Identification of odorant-binding and chemosensory protein genes and the ligand affinity of two of the encoded proteins suggest a complex olfactory perception system in Periplaneta americana

Involvement of Chemosensory Protein CrufCSP3 in Perception of the Host Location in a Parasitic Wasp Cotesia ruficrus

Chemosensory proteins (CSPs) constitute a class of olfactory proteins localized in insect sensory organs that serve a crucial function in decoding external chemical stimuli. This study aims to elucidate the involvement of CrufCSP3 in olfactory perception within the context of Cotesia ruficrus, an indigenous endoparasitoid targeting the invasive pest Spodoptera frugiperda. Through fluorescence-competitive binding assays and site-directed mutagenesis, we pinpointed four amino acids as pivotal residues involved in the interaction between CrufCSP3 and five host-related compounds. Subsequent RNA interference experiments targeting CrufCSP3 unveiled a reduced sensitivity to specific host-related compounds and a decline in the parasitism rate of the FAW larvae. These findings unequivocally indicate the essential role of CrufCSP3 in the chemoreception process of C. ruficrus. Consequently, our study not only sheds light on the functional importance of CSPs in parasitic wasp behavior but also contributes to the development of eco-friendly and efficacious wasp behavior modifiers for effectively mitigating pest population surges.

NpPP2-B10, an F-Box-Nictaba Gene, Promotes Plant Growth and Resistance to Black Shank Disease Incited by Phytophthora nicotianae in Nicotiana tabacum

Black shank, a devastating disease affecting tobacco production worldwide, is caused by Phytophthora nicotianae. However, few genes related to Phytophthora resistance have been reported in tobacco. Here, we identified NpPP2-B10, a gene strongly induced by P. nicotianae race 0, with a conserved F-box motif and Nictaba (tobacco lectin) domain, in the highly resistant tobacco species Nicotiana plumbaginifolia. NpPP2-B10 is a typical F-box-Nictaba gene. When it was transferred into the black shank-susceptible tobacco cultivar 'Honghua Dajinyuan', it was found to promote resistance to black shank disease. NpPP2-B10 was induced by salicylic acid, and some resistance-related genes (NtPR1, NtPR2, NtCHN50, and NtPAL) and resistance-related enzymes (catalase and peroxidase) were significantly upregulated in the overexpression lines after infection with P. nicotianae. Furthermore, we showed that NpPP2-B10 actively regulated the tobacco seed germination rate, growth rate, and plant height. The erythrocyte coagulation test of purified NpPP2-B10 protein showed that NpPP2-B10 had plant lectin activity, and the lectin content in the overexpression lines was significantly higher than that in the WT, which could lead to accelerated growth and improved resistance of tobacco. SKP1 is an adaptor protein of the E3 ubiquitin ligase SKP1, Cullin, F-box (SCF) complex. We demonstrated that NpPP2-B10 could interact with the NpSKP1-1A gene in vivo and in vitro through yeast two-hybrid (Y2H) and bimolecular fluorescence complementation (BiFC), indicating that NpPP2-B10 likely participates in the plant immune response by mediating the ubiquitin protease pathway. In conclusion, our study provides some important insights concerning NpPP2-B10-mediated regulation of tobacco growth and resistance.

Odorant-Binding Proteins and Chemosensory Proteins in Spodoptera frugiperda: From Genome-Wide Identification and Developmental Stage-Related Expression Analysis to the Perception of Host Plant Odors, Sex Pheromones, and Insecticides

Spodoptera frugiperda is a worldwide generalist pest with remarkable adaptations to environments and stresses, including developmental stage-related behavioral and physiological adaptations, such as diverse feeding preferences, mate seeking, and pesticide resistance. Insects’ odorant-binding proteins (OBPs) and chemosensory proteins (CSPs) are essential for the chemical recognition during behavioral responses or other physiological processes. The genome-wide identification and the gene expression patterns of all these identified OBPs and CSPs across developmental stage-related S. frugiperda have not been reported. Here, we screened for genome-wide SfruOBPs and SfruCSPs, and analyzed the gene expression patterns of SfruOBPs and SfruCSPs repertoires across all developmental stages and sexes. We found 33 OBPs and 22 CSPs in the S. frugiperda genome. The majority of the SfruOBP genes were most highly expressed in the adult male or female stages, while more SfruCSP genes were highly expressed in the larval or egg stages, indicating their function complementation. The gene expression patterns of SfruOBPs and SfruCSPs revealed strong correlations with their respective phylogenic trees, indicating a correlation between function and evolution. In addition, we analyzed the chemical-competitive binding of a widely expressed protein, SfruOBP31, to host plant odorants, sex pheromones, and insecticides. Further ligands binding assay revealed a broad functional related binding spectrum of SfruOBP31 to host plant odorants, sex pheromones, and insecticides, suggesting its potential function in food, mate seeking, and pesticide resistance. These results provide guidance for future research on the development of behavioral regulators of S. frugiperda or other environmentally friendly pest-control strategies.

Odorant-Binding and Chemosensory Proteins in Anthonomus eugenii (Coleoptera: Curculionidae) and Their Tissue Expression

The pepper weevil Anthonomus eugenii is one of the most damaging pests to the pepper crop. To offer alternative management strategies to insecticides, several studies have identified the semiochemicals that are involved in the pepper weevil's aggregation and mating behavior; however, there is no information on its perireceptor molecular mechanism, to date. In this study, bioinformatics tools were used to functionally annotate and characterize the A. eugenii head transcriptome and their probable coding proteins. We identified twenty-two transcripts belonging to families related to chemosensory processes, seventeen corresponding to odorant-binding proteins (OBP), and six to chemosensory proteins (CSP). All results matched with closely related Coleoptera: Curculionidae homologous proteins. Likewise, twelve OBP and three CSP transcripts were experimentally characterized by RT-PCR in different female and male tissues. The results by sex and tissue display the different expression patterns of the AeugOBPs and AeugCSPs; some are present in both sexes and all tissues, while others show expressions with higher specificity, which suggests diverse physiological functions in addition to chemo-detection. This study provides information to support the understanding of odor perception in the pepper weevil.

