Chemosensory Proteins Research Articles

Minus-C subfamily has diverged from Classic odorant-binding proteins in honeybees

Odorant-binding proteins (OBPs) in insects bind to volatile chemical cues that are important in regulating insect behavior. It is hypothesized that OBPs bind with specificity to certain volatiles and may help in transport and delivery to odorant receptors (ORs), and may help in buffering the olfactory response and aid the insect in various behaviors. Honeybees are eusocial insects that perceive olfactory cues and strongly rely on them to perform complex olfactory behaviors. Here, we have identified and annotated odorant-binding proteins and few chemosensory proteins from the genome of the dwarf honey bee, Apis florea, using an exhaustive homology-based bioinformatic pipeline and analyzed the evolutionary relationships between the OBP subfamilies. Our study confirms that the Minus-C subfamily in honey bees has diverged from the Classic subfamily of odorant-binding proteins.

Genome-wide identification and transcriptome-based expression pattern of chemosensory genes in two wild silkmoths,Antheraea pernyi andAntheraea yamamai

Antheraea pernyi Guérin-Méneville andAntheraea yamamai Guérin-Méneville are two closely related wild silkmoths belonging to the family Saturniidae with highly edible and silk-producing value. In this study, we characterised candidate chemosensory genes from the genomes of the two silkmoths. InA. pernyi, 38 odorant-binding proteins (OBPs), 21 chemosensory proteins (CSPs), 3 sensory neuron membrane proteins (SNMPs), 28 ionotropic receptors (IRs), 54 odorant receptors (ORs) and 53 gustatory receptors (GRs) were identified. InA. yamamai, 36 OBPs, 21 CSPs, 3 SNMPs, 30 IRs, 50 ORs and 54 GRs were identified. Phylogenetic analysis showed that the OBP, OR and GR genes were significantly expanded or contracted in the two silkmoths when compared to lepidopteran modelBombyx mori L., while the CSP genes were only expanded. The SNMP and IR genes were greatly conserved in the two silkmoths andB. mori. Most OBP, CSP, SNMP, IR and OR genes had the expression in the antennal transcriptome, but most GR genes showed no expression. This is the first study to characterise chemosensory genes of Saturniidae species in the genome and antennal transcriptome.

Identification and expression analyses of the olfactory-related genes in different tissues' transcriptome of a predacious soldier beetle, Podabrus annulatus (Coleoptera, Cantharidae).

We sequenced and analyzed the transcriptomes from different tissues of the soldier beetle, Podabrus annulatus (Coleoptera: Cantharidae), and obtained 75.74 Gb clean reads which were assembled into 95,274 unigenes. Among these transcripts, 25,484 unigenes of highly quality were annotated. Based on annotation and tBLASTn results, we identified a total of 101 candidate olfactory-related genes for the first time, including 11 putative odorant-binding proteins (OBPs), 6 chemosensory proteins (CSP), 50 olfactory receptors (ORs), 25 gustatory receptors (GRs), 6 ionotropic receptors (IRs), and 3 sensory neuron membrane proteins (SNMPs). BLASTX best-hit results indicated that these chemosensory genes were most identical to their respective orthologs from Photinus pyralis. Phylogenetic analyses also revealed that the ORs, GRs, and IRs of Podabrus annulatus are closely related to those of Photinus pyralis. The fragment per kilobase per million mapped fragments (FPKM) values showed that the PannOBP2, PannOBP3, and PannOBP10 were predominantly expressed in the antennae, PannOBP1 in the abdomen-thorax, while others were not identified to be tissue-specific. These olfactory-related differentially expressed genes (DEGs) demonstrated different roles in the olfactory system of Podabrus annulatus. This study establishes the groundwork for future research into the molecular mechanism of olfactory recognition in Podabrus annulatus.

Functional characterization of chemosensory proteins in response to artificial light treatment in Thalassodes immissaria.

