AITC has received limited attention, inspiring this study to identify target ODEs in diamondback moths through transcriptome analysis. Sequencing of antennae from male adults (MA) exposed to female adults (FA) and AITC yielded a substantial 54.18 Gb of clean data, revealing 2276 differentially expressed genes (DEGs) between the MA and MA-FA treatments, and 629 DEGs between MA and MA-AITC treatments. The analysis of MAs exposed to FAs and AITC identified 29 and 17 ODEs, respectively, mainly involving aldehyde dehydrogenases (ALDHs), alcohol dehydrogenases (ADs), cytochrome P450s (CYPs), and UDP-glucuronosyltransferases (UGTs). Pathway analysis revealed primary enrichment in glycolysis/gluconeogenesis and fatty acid degradation in female adult treatments. In contrast, AITC treatments showed major enrichment in pathways related to pentose and glucuronate interconversions, retinol metabolism, and ascorbate and aldarate metabolism. Additionally, qRT-PCR analysis validated the expression patterns of 10 ODE genes in response to these treatments, with varying results observed among the genes. These findings indicate significant changes in ODE expression levels, providing a molecular foundation for identifying potential targets for behavioral inhibitors.

Young Goji Fruit Volatiles Regulate the Oviposition Behavior and Chemosensory Gene Expression of Gravid Female Neoceratitis asiatica

The goji fruit fly, Neoceratitis asiatica, is a major pest on the well-known medicinal plant Lycium barbarum. Dissecting the molecular mechanisms of the oviposition selection of N. asiatica regarding the host plant will help to identify new strategies for pest fly control. However, the molecular mechanism of chemical communication between the goji fruit fly and the host goji remains unclear. Hence, our study found that young goji fruit volatiles induced the oviposition response of gravid female N. asiatica. After N. asiatica was exposed to young goji fruit volatiles, the expression of six chemosensory genes (NasiOBP56h3 and OBP99a1 in the antennae; OBP99a2, OBP99a3 and CSP2 in the legs; and OBP56a in the ovipositor) was significantly upregulated in different organs of female N. asiatica compared with the group without odor treatment according to transcriptome data. Further results of qPCR verification show that the expression levels of the six selected upregulated genes after the flies were exposed to host plant volatiles were mostly consistent with the results of transcriptome data. We concluded that six upregulated genes may be involved in the recognition of young goji fruit volatiles by gravid female N. asiatica. Our study preliminarily identifies young goji fruit volatiles as a key factor in the oviposition behavior of N. asiatica, which will facilitate further studies on the mechanisms of host oviposition selection in N. asiatica.

Trypsin-encoding gene function of efficient star polycation nanomaterial-mediated dsRNA feeding delivery system of Grapholita molesta

BACKGROUND

Grapholita molesta is an important and harmful fruit pest worldwide, with widespread feeding hosts. Trypsin, an indispensable hydrolytic digestive protease in the insect gut, is crucial in digestion, growth and development. We analyzed the characteristics of the trypsin-encoding genes, screened for the optimal dose of RNAi mediated by nanocarriers, and investigated various indices of larval growth and development of G. molesta.

RESULTS

Gut content (GC) and RNase A degraded double-stranded RNA (dsRNA), with a faster degradation rate at higher concentrations. Star polycation (SPc) nanomaterials protected dsGFP from degradation by anion-cation binding and did not migrate through agarose gel. The key conserved motifs of the trypsin-encoding genes were similar, exhibiting high homology with those in other lepidopteran insects. An interference efficiency of ≈70% was achieved with SPc nanomaterial-mediated RNA interference with 0.05 μg dsRNA. The efficiency of continuous interference was stable. Trypsin activity, body weight of 8-day-old larvae, pupal weight and emergence rate were significantly reduced, and the larval stage was significantly prolonged.

CONCLUSION

The investigated trypsin gene is a key target gene in the growth and development of G. molesta. We investigated the efficiency and convenience of feeding SPc nanomaterials in a functional study of insects. Our results provide valuable data for the development of efficient trypsin-targeting pesticides. © 2024 Society of Chemical Industry.