Plant volatile ligands for male-biased MmedOBP14 stimulate orientation behavior of the parasitoid wasp Microplitis mediator

As an important class of chemosensory-associated proteins, odorant binding proteins (OBPs) play a key role in the perception of olfactory signals for insects. Parasitoid wasp Microplitis mediator relies on its sensitive olfactory system to locate host larvae of Noctuidae and Geometridae. In the present study, MmedOBP14, a male-biased OBP in M. mediator, was functionally investigated. In fluorescence competitive binding assays, the recombinant MmedOBP14 showed strong binding abilities to five plant volatiles: β-ionone, 3,4-dimethylacetophenone, 4-ethylacetophenone, acetophenone and ocimene. Homology modeling and molecular docking results indicated that the binding sites of all five ligands were similar and concentrated in the binding pocket of MmedOBP14. Except acetophenone, the remaining four ligands at 1, 10 and 100 μg/μL caused strong antennal electrophysiological responses in adults M. mediator, and males showed more obvious EAG responses to most ligands than females. In behavioral trials, males were attracted by low concentrations of MmedOBP14 ligands, whereas high doses of β-ionone and acetophenone had a repellent effect on males. Moreover, 1 μg/μL of 3,4-dimethylacetophenone showed the strongest attractiveness to female wasps. These findings suggest that MmedOBP14 may play a more important role in the perception of plant volatiles for male wasps to locate habitat, supplement nutrition and search partners.

Improved genome assembly provides new insights into the environmental adaptation of the American cockroach, Periplaneta americana

The synanthropic pest and a model organism for entomological research, American cockroach, Periplaneta americana (Linnaeus), can survive in unfavorable environments for humans. To investigate the genetic mechanisms of success in environmental adaptation of P. americana, we de novo reassembled its whole genome based on next-generation sequencing and PacBio sequencing. The final genome reassembly consisted of approximately 3.34 Gb with scaffold N50 of 465.51 Kb. The completeness (95.4%) of the complete genome was evaluated with single-copy orthologous genes using BUSCO. We identified 18,618 protein-coding genes, 16,443 (88.32%) of which were well supported by public protein databases. We identified 482.04 Mb (approximately 14.45%) repeat elements, 1,385,093 perfect microsatellites simple sequence repeats in P. americana genome, which was higher than other four Blattaria insects. Comparative genomics analysis revealed obvious expansion in the gene families associated with chemoreception (olfactory receptors, gustatory receptors, ionotropic glutamate receptors, chemosensory protein, and sensory neuron membrane protein), which provided the necessary information for functional characterization of the chemosensory receptors of P. americana, with potential for new or refined applications of semiochemicals-based control of this pest insect. Similarly, gene families (cytochrome P450s, carboxyl/choline esterases, and UDP-glycosyl-transferases) encoding receptors for bitter or toxic substances and detoxification enzymes were obviously expanded in P. americana, enabling its ability to detect and detoxify many toxins. Enrichment analysis of positively selected genes in P. americana revealed items associated with metabolic process and catalytic activity, which possibly contributed to the pesticide resistance of P. americana. We also analyzed the homologs to antimicrobial peptide genes reported in the Drosophila genome, and identified two attacins and seven defensins in P. americana. Our data and findings will substantially facilitate molecular studies in P. americana, including elucidation of detoxification mechanisms of xenobiotic, as well as development of new pest management strategies for the control of pests like P. americana.

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.

Differential Gene Expression Correlates with Behavioural Polymorphism during Collective Behaviour in Cockroaches

Simple Summary

It is currently well accepted that animals differ from one another in their behaviour and tendency to perform actions, a property we refer to as animal personality. In group-living animals, variation in animal personality can be important to determine group survival, as it determines how individuals interact with each other and with their environment. However, we have little knowledge of the proximal mechanisms underlying personality, particularly in group-living organisms. Here, we investigate the relationship between gene expression and two behavioural types (bold and shy) in a gregarious species: the American cockroach. Our results show that bold individuals have upregulated genes with functions associated with sensory activity (phototaxis and odour detection) and aggressive/dominant behaviour, and suggest that social context can modulate gene expression related to bold/shy characteristics. This work could help identify genes important in the earliest stages of group living and social life, and provides a first step toward establishing cockroaches as a focal group for the study of the evolution of sociality.

Abstract

Consistent inter-individual variation in the propensity to perform different tasks (animal personality) can contribute significantly to the success of group-living organisms. The distribution of different personalities in a group influences collective actions and therefore how these organisms interact with their environment. However, we have little understanding of the proximate mechanisms underlying animal personality in animal groups, and research on this theme has often been biased towards organisms with advanced social systems. The goal of this study is to investigate the mechanistic basis for personality variation during collective behaviour in a species with rudimentary societies: the American cockroach. We thus use an approach which combines experimental classification of individuals into behavioural phenotypes (‘bold’ and ‘shy’ individuals) with comparative gene expression. Our analyses reveal differences in gene expression between behavioural phenotypes and suggest that social context may modulate gene expression related to bold/shy characteristics. We also discuss how cockroaches could be a valuable model for the study of genetic mechanisms underlying the early steps in the evolution of social behaviour and social complexity. This study provides a first step towards a better understanding of the molecular mechanisms associated with differences in boldness and behavioural plasticity in these organisms.

Odorant Binding Protein C17 Contributes to the Response to Artemisia vulgaris Oil in Tribolium castaneum

The red flour beetle, Tribolium castaneum (T. castaneum), generates great financial losses to the grain storage and food processing industries. Previous studies have shown that essential oil (EO) from Artemisia vulgaris (A. vulgaris) has strong contact toxicity to larvae of the beetle, and odorant-binding proteins (OBPs) contribute to the defense of larvae against A. vulgaris. However, the functions of OBPs in insects defending against plant oil is still not clear. Here, expression of one OBP gene, TcOBPC17, was significantly induced 12–72 h after EO exposure. Furthermore, compared to the control group, RNA interference (RNAi) against TcOBPC17 resulted in a higher mortality rate after EO treatment, which suggests that TcOBPC17 involves in the defense against EO and induces a declining sensitivity to EO. In addition, the tissue expression profile analysis revealed that the expression of TcOBPC17 was more abundant in the metabolic detoxification organs of the head, fat body, epidermis, and hemolymph than in other larval tissue. The expression profile of developmental stages showed that TcOBPC17 had a higher level in early and late adult stages than in other developmental stages. Taken together, these results suggest that TcOBPC17 could participate in the sequestration process of exogenous toxicants in T. castaneum larvae.