Chemosensory proteins (CSPs) play a vital role in the response to environmental stimuli in insects. However, the involvement of insect CSPs in the stress response to night-time environmental changes has not been examined. In the current study, four TiCSP genes were first cloned from Thalassodes immissaria by transcriptome and RACE-PCR techniques. TiCSPs had typical characteristics of insect CSPs, including a highly conserved four-cysteine motif and olfactory-specific protein D (OS-D) or OS-D superfamily domains. TiCSP1-4 were clustered classified within different clades in a phylogenetic analysis and were differentially expressed at all developmental stages. Under night-time artificial light stress, the expression levels of TiCSP1 in males were significantly decreased at 24 h, and those of TiCSP2 were decreased in both adult sexes at 48 h. In a molecular docking analysis, TiCSPs showed relatively higher binding affinities with sex pheromone components than with host plant volatile molecules. Taking the reduced expression levels of TiCSPs and binding affinities into account, TiCSP1 and TiCSP2 are involved in the stress response processes of T.immissaria under light treatment. Our study supplies basic data for the evaluation of the effects of light interference control technology - an emerging physical control measure on nontarget pests of lychee orchards. © 2023 Society of Chemical Industry.

Conserved orthology in termite chemosensory gene families

Termites are eusocial insects known to use a variety of pheromones in tasks necessary for maintenance of their societies. As such, olfaction and pheromone communication in termites has been an object of intense study; trail-following pheromones (TFPs) and sex-pairing pheromones (SPPs), for example, have been identified in many termite species. In contrast, the molecular basis of olfactory detection is understudied in the group. Here, we present chemosensory genes of three species of termites belonging to three distinct lineages, Neotermes cubanus (Kalotermitidae), Prorhinotermes simplex (Rhinotermitidae), and Inquilinitermes inquilinus (Termitidae). Using antennal transcriptome screening of termite workers, we identified the chemosensory genes, which allowed us to perform phylogenetic analysis. We found a comparatively large repertoires of odorant receptors (ORs), gustatory receptors (GRs), ionotropic receptors (IRs), odorant binding proteins (OBPs), chemosensory proteins (CSPs), and sensory neuron membrane proteins (SNMPs). The evolutionary analysis of termite chemosensory genes revealed Isoptera-specific expansions with a 1:1 orthologous pattern, indicating the existence of conserved olfactory functions. Our findings on basal eusocial insects will further enhance our understanding of the molecular underpinnings of eusociality and the evolution of olfactory communication in termites.

The Cellular Abundance of Chemoreceptors, Chemosensory Signaling Proteins, Sensor Histidine Kinases, and Solute Binding Proteins of Pseudomonas aeruginosa Provides Insight into Sensory Preferences and Signaling Mechanisms.

Chemosensory pathways and two-component systems are important bacterial signal transduction systems. In the human pathogen Pseudomonas aeruginosa, these systems control many virulence traits. Previous studies showed that inorganic phosphate (Pi) deficiency induces virulence. We report here the abundance of chemosensory and two-component signaling proteins of P. aeruginosa grown in Pi deficient and sufficient media. The cellular abundance of chemoreceptors differed greatly, since a 2400-fold difference between the most and least abundant receptors was observed. For many chemoreceptors, their amount varied with the growth condition. The amount of chemoreceptors did not correlate with the magnitude of chemotaxis to their cognate chemoeffectors. Of the four chemosensory pathways, proteins of the Che chemotaxis pathway were most abundant and showed little variation in different growth conditions. The abundance of chemoreceptors and solute binding proteins indicates a sensing preference for amino acids and polyamines. There was an excess of response regulators over sensor histidine kinases in two-component systems. In contrast, ratios of the response regulators CheY and CheB to the histidine kinase CheA of the Che pathway were all below 1, indicative of different signaling mechanisms. This study will serve as a reference for exploring sensing preferences and signaling mechanisms of other bacteria.

Evidence for the Participation of Chemosensory Proteins in Response to Insecticide Challenge in Conopomorpha sinensis