Selection and Validation of Reference Genes for Gene Expression in Bactericera gobica Loginova under Different Insecticide Stresses

Insecticide resistance has long been a problem in crop pest control. Bactericera gobica is a major pest on the well-known medicinal plants Lycium barbarum L. Investigating insecticide resistance mechanisms of B. gobica will help to identify pesticide reduction strategies to control the pest. Gene expression normalization by RT-qPCR requires the selection and validation of appropriate reference genes (RGs). Here, 15 candidate RGs were selected from transcriptome data of B. gobica. Their expression stability was evaluated with five algorithms (Delta Ct, GeNorm, Normfinder, BestKeeper and RefFinder) for sample types differing in response to five insecticide stresses and in four other experimental conditions. Our results indicated that the RGs RPL10 + RPS15 for Imidacloprid and Abamectin; RPL10 + AK for Thiamethoxam; RPL32 + RPL10 for λ-cyhalothrin; RPL10 + RPL8 for Matrine; and EF2 + RPL32 under different insecticide stresses were the most suitable RGs for RT-qPCR normalization. EF1α + RPL8, EF1α + β-actin, β-actin + EF2 and β-actin + RPS15 were the optimal combination of RGs under odor stimulation, temperature, developmental stages and both sexes, respectively. Overall, EF2 and RPL8 were the two most stable RGs in all conditions, while α-TUB and RPL32 were the least stable RGs. The corresponding suitable RGs and one unstable RG were used to normalize a target cytochrome P450 CYP6a1 gene between adult and nymph stages and under imidacloprid stress. The results of CYP6a1 expression were consistent with transcriptome data. This study is the first research on the most stable RG selection in B. gobica nymphs exposed to different insecticides, which will contribute to further research on insecticide resistance mechanisms in B. gobica.

The Odorant-Binding Protein 1 Mediates the Foraging Behavior of Grapholita molesta Larvae

Since eggs are laid directly on fruit skin, it is typically believed that food odor has little impact on the foraging of Grapholita molesta larvae. It is crucial to note that larvae that hatch on twigs and leaves could need some sort of identification system when foraging. Here, 22 GmolOBP genes were identified from the G. molesta larval transcriptome via the comparison of conserved domain and homology in the protein level. GmolOBP1 had strong affinities for important pear-fruit volatiles, which caused larvae strong behavioral responses. However, after GmolOBP1 silencing, the larvae lost their attraction to methyl salicylate, α-farnesene, butyl acetate, ethyl butanoate, and ethyl hexanoate, and the effects of larvae seeking various pears were significantly reduced. Consequently, GmolOBP1 was required for the reception of pear volatiles and was involved in mediating how G. molesta larvae foraged. Our research revealed the GmolOBP1 foraging signal recognition mechanism as well as potential molecular targets for field pest management.

Roles of insect odorant binding proteins in communication and xenobiotic adaptation

Odorant binding proteins (OBPs) are small water-soluble proteins mainly associated with olfaction, facilitating the transport of odorant molecules to their relevant receptors in the sensillum lymph. While traditionally considered essential for olfaction, recent research has revealed that OBPs are engaged in a diverse range of physiological functions in modulating chemical communication and defense. Over the past 10 years, emerging evidence suggests that OBPs play vital roles in purifying the perireceptor space from unwanted xenobiotics including plant volatiles and pesticides, potentially facilitating xenobiotic adaptation, such as host location, adaptation, and pesticide resistance. This multifunctionality can be attributed, in part, to their structural variability and effectiveness in transporting, sequestering, and concealing numerous hydrophobic molecules. Here, we firstly overviewed the classification and structural properties of OBPs in diverse insect orders. Subsequently, we discussed the myriad of functional roles of insect OBPs in communication and their adaptation to xenobiotics. By synthesizing the current knowledge in this field, our review paper contributes to a comprehensive understanding of the significance of insect OBPs in chemical ecology, xenobiotic adaptation, paving the way for future research in this fascinating area of study.