The molecular identification, odor binding characterization, and immunolocalization of odorant-binding proteins in Liriomyza trifolii

The Liriomyza trifolii is a highly invasive polyphagia pest. Understanding the physiological functions of odorant binding proteins (OBPs) in the chemical communication of L. trifolii can lead to effective pest management strategies. Seven full-length OBPs were identified by transcriptome screening of L. trifolii adults. Bioinformatics analyses classified the seven OBPs into two subfamilies (six classic OBPs, one minus-C OBP). The analysis of their expression in different development stages revealed that LtriOBP5 was highly expressed in the larval stage, LtriOBP4 in the pupa stage, and LtriOBP1, 2, 3, 6, 7 in the adult stage; the expression levels were higher in male adults than in females. The analysis of different tissues showed high expression of LtriOBP1, 3, 6, 7 in the antennae, which were selected for in vitro purification. To explore the ligand compounds of OBPs, fluorescence competitive binding experiments were performed. Immunofluorescence localization revealed that LtriOBP1, 3, 6, 7 showed strong binding abilities to plant volatiles and were located in the antennae, implying that LtriOBP1, 3, 6, 7 may play key roles in olfaction, such as host location. LtriOBP6 and LtriOBP7 had strong binding abilities to specific herbivore-induced plant volatiles, suggesting LtriOBP6 and LtriOBP7 may also play critical roles in chemoreception. This study provides preliminary exploration of the olfactory perception mechanism of L. trifolii, which can be used as a basis to design insect behavior regulators and develop highly effective insecticides using mixture of ligands and known pesticides.

Appraisal of MsepCSP14 for chemosensory functions in Mythimna separata

Chemosensory proteins (CSPs) have great contributions in performing diverse functions in insects. However, physiological appraisal of chemosensory protein genes still remains elusive in insects. We studied expression patterns and binding affinities of MsepCSP14, a chemosensory protein, in Mythimna separata. The distinct functions of MsepCSP14 were validated by employing different molecular techniques. The MsepCSP14 had high resemblance of sequence with chemosensory proteins of other insect family members. The MsepCSP14 expression was higher in antennal tissues of females than other tissues. Fluorescence binding assay validated that binding of nine out of 21 ligands to MsepCSP14 was higher at pH 7.4 than at pH 5.0. Three dimensional modeling (3D) and docking analysis predicted that amino acid residues of MsepCSP14 were involved in binding of compounds, and behavior assay displayed that adults of M. separata considerably responded to four volatiles from compounds demonstrating strong binding ability to MsepCSP14. Results of the present study suggest that MsepCSP14 is likely to mediate chemosensory functions in M. separata.

Sex- and stage-dependent expression patterns of odorant-binding and chemosensory protein genes in Spodoptera exempta

As potential molecular targets for developing novel pest management strategies, odorant-binding proteins (OBPs) and chemosensory proteins (CSPs) have been considered to initiate odor recognition in insects. Herein, we investigated the OBPs and CSPs in a major global crop pest (Spodoptera exempta). Using transcriptome analysis, we identified 40 OBPs and 33 CSPs in S. exempta, among which 35 OBPs and 29 CSPs had intact open reading frames. Sequence alignment indicated that 30 OBPs and 23 CSPs completely contained the conserved cysteines. OBPs of lepidopteran insects usually belonged to classical, minus-C, and plus-C groups. However, phylogenetic analyses indicated that we only identified 28 classical and seven minus-C OBPs in S. exempta, suggesting that we might have missed some typical OBPs in lepidopteran insects, probably due to their low expression levels. All of the CSPs from S. exempta clustered with the orthologs of other moths. The identification and expression of the OBPs and CSPs were well studied in insect adults by transcriptional analyses, and herein we used samples at different stages to determine the expression of OBPs and CSPs in S. exempta. Interestingly, our data indicated that several OBPs and CSPs were especially or more highly expressed in larvae or pupae than other stages, including three exclusively (SexeOBP13, SexeOBP16 and SexeCSP23) and six more highly (SexeOBP15, SexeOBP37, SexeCSP4, SexeCSP8, SexeCSP19, and SexeCSP33) expressed in larvae, two exclusively (SexeCSP6 and SexeCSP20) and three more highly (SexeOBP18, SexeCSP17, and SexeCSP26) expressed in pupae. Usually, OBPs and CSPs had both male- and female-biased expression patterns in adult antennae. However, our whole-body data indicated that all highly expressed OBPs and CSPs in adults were male-biased or did not differ, suggesting diverse OBP and CSP functions in insect adults. Besides identifying OBPs and CSPs as well as their expression patterns, these results provide a molecular basis to facilitate functional studies of OBPs and CSPs for exploring novel management strategies to control S. exempta.

Two carboxylesterase genes in Plutella xylostella associated with sex pheromones and plant volatiles degradation

BACKGROUND

Carboxyl/cholinesterases (CCEs) are thought to play a pivotal role in the degradation of sex pheromones and plant-derived odorants in insects, but their exact biochemistry and physiological functions remain unclear.

RESULTS

In this study, two paralogous antennae-enriched CCEs from Plutella xylostella (PxylCCE16a and 16c) were identified and functionally characterized. High-purity protein preparations of active recombinant PxylCCE16a and 16c have been obtained from Sf9 insect cells by Ni²⁺ affinity purification. Our results revealed that the purified recombinant PxylCCE016c is able to degrade two sex pheromone components Z9-14:Ac and Z11-16:Ac at 27.64 ± 0.79% and 24.40 ± 3.07%, respectively, while PxylCCE016a presented relatively lower activity. Additionally, a similar difference in activity was measured in plant-derived odorants. Furthermore, both CCEs displayed obvious preferences for the two sex pheromone components, especially on Z11-16:Ac (K_m values are in the range 7.82-45.06 μmol L^-1 ) which much lower than plant odorants (K_m values are in the range 1290-4030 μmol L^-1 ). Furthermore, the activity of the two newly identified CCEs is pH-dependent. The activity at pH 6.5 is obviously higher than that at pH 5.0. Interestingly, only PxylCCE016c can be inhibited by a common esterase inhibitor triphenyl phosphate (TPP) with LC₅₀ of 1570 ± 520 μmol L^-1 .

CONCLUSION

PxylCCE16c plays a more essential role in odorant degradation than PxylCCE16a. Moreover, the current study provides novel potential pesticide targets for the notorious moth Plutella xylostella. © 2021 Society of Chemical Industry.