Chemosensory proteins (CSPs) are a type of efficient transporters that can bind various hydrophobic compounds. Previous research has shown that the expression levels of some insect CSPs were significantly increased after insecticide treatment. However, the role of CSPs in response to insecticide challenge is unclear. Conopomorpha sinensis is the most destructive borer pest of litchi (Litchi chinensis) and longan (Euphoria longan) in the Asia-Pacific region. Here, we studied the expression patterns and potential functions of 12 CSP genes (CsCSPs) from C. sinensis in response to λ-cyhalothrin exposure. The spatiotemporal distribution of CsCSPs suggested that they were predominantly expressed in the female abdomen, female legs, and male legs. The expression levels of CsCSPs were affected in a time-dependent manner after λ-cyhalothrin treatment in both sexes of C. sinensis adults. Compared to the control group, the expression levels of CsCSP1, CsCSP2, CsCSP9, and CsCSP12 in females were significantly increased by 2-4 times, while only one CsCSP, three CsCSPs, and two CsCSPs were significantly upregulated in males at three time points post-treatment. The sex-biased variance of CSP expression may be related to sex-specific detoxification enzymatic activities and survival rates of C. sinensis in response to insecticide challenge. Homology modeling and molecular docking analyses showed that the binding energy value of CsCSP1-12 to λ-cyhalothrin was negative and the binding energy between CsCSP9 and λ-cyhalothrin was the lowest (-11.35 kJ/mol). Combined with expression alterations of CsCSP1-12, the results indicate that CsCSP1, CsCSP2, CsCSP9, and CsCSP12 were involved in binding and ferrying of λ-cyhalothrin in C. sinensis.

Involvement of three chemosensory proteins in perception of host plant volatiles in the tea green leafhopper, Empoasca onukii.

Chemosensory proteins (CSPs) can bind and transport odorant molecules, which are believed to be involved in insect chemoreception. Here, we investigated three CSPs in perception of volatiles in Empoasca onukii. Expression profiles showed that although EonuCSP4, EonuCSP 6-1 and EonuCSP6-2 were ubiquitously expressed in heads, legs, thoraxes and abdomen, they were all highly expressed in the antennae of E. onukii. Further, fluorescence competitive binding assays revealed that EonuCSP4 and 6-1 had binding affinities for three plant volatiles, suggesting their possible involvement in the chemosensory process. Among them, EonuCSP6-1 showed relatively high binding affinities for benzaldehyde. Behavioral assays revealed that the adults of E. onukii showed a significant preference for two compounds including benzaldehyde. The predicted three-dimensional (3D) structures of these 3 CSP have the typical six α-helices, which form the hydrophobic ligand-binding pocket. We therefore suggest that Eoun6-1 might be involved in the chemoreception of the host-related volatiles for E. onukii. Our data may provide a chance of finding a suitable antagonist of alternative control strategies which block the perception of chemosensory signals in pest, preventing the food- orientation behaviors.

The antennal transcriptome of Triatoma infestans reveals substantial expression changes triggered by a blood meal

BackgroundTriatoma infestans is the main vector of Chagas disease in the Americas, currently transmitting it in Argentina, Paraguay, and Bolivia. Many T. infestans populations present insecticide resistance, reducing the efficiency of control campaigns. Alternative vector control methods are needed, and molecular targets mediating fundamental physiological processes can be a promising option to manipulate kissing bug behavior. Therefore, it is necessary to characterize the main sensory targets, as well as to determine whether they are modulated by physiological factors. In order to identify gene candidates potentially mediating host cue detection, the antennal transcripts of T. infestans fifth instar larvae were sequenced and assembled. Besides, we evaluated whether a blood meal had an effect on transcriptional profiles, as responsiveness to host-emitted sensory cues depends on bug starvation.ResultsThe sensory-related gene families of T. infestans were annotated (127 odorant receptors, 38 ionotropic receptors, 11 gustatory receptors, 41 odorant binding proteins, and 25 chemosensory proteins, among others) and compared to those of several other hemipterans, including four triatomine species. Several triatomine-specific lineages representing sensory adaptations developed through the evolution of these blood-feeding heteropterans were identified. As well, we report here various conserved sensory gene orthogroups shared by heteropterans. The absence of the thermosensor pyrexia, of pickpocket receptor subfamilies IV and VII, together with clearly expanded takeout repertoires, are revealed features of the molecular bases of heteropteran antennal physiology. Finally, out of 2,122 genes whose antennal expression was significantly altered by the ingestion of a blood meal, a set of 41 T. infestans sensory-related genes (9 up-regulated; 32 down-regulated) was detected.ConclusionsWe propose that the set of genes presenting nutritionally-triggered modulation on their expression represent candidates to mediate triatomine host-seeking behavior. Besides, the triatomine-specific gene lineages found represent molecular adaptations to their risky natural history that involves stealing blood from an enormously diverse set of vertebrates. Heteropteran gene orthogroups identified may represent unknown features of the sensory specificities of this largest group of hemipteroids. Our work is the first molecular characterization of the peripheral modulation of sensory processes in a non-dipteran vector of human disease.