Antennae-enriched expression of candidate odorant degrading enzyme genes in the turnip aphid, Lipaphis erysimi

Aphids heavily rely on their olfactory system for foraging behavior. Odorant-degrading enzymes (ODEs) are essential in preserving the olfactory acuity of aphids by removing redundant odorants in the antennae. Certain enzymes within this group stand out as being enriched and/or biased expressed in the antennae, such as carboxylesterases (CXEs), cytochrome P450 (CYPs), glutathione S-transferases (GSTs), and UDP-glycosyltransferases (UGTs). Here, we performed a comparative transcriptome analysis of antennae and body tissue to isolate the antennal ODE genes of turnip aphid Lipaphis erysimi. A dataset of one CXE, seven CYPs, two GSTs, and five UGTs enriched in the antennae was identified and subjected to sequence analysis. Furthermore, qRT-PCR analyses showed that 13 ODE genes (LeCXE6, LeCYP4c1, LeCYP6a2, LeCYP6a13, LeCYP6a14.2, LeCYP6k1, LeCYP18a1, LeGST1, LeUGT1-7, LeUGT2B7, LeUGT2B13, LeUGT2C1.1, and LeUGT2C1.2) were specifically or significantly elevated in antennal tissues. Among these antennae-enriched ODEs, LeCYP4c1, LeCYP6a2, LeCYP6a13, LeCYP6a14.2, LeCYP18a1, LeUGT2B7, and LeUGT2B13 were found to exhibit significantly higher expression levels in alate aphids compared to apterous and nymph aphids, suggesting their putative role in detecting new host plant location. The results presented in this study highlight the identification and expression of ODE genes in L. erysimi, paving the path to investigate their functional role in odorant degradation during the olfactory processes.

Molecular identification of carboxylesterase genes and their potential roles in the insecticides susceptibility of Grapholita molesta

Grapholita molesta is one of the most damaging pests worldwide in stone and pome fruits. Application of chemical pesticides is still the main method to control this pest, which results in resistance to several types of insecticides. Carboxylesterase (CarE) is one of the important enzymes involved in the detoxification metabolism and tolerance of xenobiotics and insecticides. However, the roles of CarEs in insecticides susceptibility of G. molesta are still unclear. In the present study, the enzyme activity of CarEs and the mRNA expression of six CarE genes were consistently elevated after treatment with three insecticides (emamectin benzoate, lambda-cyhalothrin, and chlorantraniliprole). According to spatio-temporal expression profiles, six CarE genes expressed differently in different developmental stages, and highly expressed in some detoxification metabolic organs. RNAi-mediated knockdown of these six CarE genes indicated that the susceptibility of G. molesta to all these three insecticides were obviously raised after GmCarE9, GmCarE14, GmCarE16, and GmCarE22 knockdown, respectively. Overall, these results demonstrated that GmCarE9, GmCarE14, GmCarE16, and GmCarE22 play a role in the susceptibility of G. molesta to emamectin benzoate, lambda-cyhalothrin, and chlorantraniliprole treatment. This study expands our understanding of CarEs in insects, that the same CarE gene could participate in the susceptibility to different insecticides.

Two Antenna-Enriched Carboxylesterases Mediate Olfactory Responses and Degradation of Ester Volatiles in the German Cockroach Blattella germanica

Insects have evolved an extremely sensitive olfactory system that is essential for a series of physiological and behavioral activities. Some carboxylesterases (CCEs) comprise a major subfamily of odorant-degrading enzymes (ODEs) playing a crucial role in odorant signal inactivation to maintain the odorant receptor sensitivity. In this study, 93 CCEs were annotated in the genome of the German cockroach Blattella germanica, a serious urban pest. Phylogenetic and digital tissue expression pattern analyses identified two antenna-enriched CCEs, BgerCCE021e3 and BgerCCE021d1, as candidate ODEs. RNA interference (RNAi)-mediated knockdown of BgerCCE021e3 and BgerCCE021d1 resulted in partial anosmia with experimental insects exhibiting reduced attraction to ester volatile resources and slower olfactory responses than controls. Furthermore, enzymatic conversion of geranyl acetate by crude male antennal extracts from BgerCCE021e3 and BgerCCE021d1 RNAi insects was also significantly reduced. Our results provide evidence for CCE function in German cockroach olfaction and provide a basis for further exploring behavioral inhibitors that target olfactory-related CCEs.