Expression, Affinity, and Functional Characterization of the Specific Binding of Two Putative Pheromone-Binding Proteins in the Omnivorous German Cockroach Blattella germanica

The German cockroach Blattella germanica (L.) is an important pest in medical, veterinary, and public health. Studies on the olfaction mechanism of hemimetabolous insects have rarely been reported, especially in cockroaches. Pheromone-binding proteins (PBPs) play a vital role in insect sex pheromone recognition, which solubilize and carry the hydrophobic pheromonal compounds through the antennal lymph to receptors. In this study, two potential PBPs (BgerOBP26 and BgerOBP40) were identified on the basis of their biased expression in male antennae using tissue transcriptome data and verified by the quantitative real-time polymerase chain reaction approach. We then expressed and purified the two identified odorant-binding proteins (OBPs) using the Escherichia coli expression system and affinity purification. In vitro binding studies showed that the two OBPs display stronger binding affinities to the female volatile sex pheromone blattellaquinone than to its analogues and contact sex pheromone components. Finally, three-dimensional modeling of the two OBPs and dock conformation with sex pheromone molecules showed BgerOBP26 has a larger odorant cavity and more conservative active amino acid residues than BgerOBP40. These results illuminated the binding characteristics of potential PBPs of B. germanica, which could lay the groundwork for improved understanding of many aspects of the chemical ecology of B. germanica. Moreover, this information complements the understanding of the olfactory molecular mechanism in cockroaches and provides potential gene targets for B. germanica control.

Expression Profiles and Binding Properties of the Chemosensory Protein PxylCSP11 from the Diamondback Moth, Plutella xylostella (Lepidoptera: Plutellidae)

The diamondback moth, Plutella xylostella L. (Lepidoptera: Plutellidae) is one of the most destructive pests to cruciferous plants worldwide. The oligophagous moth primarily utilizes its host volatiles for foraging and oviposition. Chemosensory proteins (CSPs) are soluble carrier proteins with low molecular weight, which recognize and transport various semiochemicals in insect chemoreception. At present, there is limited information on the recognition of host volatiles by CSPs of P. xylostella. Here, we investigated expression patterns and binding characteristics of PxylCSP11 in P. xylostella. The open reading frame of PxylCSP11 was 369-bp encoding 122 amino acids. PxylCSP11 possessed four conserved cysteines, which was consistent with the typical characteristic of CSPs. PxylCSP11 was highly expressed in antennae, and the expression level of PxylCSP11 in male antennae was higher than that in female antennae. Fluorescence competitive binding assays showed that PxylCSP11 had strong binding abilities to several ligands, including volatiles of cruciferous plants, and (Z)-11-hexadecenyl acetate (Z11-16:Ac), a major sex pheromone of P. xylostella. Our results suggest that PxylCSP11 may play an important role in host recognition and spouse location in P. xylostella.

Odorant-Binding Proteins Contribute to the Defense of the Red Flour Beetle, Tribolium castaneum, Against Essential Oil of Artemisia vulgaris

The function of odorant-binding proteins (OBPs) in insect chemodetection has been extensively studied. However, the role of OBPs in the defense of insects against exogenous toxic substances remains elusive. The red flour beetle, Tribolium castaneum, a major pest of stored grains, causes serious economic losses for the agricultural grain and food processing industries. Here, biochemical analysis showed that essential oil (EO) from Artemisia vulgaris, a traditional Chinese medicine, has a strong contact killing effect against larvae of the red flour beetle. Furthermore, one OBP gene, TcOBPC11, was significantly induced after exposure to EO. RNA interference (RNAi) against TcOBPC11 led to higher mortality compared with the controls after EO treatment, suggesting that this OBP gene is associated with defense of the beetle against EO and leads to a decrease in sensitivity to the EO. Tissue expression profiling showed that expression of TcOBPC11 was higher in the fat body, Malpighian tubule, and hemolymph than in other larval tissues, and was mainly expressed in epidermis, fat body, and antennae from the early adult. The developmental expression profile revealed that expression of TcOBPC11 was higher in late larval stages and adult stages than in other developmental stages. These data indicate that TcOBPC11 may be involved in sequestration of exogenous toxicants in the larvae of T. castaneum. Our results provide a theoretical basis for the degradation mechanism of exogenous toxicants and identify potential novel targets for controlling the beetle.

Identification of chemosensory genes from the antennal transcriptome of Semiothisa cinerearia

Olfaction plays vital roles in the survival and reproduction of insects. The completion of olfactory recognition requires the participation of various complex protein families. However, little is known about the olfactory-related proteins in Semiothisa cinerearia Bremer et Grey, an important pest of Chinese scholar tree. In this study, we sequenced the antennal transcriptome of S. cinerearia and identified 125 olfactory-related genes, including 25 odorant-binding proteins (OBPs), 15 chemosensory proteins (CSPs), two sensory neuron membrane proteins (SNMPs), 52 odorant receptors (ORs), eight gustatory receptors (GRs) and 23 ionotropic receptors (IRs). BLASTX best hit results and phylogenetic analyses indicated that these genes were most identical to their respective orthologs from Ectropis obliqua. Further quantitative real-time PCR (qRT-PCR) analysis revealed that three ScinOBPs and three ScinORs were highly expressed in male antennae, while seven ScinOBPs and twelve ScinORs were female-specifically expressed. Our study will be useful for the elucidation of olfactory mechanisms in S. cinerearia.

Odorant Binding Proteins and Chemosensory Proteins in Episyrphus balteatus (Diptera: Syrphidae): Molecular Cloning, Expression Profiling, and Gene Evolution

Aphidophagous syrphids (Diptera: Syrphidae) are important insects in agroecosystems for pollination and biological control. Insect chemoreception is essential for these processes and for insect survival and reproduction; however, molecular determinants is not well understood for these beneficial insects. Here, we used recent transcriptome data for the common hoverfly, Episyrphus balteatus, to characterize key molecular components of chemoreception: odorant-binding proteins (OBPs) and chemosensory proteins (CSPs). Six EbalCSPs and 44 EbalOBPs were cloned from this species, and sequence analysis showed that most share the characteristic hallmarks of their protein family, including a signal peptide and conserved cysteine signature. Some regular patterns and key conserved motifs of OBPs and CSPs in Diptera were identified using the online tool MEME. Motifs were also compared among the three OBP subgroups. Quantitative real-time PCR (qRT-PCR) showed that most of these chemosensory genes were expressed in chemosensory organs, suggesting these genes have chemoreceptive functions. An overall comparison of the Ka/Ks values of orthologous genes in E. balteatus and another predatory hoverfly species to analyze the evolution of these olfactory genes showed that OBPs and CSPs are under strong purifying selection. Overall, our results provide a molecular basis for further exploring the chemosensory mechanisms of E. balteatus, and consequently, may help us to understand the tritrophic interactions among plants, herbivorous insects, and natural enemies.