Transcriptome analysis and identification of chemosensory genes in the larvae of Plagiodera versicolora

BackgroundIn insects, the chemosensory system is crucial in guiding their behaviors for survival. Plagiodera versicolora (Coleoptera: Chrysomelidae), is a worldwide leaf-eating forest pest in salicaceous trees. There is little known about the chemosensory genes in P. versicolora. Here, we conducted a transcriptome analysis of larvae heads in P. versicolora.ResultsIn this study, 29 odorant binding proteins (OBPs), 6 chemosensory proteins (CSPs), 14 odorant receptors (ORs), 13 gustatory receptors (GRs), 8 ionotropic receptors (IRs) and 4 sensory neuron membrane proteins (SNMPs) were identified by transcriptome analysis. Compared to the previous antennae and foreleg transcriptome data in adults, 12 OBPs, 2 CSPs, 5 ORs, 4 IRs, and 7 GRs were newly identified in the larvae. Phylogenetic analyses were conducted and found a new candidate CO2 receptor (PverGR18) and a new sugar receptor (PverGR23) in the tree of GRs. Subsequently, the dynamic expression profiles of various genes were analyzed by quantitative real-time PCR. The results showed that PverOBP31, OBP34, OBP35, OBP38, and OBP40 were highly expressed in larvae, PverOBP33 and OBP37 were highly expressed in pupae, and PverCSP13 was highly expressed in eggs, respectively.ConclusionsWe identified a total of 74 putative chemosensory genes based on a transcriptome analysis of larvae heads in P. versicolora. This work provides new information for functional studies on the chemoreception mechanism in P. versicolora.

Olfactory Gene Families in Scopula subpunctaria and Candidates for Type-II Sex Pheromone Detection

Scopula subpunctaria, an abundant pest in tea gardens, produce type-II sex pheromone components, which are critical for its communicative and reproductive abilities; however, genes encoding the proteins involved in the detection of type-II sex pheromone components have rarely been documented in moths. In the present study, we sequenced the transcriptomes of the male and female S. subpunctaria antennae. A total of 150 candidate olfaction genes, comprising 58 odorant receptors (SsubORs), 26 ionotropic receptors (SsubIRs), 24 chemosensory proteins (SsubCSPs), 40 odorant-binding proteins (SsubOBPs), and 2 sensory neuron membrane proteins (SsubSNMPs) were identified in S. subpunctaria. Phylogenetic analysis, qPCR, and mRNA abundance analysis results suggested that SsubOR46 may be the Orco (non-traditional odorant receptor, a subfamily of ORs) of S. subpunctaria. SsubOR9, SsubOR53, and SsubOR55 belonged to the pheromone receptor (PR) clades which have a higher expression in male antennae. Interestingly, SsubOR44 was uniquely expressed in the antennae, with a higher expression in males than in females. SsubOBP25, SsubOBP27, and SsubOBP28 were clustered into the moth pheromone-binding protein (PBP) sub-family, and they were uniquely expressed in the antennae, with a higher expression in males than in females. SsubOBP19, a member of the GOBP2 group, was the most abundant OBP in the antennae. These findings indicate that these olfactory genes, comprising five candidate PRs, three candidate PBPs, and one candidate GOBP2, may be involved in type II sex pheromone detection. As well as these genes, most of the remaining SsubORs, and all of the SsubIRs, showed a considerably higher expression in the female antennae than in the male antennae. Many of these, including SsubOR40, SsubOR42, SsubOR43, and SsubIR26, were more abundant in female antennae. These olfactory and ionotropic receptors may be related to the detection of host plant volatiles. The results of this present study provide a basis for exploring the olfaction mechanisms in S. subpunctaria, with a focus on the genes involved in type II sex pheromones. The evolutionary analyses in our study provide new insights into the differentiation and evolution of lepidopteran PRs.