Dynamic Roles of Insect Carboxyl/Cholinesterases in Chemical Adaptation

Insects have evolved several intricate defense mechanisms to adapt to their chemical environment. Due to their versatile capabilities in hydrolytic biotransformation, insect carboxyl/cholinesterases (CCEs) play vital roles in the development of pesticide resistance, facilitating the adaptation of insects to their host plants, and manipulating insect behaviors through the olfaction system. CCEs confer insecticide resistance through the mechanisms of qualitative or quantitative changes of CCE-mediated enhanced metabolism or target-site insensitivity, and may contribute to the host plant adaptation. CCEs represent the first odorant-degrading enzymes (ODEs) discovered to degrade insect pheromones and plant odors and remain the most promising ODE candidates. Here, we summarize insect CCE classification, currently characterized insect CCE protein structure characteristics, and the dynamic roles of insect CCEs in chemical adaptation.

Multiple Receptors Contribute to the Attractive Response of Caenorhabditis elegans to Pathogenic Bacteria

Nematodes feed mainly on bacteria and sense volatile signals through their chemosensory system to distinguish food from pathogens. Although nematodes recognizing bacteria by volatile metabolites are ubiquitous, little is known of the associated molecular mechanism. Here, we show that the antinematode bacterium Paenibacillus polymyxa KM2501-1 exhibits an attractive effect on Caenorhabditis elegans via volatile metabolites, of which furfural acetone (FAc) acts as a broad-spectrum nematode attractant. We show that the attractive response toward FAc requires both the G-protein-coupled receptors STR-2 in AWC neurons and SRA-13 in AWA and AWC neurons. In the downstream olfactory signaling cascades, both the transient receptor potential vanilloid channel and the cyclic nucleotide-gated channel are necessary for FAc sensation. These results indicate that multiple receptors and subsequent signaling cascades contribute to the attractive response of C. elegans to FAc, and FAc is the first reported ligand of SRA-13. Our current work discovers that P. polymyxa KM2501-1 exhibits an attractive effect on nematodes by secreting volatile metabolites, especially FAc and 2-heptanone, broadening our understanding of the interactions between bacterial pathogens and nematodes. IMPORTANCE Nematodes feed on nontoxic bacteria as a food resource and avoid toxic bacteria; they distinguish them through their volatile metabolites. However, the mechanism of how nematodes recognize bacteria by volatile metabolites is not fully understood. Here, the antinematode bacterium Paenibacillus polymyxa KM2501-1 is found to exhibit an attractive effect on Caenorhabditis elegans via volatile metabolites, including FAc. We further reveal that the attractive response of C. elegans toward FAc requires multiple G-protein-coupled receptors and downstream olfactory signaling cascades in AWA and AWC neurons. This study highlights the important role of volatile metabolites in the interaction between nematodes and bacteria and confirms that multiple G-protein-coupled receptors on different olfactory neurons of C. elegans can jointly sense bacterial volatile signals.