Identification and comparative expression profiles of chemosensory genes in major chemoreception organs of a notorious pests, Laodelphax striatellus

The small brown planthopper, Laodelphax striatellus (Stål) (SBPH), is a notorious rice pest in East Asia and damages the host by feeding on the phloem and transmitting virus particles. Although SBPH relies on chemosensory perception for seeking the host, courtship, selecting oviposition sites and spreading virus particles, a systematic study of chemosensory genes in SBPH is lacking. In this study, we identified multi-gene chemosensory families from the transcriptome of SBPH olfactory organs and analyzed their expression patterns in male and female tissues. Among the chemosensory genes, 14 odorant-binding proteins (OBPs), 12 chemosensory proteins (CSPs), 7 sensory neuron membrane proteins (SNMPs) and 95 odorant receptors (ORs) were identified and annotated in SBPH olfactory organs. Based on expression profile and phylogenetic analysis, LstrOBP1, 2, 5, 6, 7, 10, LstrSNMP1, and most LstrORs showed an antennae-enriched expression pattern, which suggests an olfactory role for these genes. Relative expression of LstrOBPs was validated by quantitative real-time PCR. Our findings provide the genetic information for disrupting the feeding behavior of SBPH, which is essential for developing eco-friendly pest management technologies.

CRISPR/Cas9 mediated gene knockout reveals a more important role of PBP1 than PBP2 in the perception of female sex pheromone components in Spodoptera litura

Three different pheromone binding proteins (PBPs) can typically be found in the sensilla lymph of noctuid moth antennae, but their relative contributions in perception of the sex pheromone is rarely verified in vivo. Previously, we demonstrated that SlitPBP3 plays a minor role in the sex pheromone detection in Spodoptera litura using the CRISPR/Cas9 system. In the present study, the roles of two other SlitPBPs (SlitPBP1 and SlitPBP2) are further verified using the same system. First, by co-injection of Cas9 mRNA/sgRNA into newly laid eggs, a high rate of target mutagenesis was induced, 51.5% for SlitPBP1 and 46.8% for SlitPBP2 as determined by restriction enzyme assay. Then, the homozygous SlitPBP1 and SlitPBP2 knockout lines were obtained by cross-breeding. Finally, using homozygous knockout male moths, we performed electrophysiological (EAG recording) and behavioral analyses. Results showed that knockout of either SlitPBP1 or SlitPBP2 in males decreased EAG response to each of the 3 sex pheromone components (Z9,E11-14:Ac, Z9,E12-14:Ac and Z9-14:Ac) by 53%, 60% and 63% (for SlitPBP1 knockout) and 40%, 43% and 46% (for SlitPBP2 knockout), respectively. These decreases in EAG responses were similar among 3 pheromone components, but were more pronounced in SlitPBP1 knockout males than in SlitPBP2 knockout males. Consistently, behavioral assays with the major component (Z9,E11-14:Ac) showed that SlitPBP1 knockout males responded in much lower percentages than SlitPBP2 knockout males in terms of orientation to the pheromone, along with reduction in close range behaviors such as hairpencil display and mating attempt. Taken together, this study provides direct functional evidence for the roles of SlitPBP1 and SlitPBP2, as well as their relative importance (SlitPBP1 > SlitPBP2) in the sex pheromone perception. This information is valuable in understanding mechanisms of sex pheromone perception and may facilitate the development of PBP-targeted pest control techniques.

Evolution and functional analysis of odorant-binding proteins in three rice planthoppers: Nilaparvata lugens, Sogatella furcifera, and Laodelphax striatellus

BACKGROUND

The white-backed planthopper (WBPH) Sogatella furcifera, the brown planthopper (BPH) Nilaparvata lugens, and the small brown planthopper (SBPH) Laodelphax striatellus are three notorious rice pests that cause annual losses in rice yield through sap-sucking and virus transmission. Odorant-binding proteins (OBPs) are crucial olfactory genes involved in host-seeking behavior.

RESULTS

We discovered the presence of 12, 12, and 16 OBPs in WBPH, BPH, and SBPH, respectively, including two novel OBPs in BPH and seven novel OBPs in SBPH. Phylogenetic analysis indicated that most of these OBPs have homologous genes, and one group (SfurOBP11, NlugOBP8, and LstrOBP2) show a slower evolution rate and are more conserved. Further, in vitro binding studies demonstrated that the three OBPs have similar binding affinities for some rice plant volatiles. Finally, RNA interference (RNAi) successfully inhibited the mRNA expression of the three OBPs, and in vivo behavioral tests showed that the OBP-deficient rice planthoppers were partly anosmic and lost some of their ability to locate rice plants.

CONCLUSION

These results demonstrate the crucial role of the rice planthopper OBP genes in seeking rice plants. This information complements the current genetic resources for the development of RNAi-based transgenic rice and other pest management technologies. © 2018 Society of Chemical Industry.

Antennal transcriptome analysis of the maize weevil Sitophilus zeamais: Identification and tissue expression profiling of candidate odorant-binding protein genes

Our bioassays reviewed that antennae played crucial roles in the responses of maize weevil (Sitophilus zeamais) to food and sex volatiles. In order to identify the maize weevil odorant-binding protein (OBP) genes, we analyzed its antennal transcriptome. In total, 21,587,928 high-quality clean reads were obtained from RNA-seq, 52,206 unigenes were assembled, and 25,744 unigenes showed significant similarity ( E value < 10 ^-5 ) to known proteins in the NCBI nonredundant protein database. From those unigenes, we identified 41 candidate OBP proteins, which could be categorized into dimeric OBPs subfamily, minus-C OBPs subfamily, and classical OBPs subfamily. Phylogenic analysis indicated that most maize weevil OBPs were closely related to their orthologues in other beetles of the Superfamily Curculionoidea. We further investigated the expression profiles of those candidate OBP genes by quantitative real-time polymerase chain reaction. Twenty-six of forty-one maize weevil OBP genes were highly expressed in the antennae or other parts of the head. The rest were expressed in the legs, wings, or other tested tissues. The antennal transcriptomic data and candidate OBP genes described here provide a basis for the functional studies of the maize weevil chemical perception, which are potential novel targets for pest control strategies.