Sensing of a spore surface protein by a Drosophila chemosensory protein induces behavioral defense against fungal parasitic infections

In addition to innate immunity in a physiological context, insects have evolved behavioral defenses against parasite attacks. Here, we report that Drosophila can sense the CFEM (common in fungal extracellular membrane) protein Mcdc9, which acts as a negative virulence factor of the entomopathogenic fungus Metarhizium robertsii. The individual deletions of 18 CFEM genes in Metarhizium followed by fly infection identified three null mutants that could kill the flies more quickly than the wild-type strain, among which Mcdc9 can coat fungal spores and interact with the fly chemosensory protein CheA75a. The deletion of Mcdc9 in the fungus or the knockdown of CheA75a in flies had a similar effect, in which a greater number of fungal spores were left on flies than on the respective controls after topical infection. Thus, similar to the accelerated death of the wild-type flies treated with ΔMcdc9, the CheA75aRNAi flies succumbed more quickly than the control insects topically challenged with the wild-type strain. The CheA75a gene is highly transcribed in fly legs and wings, and positive electrophysiological responses were evidenced in tarsal sensilla after stimulation with the Mcdc9 protein. The results imply that this CFEM protein could be sensed as a contact elicitor inducing the hygienic behavior of flies against fungal parasitic infection, which reveals a previously unsuspected mechanism of fungus-insect interactions.

Comparison and Functional Analysis of Odorant-Binding Proteins and Chemosensory Proteins in Two Closely Related Thrips Species, Frankliniella occidentalis and Frankliniella intonsa (Thysanoptera: Thripidae) Based on Antennal Transcriptome Analysis.

Two closely related thrips species, Frankliniella occidentalis and Frankliniella intonsa, are important pests on agricultural and horticultural crops. They have several similarities, including occurrence patterns, host range, and aggregation pheromone compounds. However, there are very few reports about the chemosensory genes and olfactory mechanisms in these two species. To expand our knowledge of the thrips chemosensory system, we conducted antennal transcriptome analysis of two thrips species, and identified seven odorant-binding proteins (OBPs) and eight chemosensory proteins (CSPs) in F. occidentalis, as well as six OBPs and six CSPs in F. intonsa. OBPs and CSPs showed high sequence identity between the two thrips species. The RT-qPCR results showed that the orthologous genes FoccOBP1/3/4/5/6, FintOBP1/3/4/6, FoccCSP1/2/3, and FintCSP1/2 were highly expressed in male adults. Molecular docking results suggested that orthologous pairs FoccOBP4/FintOBP4, FoccOBP6/FintOBP6, and FoccCSP2/FintCSP2 might be involved in transporting the major aggregation pheromone compound neryl (S)-2-methylbutanoate, while orthologous pairs FoccOBP6/FintOBP6, FoccCSP2/FintCSP2, and FoccCSP3/FintCSP3 might be involved in transporting the minor aggregation pheromone compound (R)-lavandulyl acetate. These results will provide a fundamental basis for understanding the molecular mechanisms of pheromone reception in the two thrips species.

Identification and Expression Analysis of Odorant-Binding and Chemosensory Protein Genes in Virus Vector Nephotettix cincticeps.

The insect odorant binding proteins (OBPs) and chemosensory proteins (CSPs) are involved in the perception and discrimination of insects to host odor cues. Nephotettix cincticeps, one of the destructive pests of rice plants, not only directly damages hosts by sucking, but also indirectly transmits plant viruses in the field. Previous study found that two rice volatiles ((E)-β-caryophyllene and 2-heptanol) induced by rice dwarf virus (RDV) mediated the olfactory behavior of N. cincticeps, which may promote virus dispersal. However, the OBPs and CSPs in N. cincticeps are still unknown. In this study, to identify the OBP and CSP genes in N. cincticeps, transcriptomic analyses were performed. In total, 46,623 unigenes were obtained. Twenty putative OBP and 13 CSP genes were discovered and identified. Phylogenetic analyses revealed that five putative OBPs belonged to the plus-C OBP family, and the other classic OBPs and CSPs were distributed among other orthologous groups. A total of 12 OBP and 10 CSP genes were detected, and nine OBP and three CSP genes were highly expressed in N. cincticeps antennae compared with other tissues. This study, for the first time, provides a valuable resource to well understand the molecular mechanism of N. cincticeps in the perception and discrimination of the two volatiles induced by RDV infection.