Antennal transcriptomic analysis of carboxylesterases and glutathione S-transferases associated with odorant degradation in the tea gray geometrid, Ectropis grisescens (Lepidoptera, Geometridae)

Introduction: Carboxylesterases (CXEs) and glutathione S-transferases (GSTs) can terminate olfactory signals during chemosensation by rapid degradation of odorants in the vicinity of receptors. The tea grey geometrid, Ectropis grisescens (Lepidoptera, Geometridae), one of the most devastating insect herbivores of tea plants in China, relies heavily on plant volatiles to locate the host plants as well as the oviposition sites. However, CXEs and GSTs involved in signal termination and odorant clearance in E. grisescens remains unknown. Methods: In this study, identification and spatial expression profiles of CXEs and GSTs in this major tea pest were investigated by transcriptomics and qRT-PCR, respectively. Results: As a result, we identified 28 CXEs and 16 GSTs from female and male antennal transcriptomes. Phylogenetic analyses clustered these candidates into several clades, among which antennal CXEs, mitochondrial and cytosolic CXEs, and delta group GSTs contained genes commonly associated with odorants degradation. Spatial expression profiles showed that most CXEs (26) were expressed in antennae. In comparison, putative GSTs exhibited a diverse expression pattern across different tissues, with one GST expressed specifically in the male antennae. Disscussion: These combined results suggest that 12 CXEs (EgriCXE1, 2, 4, 6, 8, 18, 20-22, 24, 26, and 29) and 5 GSTs (EgriGST1 and EgriGST delta group) provide a major source of candidate genes for odorants degradation in E. grisescens.

Transcriptome-Based Selection and Validation of Reference Genes for Gene Expression in Goji Fruit Fly (Neoceratitis asiatica Becker) under Developmental Stages and Five Abiotic Stresses

Goji fruit fly, Neoceratitis asiatica, is a major pest on the well-known medicinal plant Lycium barbarum. Dissecting molecular mechanisms of infestation and host selection of N. asiatica will contribute to the determination of best management practices for pest fly control. Gene expression normalization by Real-time quantitative PCR (qPCR) requires the selection and validation of appropriate reference genes (RGs). Hence, 15 candidate RGs were selected from transcriptome data of N. asiatica. Their expression stability was evaluated with five algorithms (∆Ct, Normfinder, GeNorm, BestKeeper, and RefFinder) for sample types differing in the developmental stage, sex, tissue type, and in response to five different abiotic stresses. Our results indicated that the RGs β-Actin + GST for sex, RPL32 + EF1α for tissue type, RPS13+ EF1α for developmental stages along with odor stimulation, color induction, and starvation-refeeding stresses, EF1α + GAPDH under insecticide stress, RPS13 + RPS18 under temperature stress, respectively, were selected as the most suitable RGs for qPCR normalization. Overall, RPS18 and EF1α were the two most stable RGs in all conditions, while RPS15 and EF1β were the least stable RGs. The corresponding suitable RGs and one unstable RG were used to normalize a target odorant-binding protein OBP56a gene in male and female antennae, different tissues, and under odor stimulation. The results of OBP56a expression were consistent with transcriptome data. Our study is the first research on the most stable RGs selection in N. asiatica, which will facilitate further studies on the mechanisms of host selection and insecticide resistance in N. asiatica.

Transcriptomic Identification and Expression Profile Analysis of Odorant-Degrading Enzymes from the Asian Corn Borer Moth, Ostrinia furnacalis

The Asian corn borer moth Ostrinia furnacalis is an important lepidopteran pest of maize in Asia. Odorant-degrading enzymes (ODEs), including carboxylesterases (CCEs), glutathione S-transferases (GSTs), cytochrome P450s (CYPs), UDP-glycosyltransferases (UGTs), and aldehyde oxidases (AOXs), are responsible for rapid inactivation of odorant signals in the insect antennae. In this study, we performed a transcriptome assembly for the antennae of O. furnacalis to identify putative ODE genes. Transcriptome sequencing revealed 35,056 unigenes, and 21,012 (59.94%) of these were annotated by searching against the reference sequences in the NCBI non-redundant (NR) protein database. For functional classification, these unigenes were subjected to Gene Ontology (GO), Eukaryotic Orthologous Groups (KOG), and Kyoto Encyclopedia of Genes and Genomes (KEGG) annotations. We identified 79 genes encoding putative ODEs: 19 CCEs, 17 GSTs, 24 CYPs, 13 UGTs, and 6 AOXs. BLASTX best hit results indicated that these genes shared quite high amino acid identities with their respective orthologs from other lepidopteran species. Reverse transcription-quantitative PCR showed that OfurCCE2, OfurCCE5, and OfurCCE18 were enriched in male antennae, while OfurCCE7 and OfurCCE10 were enriched in female antennae. OfurCCE14 and OfurCCE15 were expressed at near-equal amounts in the antennae of both sexes. Our findings establish a solid foundation for future studies aimed at understanding the olfactory functions of these genes in O. furnacalis.