Expression and Functional Analysis of Two Odorant-Binding Proteins from Bradysia odoriphaga (Diptera: Sciaridae)

Two OBP genes, BodoOBP1 and BodoOBP2, were cloned from Bradysia odoriphaga, a major agricultural pest of Chinese chives. The amino acid sequence alignment of both BodoOBPs showed high similarity. Fluorescence competitive binding assays revealed that both BodoOBPs have a moderate binding affinity to dipropyl trisulfide. Tissue expression profiles indicated that both BodoOBPs are antennae-specific and more abundant in the male antennae than in the female antennae. Developmental expression profile analysis indicated that expression levels of both BodoOBPs were higher in the male adult stage than in the other developmental stages. Both BodoOBPs also showed differential expression in pre- and postmating adults. RNAi assays indicated that ability of dsOBPs-treated males to detect females was significantly reduced compared to controls. Attraction of plant volatile dipropyl trisulfide to dsOBPs-treated adults was also significantly lower than in the control. Our findings indicate that both BodoOBPs are involved in host-seeking behavior and in detecting sex pheromones.

Niemann-Pick proteins type C2 are identified as olfactory related genes of Pardosa pseudoannulata by transcriptome and expression profile analysis

In arthropods, the large majority of studies on olfaction have been mainly focused on insects, whereas little on Arachnida, even though olfaction is very important in arachnid behavior. Pardosa pseudoannulata is one of the most common wandering spiders in rice fields, as the important natural enemy against a range of pests. However, little is known about the potential chemosensory proteins involved in olfactory behavior of these spiders. Niemann-Pick proteins type C2 (NPC2) as a new class of binding and transport proteins for semiochemicals in arthropods especially ticks and mites has received more attention in recent years. In this study, six NPC2s namely PpseNPC1-6 were newly identified in the appendages of P. pseudoannulata based on transcriptome data. A phylogenetic analysis indicated that all of P. pseudoannulata NPC2s were clustered together forming one clade with high posterior probability values. In addition, the sequences shared the same subclade with the NPC2 sequences of ticks and scorpion. The motif-patterns indicated that PpseNPC2-5 had the common pattern with the two-spotted spider mite Tetranychus urticae and the ant Trachymyrmex cornetzi. Furthermore, quantitative real-time PCR (qPCR) measurements were conducted to evaluate the expression profile of these genes in various tissues of P. pseudoannulata. It was found that most NPC2s (PpseNPC2-1, PpseNPC2-2, PpseNPC2-5 and PpseNPC2-6) were highly expressed in adult pedipalps and chelicerae. Owing to the functional olfactory organs in Chelicerata of pedipalps, our results supported a putative role of NPC2s as new odorant carriers in P. pseudoannulata.

A chemosensory protein MsepCSP5 involved in chemoreception of oriental armyworm Mythimna separata

Chemosensory proteins (CSPs) have been suggested to perform several functions in insects, including chemoreception. To find out whether MsepCSP5 identified from Mythimna separata shows potential physiological functions in olfaction, gene expression profiles, ligand-binding experiments, molecular docking, RNA interference, and behavioral test were performed. Results showed that MsepCSP5 was highly expressed in female antennae. MsepCSP5 showed high binding affinities to a wide range of host-related semiochemicals, and displayed that 26 out of 35 candidate volatiles were highly bound (Ki < 10 µM) at pH 5.0 rather than pH 7.4. The binding sites of MsepCSP5 to candidate volatiles were well predicted by three-dimensional structure modeling and molecular docking experiments. Pursuing further, biological activities of M. separata to highly bound compounds elicited strong behavioral responses, such as alcoholic compounds displayed strong attractiveness whereas terpenes showed repellency to M. separata. The transcript expression level of MsepCSP5 gene significantly decreased after injecting target dsRNAs, and resulted in non-significant preference responses of M. separata to semiochemicals, such as 3-pentanol and 1-octene-3-ol. In conclusion, MsepCSP5 may involve in semiochemical reception of M. separata.

Binding affinity characterization of an antennae-enriched chemosensory protein from the white-backed planthopper, Sogatella furcifera (Horváth), with host plant volatiles

The white-backed planthopper (WBPH) Sogatella furcifera is a notorious rice pest in Asia. Olfaction is crucial for the WBPH to seek and locate rice plants. However, its mechanism is still not fully understood. Chemosensory proteins (CSPs) are some of the important olfactory-related proteins. In this study, we first used a bacterial system to successfully express the recombinant, antennae-enriched protein SfurCSP5. Further, competitive fluorescence binding assays with 86 candidate ligands, including some known rice plant volatiles, showed that SfurCSP5 has high affinities for 2-tridecanone, 2-pentadecanone, and β-ionone, which are known to be present in volatile mixtures that can attract rice planthoppers, and produced Ki values of 4.89, 4.09, and 1.39 μmol/L, respectively. Additionally, homology modeling of the protein structure of SfurCSP5 showed that it possesses five α-helixes (α-1, α-2, α-3, α-4, and α-5), which is a non-typical feature of the insect CSPs. Finally, ligand docking results revealed that Leu-44, Ile-64, Phe-90, Trp-98, and Phe-101 are five hydrophobic residues that interact with all of the ligands, indicating their key involvement in the binding of SfurCSP5. Our study lays the foundation for an understanding of the olfaction mechanism of rice planthoppers.

Distinct binding affinities of odorant-binding proteins from the natural predator Chrysoperla sinica suggest different strategies to hunt prey

Chrysoperla sinica is an important natural predator of many notorious agricultural pests. Understanding its olfactory mechanism can help enhance the effectiveness of C. sinica in biological control. In the present study, we investigated the tissue expression patterns of 12 odorant-binding protein (OBP) genes from C. sinica (CsinOBPs). The results of quantitative real-time polymerase chain reaction (qPCR) showed that CsinOBP1, CsinOBP2, CsinOBP3, CsinOBP4, CsinOBP6, CsinOBP7, CsinOBP9, CsinOBP10, and CsinOBP12 were predominantly expressed in the antennae of both sexes, indicating their roles in olfaction. Additionally, the qPCR analysis revealed that the 12 CsinOBP genes had distinct expression patterns, while the motif-pattern investigation suggested that the OBPs had different ligands. The ligand-binding assay showed that CsinOBP1 and CsinOBP10 had broader binding spectra than did the other OBPs. Thus, CsinOBP1 was able to bind not only plant volatiles (such as farnesol, cis-3-hexenyl hexanoate, geranylacetone, β-ionone, 2-tridecanone, and trans-nerolidol) but also the aphid alarm pheromone (E)-β-farnesene. On the other hand, CsinOBP2 and CsinOBP6 exhibited relatively narrow binding spectra, only binding ethyl benzoate. The study also identified several compounds that can potentially be used to develop slow-release agents attracting C. sinica and to improve search strategies for insect pest control.