Chemosensory-Related Genes in Marine Copepods.

Living organisms deeply rely on the acquisition of chemical signals in any aspect of their life, from searching for food, mating and defending themselves from stressors. Copepods, the most abundant and ubiquitous metazoans on Earth, possess diversified and highly specified chemoreceptive structures along their body. The detection of chemical stimuli activates specific pathways, although this process has so far been analyzed only on a relatively limited number of species. Here, in silico mining of 18 publicly available transcriptomes is performed to delve into the copepod chemosensory genes, improving current knowledge on the diversity of this multigene family and on possible physiological mechanisms involved in the detection and analysis of chemical cues. Our study identifies the presence of ionotropic receptors, chemosensory proteins and gustatory receptors in copepods belonging to the Calanoida, Cyclopoida and Harpacticoida orders. We also confirm the absence in these copepods of odorant receptors and odorant-binding proteins agreeing with their insect specificity. Copepods have evolved several mechanisms to survive in the harsh marine environment such as producing proteins to respond to external stimulii. Overall, the results of our study open new possibilities for the use of the chemosensory genes as biomarkers in chemical ecology studies on copepods and possibly also in other marine holozooplankters.

Use of Schinus molle (Anacardiaceae) as a means of biological control against Trialeurodes vaporariorum (Aleyrodidae)

Greenhouse whiteflies, Trialeurodes vaporariorum, are very small sucker-whipper-type pests of the family Aleyrodidae. They cause considerable damage to greenhouse crops in the first order and show resistance to chemical insecticides. In this context, we dedicated this study to the control of this pest through the active ingredients extracted from the leaf and fruit part of the pepper tree, Schinus molle by inhibiting the chemosensory protein responsible mainly for capturing external stimuli in these polyphagous insects. By applying molecular modeling methods, including molecular docking, using software Molegro Virtual Docker version 2012.5.5.0, we tested the bioinsecticide potency of seven inhibitors. The results obtained show that the molecule beta- elemol is the best chemosensory protein inhibitor with a score of –82.6648 Kcal/mol and that it forms strong bonds with the active site amino acids of the protein.

Sex-Biased Expression of Olfaction-Related Genes in the Antennae of Apis cerana (Hymenoptera: Apidae).

The olfactory system is essential for honeybees to adapt to complex and ever-changing environments and maintain cohesiveness. The Eastern honeybee Apis cerana is native to Asia and has a long history of managed beekeeping in China. In this study, we analysed the antennal transcriptomes of A. cerana workers and drones using Illumina sequencing. A total of 5262 differentially expressed genes (DEGs) (fold change > 2) were identified between these two castes, with 2359 upregulated and 2903 downregulated in drones compared with workers. We identified 242 candidate olfaction-related genes, including 15 odourant-binding proteins (OBPs), 5 chemosensory proteins (CSPs), 110 odourant receptors (ORs), 9 gustatory receptors (GRs), 8 ionotropic receptors (IRs), 2 sensory neuron membrane proteins (SNMPs) and 93 putative odourant-degrading enzymes (ODEs). More olfaction-related genes have worker-biased expression than drone-biased expression, with 26 genes being highly expressed in workers’ antennae and only 8 genes being highly expressed in drones’ antennae (FPKM > 30). Using real-time quantitative PCR (RT-qPCR), we verified the reliability of differential genes inferred by transcriptomics and compared the expression profiles of 6 ORs (AcOR10, AcOR11, AcOR13, AcOR18, AcOR79 and AcOR170) between workers and drones. These ORs were expressed at significantly higher levels in the antennae than in other tissues (p < 0.01). There were clear variations in the expression levels of all 6 ORs between differently aged workers and drones. The relative expression levels of AcOR10, AcOR11, AcOR13, AcOR18 and AcOR79 reached a high peak in 15-day-old drones. These results will contribute to future research on the olfaction mechanism of A. cerana and will help to better reveal the odourant reception variations between different biological castes of honeybees.

Chemosensory protein 4 is required for Bradysia odoriphaga to be olfactory attracted to sulfur compounds released from Chinese chives.