RNA Sequencing Reveals the Potential Adaptation Mechanism to Different Hosts of Grapholita molesta

Grapholita molesta is an important fruit tree worldwide pest which feeds on hosts extensively and does serious harm. In this paper, the growth and development parameters and protease activities of G. molesta fed on different hosts were compared. Using Illumina RNA sequencing technology, 18 midgut samples from five different hosts (apple, pear, plum, peach and peach shoots) and artificial diet were sequenced and compared with the reference genome, resulting in 15269 genes and 2785 predicted new genes. From 15 comparative combinations, DEGs were found from 286 to 4187 in each group, with up-regulated genes from 107 to 2395 and down-regulated genes from 83 to 2665. KEGG pathway analysis showed that DEGs were associated with amino acid metabolism, starch and sucrose metabolism, carbohydrate metabolism, and hydrolase activity. A total of 31 co-expression gene modules of different hosts were identified by WGCNA. qRT-PCR showed that the expression pattern of the trypsin gene was consistent with RNA sequencing. In this study, growth and development parameters, protease activity, DEGs, enrichment analysis and qRT-PCR were combined to reveal the adaptation process to different hosts of G. molesta in many aspects. The results of this study provide a basis for further exploration of the molecular mechanism of host adaptation of G. molesta.

Antennae-abundant expression of candidate cytochrome P450 genes associated with odorant degradation in the asian citrus psyllid, Diaphorina citri

The Asian citrus psyllid, Diaphorina citri, is a notorious pest that is an efficient vector for Candidatus Liberibacter asiaticus (CLas), the causal agent of citrus huanglongbing (HLB). The olfactory system of insects is crucial for foraging and mating behavior. Antennae-abundant odorant degrading enzymes (ODEs), including cytochrome P450 (CYPs), are important in degrading redundant odorant molecules to recover the insect olfactory. In this study, to isolate the antennal CYP genes of D. citri, we generated four transcriptomes from female/male antennae and body through deep sequencing of RNA libraries. Seven DcCYP genes preferentially expressed in antennae were first identified by comparing the antennal and body transcriptomes. Phylogenetic analysis grouped four DcCYPs (DcCYP6a13, DcCYP6j1, DcCYP6k1, and DcCYP6a2) into the CYP3 class, whereas DcCYP4d2, DcCYP4c62, and DcCYP4d8 were clustered in the CYP4 clade. qRT-PCR analyses across developmental stages and tissues showed they were antennae-abundant in both genders and constantly expressed from the first instar nymph to the adult. The results presented here highlight the isolation and expression of CYP genes in D. citri antennae, providing valuable insights into their putative role in odorant degradation.

Genome-Wide Identification of Aldehyde Oxidase Genes in Moths and Butterflies Suggests New Insights Into Their Function as Odorant-Degrading Enzymes