Expression Profile and Functional Characterization Suggesting the Involvement of Three Chemosensory Proteins in Perception of Host Plant Volatiles in Chilo suppressalis (Lepidoptera: Pyralidae)

The high sensitivity of the olfactory system is essential for feeding and oviposition in moth insects, and some chemosensory proteins (CSPs) are thought to play roles in this system by binding and carrying hydrophobic odorants across the aqueous sensillar lymph. In this study, to identify the olfactory CSPs from a repertoire of 21 CSP members in the notorious rice pest Chilo suppressalis (Walker) (Lepidoptera: Pyralidae), tissue expression patterns were firstly examined by quantitative real-time polymerase chain reaction (qPCR). It showed that CSP2 was antennae specific and seven more CSPs (CSP1, 3, 4, 6, 15, 16, and 17) were antennae biased in expression, suggesting their olfactory roles; while other CSPs were multiple-tissue expressed and non-antennae biased, suggesting other functions for these genes. To further determine the ligand binding specificity, three putative olfactory genes (CSP1-3) were expressed in Escherichia coli cells, and binding affinity of these three recombinant CSP proteins were measured for 35 plant volatiles by the ligand binding assays. CSP1 and CSP2 exhibited high binding affinities (Ki ≤ 10.00 µM) for four (2-tridecanone, benzaldehyde, laurinaldehyde and 2-pentadecanone) and two (2-heptanol and (+)-cedrol) host plant volatiles, respectively; the three CSPs also showed moderate binding affinity (Ki = 10.01-20.00 µM) for 16 plant volatiles. Our study suggests that the three CSPs play essential roles in the perception of host plant volatiles, providing bases for the elucidation of olfactory mechanisms in this important pyralid pest.

Functional Analysis of the Chemosensory Protein MsepCSP8 From the Oriental Armyworm Mythimna separata

Chemosensory proteins (CSPs) play important roles in chemosensation in insects, but their exact physiological functions remain elusive. In order to investigate the functions of CSPs in the oriental armyworm Mythimna separata, in the present study we explored expression patterns and binding characteristics of the CSP, MsepCSP8. The distinctive functions of MsepCSP8 were also validated by RNAi. The results showed that MsepCSP8 shares high sequence similarity with CSPs of other insect family members, including the characteristic four-cysteine signature motif. MsepCSP8 mRNA was specifically expressed in antennae of females at levels well above those in other tissues. Competitive binding assays confirmed that 20 out of 56 ligands bound more strongly to MsepCSP8 at pH 7.4 than at pH 5.0. Protein structure modeling and molecular docking analyses identified amino acid residues involved in binding volatile compounds, and behavioral response experiments showed that M. separata elicited significant responses to five volatiles from compounds displaying high binding affinity to MsepCSP8. MsepCSP8 transcript abundance was decreased by dsMsepCSP8 injection, which affected the behavioral responses of M. separata to representative semiochemicals. Our findings demonstrate that MsepCSP8 likely contributes to mediating responses of M. separata adults to plant volatiles.

Various Bee Pheromones Binding Affinity, Exclusive Chemosensillar Localization, and Key Amino Acid Sites Reveal the Distinctive Characteristics of Odorant-Binding Protein 11 in the Eastern Honey Bee, Apis cerana

Odorant-binding proteins (OBPs) are the critical elements responsible for binding and transporting odors and pheromones in the sensitive olfactory system in insects. Honey bees are representative social insects that have complex odorants and pheromone communication systems relative to solitary insects. Here, we first cloned and characterized OBP11 (AcerOBP11), from the worker bees antennae of Eastern honey bee, Apis cerana. Based on sequence and phylogenetic analysis, most sequences homologous to AcerOBP11 belong to the typical OBPs family. The transcriptional expression profiles showed that AcerOBP11 was expressed throughout the developmental stages and highly specifically expressed in adult antennae. Using immunofluorescence localization, AcerOBP11 in worker bee's antennae was only localized in the sensilla basiconica (SB) near the fringe of each segment. Fluorescence ligand-binding assay showed that AcerOBP11 protein had strong binding affinity with the tested various bee pheromones components, including the main queen mandibular pheromones (QMPs), methyl p-hydroxybenzoate (HOB), and (E)-9-oxo-2-decanoic acid (9-ODA), alarm pheromone (n-hexanol), and worker pheromone components. AcerOBP11 also had strong binding affinity to plant volatiles, such as 4-Allylveratrole. Based on the docking and site-directed mutagenesis, two key amino acid residues (Ile97 and Ile140) were involved in the binding of AcerOBP11 to various bee pheromones. Taken together, we identified that AcerOBP11 was localized in a single type of antennal chemosensilla and had complex ligand-binding properties, which confer the dual-role with the primary characteristics of sensing various bee pheromones and secondary characteristics of sensing general odorants. This study not only prompts the theoretical basis of OBPs-mediated bee pheromones recognition of honey bee, but also extends the understanding of differences in pheromone communication between social and solitary insects.