Bradysia odoriphaga (Diptera: Sciaridae) is a serious pest of Chinese chives cultivated in China. Chemosensory proteins (CSPs) are important components of insect olfactory systems that capture and bind environmental semiochemicals which are then transported to olfactory receptors. Despite their importance, the mechanism of olfaction and related behavioral processes in B. odoriphaga have not been characterized. Here, we found that BodoCSP4 has an important olfactory function. RT-qPCR indicated that BodoCSP4 expression was highest in the heads (antennae removed) of adult males, followed by the antennae of adult males. Competitive binding assays with 33 ligands indicated that BodoCSP4 binds well with methyl allyl disulfide, diallyl disulfide, and n-heptadecane; the corresponding dissolution constants (Ki) were as high as 5.71, 5.71, and 6.85 μM, respectively. 3D-structural and molecular docking indicated that BodoCSP4 has five α-helices and surrounds the ligand with certain hydrophobic residues including Leu60, Leu63, Leu64, Ala67, Val28, Ile30, Ile33, Leu34, and Val86, suggesting these residues help BodoCSP4 bind to ligands. Silencing of BodoCSP4 significantly decreased the attraction of B. odoriphaga males to diallyl disulfide and n-heptadecane but not to methyl allyl disulfide in Y-tube olfaction assays. These results increase our understanding of how BodoCSP4 contributes to host and female localization by B. odoriphaga males.

Transcriptome analysis of megalurothrips usitatus (Bagnall) identifies olfactory genes with ligands binding characteristics of MusiOBP1 and MusiCSP1.

The olfactory system is an important component of insect behavior and is vital for survival and reproduction. However, the genomic characterization and molecular basis of the olfactory response of Megalurothrips usitatus remain relatively unknown. RNA sequencing-built developmental transcriptomes of nymphs, pupae, and adult M. usitatus were examined in order to establish the sequence-based background of M. usitatus olfactory responses. A total of 56,669 unigenes were annotated using GO, NR, Pfam, eggNOG, SwissProt, and KEGG. The number of differentially expressed genes between pupae and nymphs, males and nymphs, and females and nymphs were 10,498, 9,235, and 10,964, respectively. One odorant-binding protein (MusiOBP1) and one chemosensory protein (MusiCSP1) were selected from the transcriptome, and their full-length sequences were obtained using RACE PCR. The relative expression of MusiOBP1 was the highest in primordial females, whereas the relative expression of MusiCSP1 was the highest in primordial pupae. The strongest binding ability to the odor-binding protein MusiOBP1 was observed for β-citronellol. 3-Hydroxy-2-methyl-4-pyrone showed the strongest binding affinity to MusiCSP1. Our analysis suggests that MusiOBP1 and MusiCSP1 may play significant roles in mediating M. usitatus host recognition. This research will improve our knowledge of odorant-binding proteins and chemosensory proteins, which will in turn improve our understanding of insect olfactory systems.

Chromosome-level assembly of Culex pipiens molestus and improved reference genome of Culex pipiens pallens (Culicidae, Diptera).

Culex pipiens molestus and Culex pipiens pallens are two distinct bioforms in the Culex pipiens complex that are important vectors of several pathogens and are widely distributed around the world. In the current study, we present a high-quality chromosome-level genome of Cx. pipiens f. molestus and describe the genetic characteristics of this genome. The assembly genome was 559.749 Mb with contig and scaffold N50 values of 200.952 Mb and 0.370 Mb, and more than 94.78% of the assembled bases were located on 3 chromosomes. A total of 19,399 protein-coding genes were predicted. Many gene families were expanded in the genome of Cx. pipiens f. molestus, particularly those of the chemosensory protein (CSP) and gustatory receptor (GR) gene families. In addition, utilizing Hi-C data, we improved the previously assembled draft genome of Cx. pipiens f. pallens, with scaffold N50 of 186.195 Mb and contig N50 of 0.749 Mb, and more than 97.02% of the assembled bases were located on three chromosomes. This reference genome provides a foundation for genome-based investigations of the unique ecological and evolutionary characteristics of Cx. pipiens f. molestus, and the findings in this study will help to elucidate the mechanisms involved in species divergence in the Culex pipiens complex.