Aldehyde oxidases (AOXs) are common detoxifying enzymes in several organisms. In insects, AOXs act in xenobiotic metabolism and as odorant-degrading enzymes (ODEs). These last appear as crucial enzymes in the life cycle of insects, helping to reset their olfactory system, particularly in lepidopterans, which fulfill important ecological roles (e.g., pollination or destructive life cycles). A comprehensive understanding of their olfactory system has provided opportunities to study key chemosensory proteins. However, no significant advance has been made around lepidopteran AOXs research, and even less around butterflies, a recently evolved lineage. In this study we have identified novel AOX gene families in moths and butterflies in order to understand their role as ODEs. Eighteen genomes from both moths and butterflies were used for phylogenetics, molecular evolution and sequence analyses. We identified 164 AOXs, from which 91 are new. Their phylogeny showed two main clades that are potentially related to odorant-degrading function, where both moths and butterflies have AOXs. A first ODE-related clade seems to have a non-ditrysian origin, likely related to plant volatiles. A second ODE-related clade could be more pheromone-biased. Molecular evolution analysis suggests a slight purifying selection process, though a number of sites appeared under positive selection. ODE-related AOXs have changed a phenylalanine residue by proline in the active site. Finally, this study could serve as a reference for further evolutionary and functional studies around Lepidopteran AOXs.

Binding Properties of Odorant-Binding Protein 4 of Tirathaba rufivena to Areca catechu Volatiles

Odorant-binding proteins (OBPs) play a key role in the olfactory system and are essential for mating and oviposition host selection. Tirathaba rufivena, a serious lepidopterous insect pest of the palm area in recent years, has threatened cultivations of Areca catechu in Hainan. Female-biased odorant-binding protein 4 of T. rufivena (TrufOBP4) expression was hypothesized to participate in the process of oviposition host recognition and localization. In this study, we cloned and analyzed the cDNA sequence of TrufOBP4. The predicted mature protein TrufOBP4 is a small, soluble, secretory protein and belongs to a classic OBP subfamily. Fluorescence binding assay results showed that TrufOBP4 had high binding abilities with the host plant volatiles, octyl methoxycinnamate, dibutyl phthalate, myristic acid and palmitic acid. These four components tend to dock in the same binding pocket based on the molecular docking result. The interactions and contributions of key amino acid residues were also characterized. This research provides evidence that TrufOBP4 might participate in the chemoreception of volatile compounds from inflorescences of A. catechu and can contribute to the integrated management of T. rufivena.

Host-pathogen interaction between Asian citrus psyllid and entomopathogenic fungus (Cordyceps fumosorosea) is regulated by modulations in gene expression, enzymatic activity and HLB-bacterial population of the host

The host-pathogen interaction has been explored by several investigations, but the impact of fungal pathogens against insect resistance is still ambiguous. Therefore, we assessed the enzymatic activity and defense-related gene expression of Asian citrus psyllid (ACP) nymphal and adult populations on Huanglongbing-diseased citrus plants under the attack of Cordyceps fumosorosea. Overall, five enzymes viz. superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), glutathione S-transferase (GST), carboxylesterase (CarE), and four genes, namely SOD, 16S, CYP4C68, CYP4BD1, were selected for respective observations from ACP populations. Enzymatic activity of four enzymes (SOD, POD, GST, CarE) was significantly decreased after 5-days post-treatment (dpt) and 3-dpt fungal exposure in fungal treated ACP adult and nymphal populations, respectively, whereas the activity of CAT was boosted substantially post-treatment time schedule. Besides, we recorded drastic fluctuations in the expression of CYP4 genes among fungal treated ACP populations. After 24 hours post-treatment (hpt), expression of both CYP4 genes was boosted in fungal treated populations than controlled populations (adult and nymph). After 3-dpt, however, the expression of CYP4 genes was declined in the given populations. Likewise, fungal attack deteriorated the resistance of adult and nymphal of ACP population, as SOD expression was down-regulated in fungal-treated adult and nymphs after 5-dpt and 3-dpt exposure, respectively. Moreover, bacterial expression via the 16S gene was significantly increased in fungal-treated adult and nymphal ACP populations with increasing post-treatment time. Overall, our data illustrate that the fungal application disrupted the insect defense system. The expression of these genes and enzymes suppress the immune function of adult and nymphal ACP populations. As it is reported first time that the applications of C. fumosorosea against ACP reduce insect resistance by interfering with the CYP4 and SOD system. Therefore, we propose new strategies to discover the role of certain toxic compounds from fungus, which can reduce insect resistance, focusing on resistance-related genes and enzymes.