Silencing of Chemosensory Protein Gene NlugCSP8 by RNAi Induces Declining Behavioral Responses of Nilaparvata lugens

Chemosensory proteins (CSPs) play imperative functions in chemical and biochemical signaling of insects, as they distinguish and transfer ecological chemical indications to a sensory system in order to initiate behavioral responses. The brown planthopper (BPH), Nilaparvata lugens Stål (Hemiptera: Delphacidae), has emerged as the most destructive pest, causing serious damage to rice in extensive areas throughout Asia. Biotic characteristics like monophagy, dual wing forms, and annual long-distance migration imply a critical role of chemoreception in N. lugens. In this study, we cloned the full-length CSP8 gene from N. lugens. Protein sequence analysis indicated that NlugCSP8 shared high sequence resemblance with the CSPs of other insect family members and had the typical four-cysteine signature. Analysis of gene expression indicated that NlugCSP8 mRNA was specifically expressed in the wings of mated 3-day brachypterous females with a 175-fold difference compare to unmated 3-day brachypterous females. The NlugCSP8 mRNA was also highly expressed in the abdomen of unmated 5-day brachypterous males and correlated to the age, gender, adult wing form, and mating status. A competitive ligand-binding assay demonstrated that ligands with long chain carbon atoms, nerolidol, hexanal, and trans-2-hexenal were able to bind to NlugCSP8 in declining order of affinity. By using bioinformatics techniques, three-dimensional protein structure modeling and molecular docking, the binding sites of NlugCSP8 to the volatiles which had high binding affinity were predicted. In addition, behavioral experiments using the compounds displaying the high binding affinity for the NlugCSP8, revealed four compounds able to elicit significant behavioral responses from N. lugens. The in vivo functions of NlugCSP8 were further confirmed through the testing of RNAi and post-RNAi behavioral experiments. The results revealed that reduction in NlugCSP8 transcript abundance caused a decrease in behavioral response to representative attractants. An enhanced understanding of the NlugCSP8 is expected to contribute in the improvement of more effective and eco-friendly control strategies of BPH.

Sex- and Tissue-Specific Expression Profiles of Odorant Binding Protein and Chemosensory Protein Genes in Bradysia odoriphaga (Diptera: Sciaridae)

Bradysia odoriphaga is an agricultural pest insect affecting the production of Chinese chive and other liliaceous vegetables in China, and it is significantly attracted by sex pheromones and the volatiles derived from host plants. Despite verification of this chemosensory behavior, however, it is still unknown how B. odoriphaga recognizes these volatile compounds on the molecular level. Many of odorant binding proteins (OBPs) and chemosensory proteins (CSPs) play crucial roles in olfactory perception. Here, we identified 49 OBP and 5 CSP genes from the antennae and body transcriptomes of female and male adults of B. odoriphaga, respectively. Sequence alignment and phylogenetic analysis among Dipteran OBPs and CSPs were analyzed. The sex- and tissue-specific expression profiles of 54 putative chemosensory genes among different tissues were investigated by quantitative real-time PCR (qRT-PCR). qRT-PCR analysis results suggested that 22 OBP and 3 CSP genes were enriched in the antennae, indicating they might be essential for detection of general odorants and pheromones. Among these antennae-enriched genes, nine OBPs (BodoOBP2/4/6/8/12/13/20/28/33) were enriched in the male antennae and may play crucial roles in the detection of sex pheromones. Moreover, some OBP and CSP genes were enriched in non-antennae tissues, such as in the legs (BodoOBP3/9/19/21/34/35/38/39/45 and BodoCSP1), wings (BodoOBP17/30/32/37/44), abdomens and thoraxes (BodoOBP29/36), and heads (BodoOBP14/23/31 and BodoCSP2), suggesting that these genes might be involved in olfactory, gustatory, or other physiological processes. Our findings provide a starting point to facilitate functional research of these chemosensory genes in B. odoriphaga at the molecular level.

Identification, Expression Patterns, and Functional Characterization of Chemosensory Proteins in Dendroctonus armandi (Coleoptera: Curculionidae: Scolytinae)

The Chinese white pine beetle, Dendroctonus armandi Tsai and Li (Coleoptera: Curculionidae: Scolytinae), is a serious pest of coniferous forests in China. Thus, there is considerable interest in developing eco-friendly pest-control methods, with the use of semiochemicals as a distinct possibility. Olfaction is extremely important for fitness of D. armandi because it is the primary mechanism through which the insect locates hosts and mates. Thus, here we characterized nine full-length genes encoding chemosensory proteins (CSPs) from D. armandi. The genes were ubiquitously and multiply expressed across different developmental stages and adult tissues, indicating various roles in developmental metamorphosis, olfaction, and gustation. Ligand-binding assays implied that DarmCSP2 may be the carrier of D. armandi pheromones and various plant host volatiles. These volatiles were identified through RNA interference of DarmCSP2 as: (+)-α-pinene, (+)-β-pinene, (−)-β-pinene, (+)-camphene, (+)-3-carene, and myrcene. The systematic chemosensory functional analysis of DarmCSP2 in this study clarified the molecular mechanisms underlying D. armandi olfaction and provided a theoretical foundation for eco-friendly pest control.

Identification and Characterization of Odorant Binding Proteins in the Forelegs of Adelphocoris lineolatus (Goeze)

The chemosensory system is essential for insects to detect exogenous compounds, and odorant binding proteins (OBPs) play crucial roles in odorant binding and transduction. In the alfalfa plant bug Adelphocoris lineolatus, an important pest of multiple crops, our understanding of the physiological roles of antenna-biased OBPs has increased dramatically, whereas OBPs related to gustation have remained mostly unexplored. In this study, we employed RNA sequencing and RACE PCR methods to identify putative OBPs from the adult forelegs of both sexes. Eight candidate OBPs were identified, and three OBPs (AlinOBP15, 16, and 17) were novel. Full-length sequence alignment and phylogenetic analyses suggested that these three candidate OBPs had characteristics typical of the insect OBP family. AlinOBP16 and 17 displayed six highly conserved cysteines, placing them in the classic OBP subfamily, whereas AlinOBP15 resembled AlinOBP14 and clustered with the Plus-C clade. Quantitative real-time PCR (qRT-PCR) revealed distinct and significant tissue- and sex-biased expression patterns. AlinOBP15 was highly expressed in female heads, and AlinOBP16 and 17 were strongly expressed in female antennae. In particular, AlinOBP11, the most abundant OBP gene in our foreleg transcriptome dataset, was predominately expressed in adult legs. Furthermore, four types of sensilla hairs were observed on the forelegs of adult A. lineolatus, including sensilla trichodea, setae, and two types of sensilla chaetica (Sch1 and Sch2). Anti-AlinOBP11 antiserum strongly labeled the outer sensillum lymph of Sch2, implying that it has important gustatory functions in A. lineolatus. Our current findings provide evidence that OBPs can be functionally expressed in the tarsal gustatory sensilla of hemipteran mirid species, broadening our understanding of OBP chemosensory function in insects and facilitating the discovery of new functional targets for the regulation of insect host-searching behaviors.