Identification of candidate chemosensory genes by transcriptome analysis in Loxostege sticticalis Linnaeus

Genomic identification and evolutionary analysis of chemosensory receptor gene families in two Phthorimaea pest species: insights into chemical ecology and host adaptation

BACKGROUND

Insects rely on sophisticated sensitive chemosensory systems to sense their complex chemical environment. This sensory process involves a combination of odorant receptors (ORs), gustatory receptors (GRs) and ionotropic receptors (IRs) in the chemosensory system. This study focused on the identification and characterization of these three types of chemosensory receptor genes in two closely related Phthorimaea pest species, Phthorimaea operculella (potato tuber moth) and Phthorimaea absoluta (tomato leaf miner).

RESULTS

Based on manual annotation of the genome, we identified a total of 349 chemoreceptor genes from the genome of P. operculella, including 93 OR, 206 GR and 50 IR genes, while for P. absoluta, we identified 72 OR, 122 GR and 46 IR genes. Through phylogenetic analysis, we observed minimal differences in the number and types of ORs and IRs between the potato tuber moth and tomato leaf miner. In addition, we found that compared with those of tomato leaf miners, the gustatory receptor branch of P. operculella has undergone a large expansion, which may be related to P. absoluta having a narrower host range than P. operculella. Through analysis of differentially expressed genes (DEGs) of male and female antennae, we uncovered 45 DEGs (including 32ORs, 9 GRs, and 4 IRs).

CONCLUSIONS

Our research provides a foundation for exploring the chemical ecology of these two pests and offers new insights into the dietary differentiation of lepidopteran insects, while simultaneously providing molecular targets for developing environmentally friendly pest control methods based on insect chemoreception.

Identification of the odorant binding proteins of Western Flower Thrips (Frankliniella occidentalis), characterization and binding analysis of FoccOBP3 with molecular modelling, molecular dynamics simulations and a confirmatory field trial

Olfactory systems are indispensable for insects as they, including Western Flower Thrips (Frankliniella occidentalis), use olfactory cues for ovipositing and feeding. F. occidentalis use odorant binding proteins (OBPs) to transport semiochemicals to odorant receptors to induce a behavioural response from the sensillum lymph of the insect's antennae. This study identifies four OBPs of F. occidentalis and analyses their expression at three stages of growth: larvae, adult males and adult females. Further, it investigates the presence of conserved motifs and their phylogenetic relationship to other insect species. Moreover, FoccOBP3 was in silico characterized to analyse its structure along with molecular docking and molecular dynamics simulations to understand its binding with semiochemicals of F. occidentalis. Molecular docking revealed the interactions of methyl isonicotinate, p-anisaldehyde and (S)-(-)-verbenone with FoccOBP3. Moreover, molecular dynamics simulations showed bonding stability of these ligands with FoccOBP3, and field trials validated that Lurem TR (commercial product) and p-anisaldehyde had greater attraction as compared to (S)-(-)-verbenone, given the compound's binding with FoccOBP3. The current study helps in understanding the tertiary structure and interaction of FoccOBP3 with lures using computational and field data and will help in the identification of novel lures of insects in the future, given the importance of binding with OBPs.Communicated by Ramaswamy H. Sarma.

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.

Identification and expression profiles of olfactory-related genes based on transcriptome analysis in Plodia interpunctella (Lepidoptera: Pyralidae)

The sophisticated olfactory system of insects is plays a critical role in detecting chemical signals and guiding insect behaviors, such as selecting mates, finding hosts, evading predators, and discovering oviposition sites. Therefore, exploring and clarifying the molecular processes of this system is crucial for developing new insecticides or efficient pest control methods. Plodia interpunctella (Hübner) is a disruptive insect pest damaging the stored grains over the world. However, the olfactory processes of P. interpunctella remain unclear. Herein, we employed a transcriptome analysis to identify olfactory and differentially expressed genes to characterize their expression patterns in different developmental stages and antennal tissue. Subsequently, a total of 172 potential olfactory-related genes included 42 odorant-binding proteins, 12 chemosensory proteins, 51 odorant receptors, 13 gustatory receptors, three sensory neuron membrane proteins, and 51 ionotropic receptors. Furthermore, phylogenetic analysis and BLASTx best-hit analyses showed that these olfactory genes were closely linked with those identified in other lepidopterans. Transcriptome analysis revealed 49 differentially expressed olfactory-related genes, and a semiquantitative reverse transcription polymerase chain reaction showed that 11 olfactory genes were particularly expressed in the legs and wings of female P. interpunctella. Meanwhile, PintOBP29 was notably expressed in female antennae and legs. Genes with high expression levels in the abdomen showed high expression in the legs, but low expression in the antennae. Our findings provide the candidate genetic factors for analysis of the olfactory processes in P. interpunctella.

Comparative Transcriptomic Assessment of Chemosensory Genes in Adult and Larval Olfactory Organs of Cnaphalocrocis medinalis

The rice leaf folder, Cnaphalocrocis medinalis (Lepidoptera: Pyralidae), is a notorious pest of rice in Asia. The larvae and adults of C. medinalis utilize specialized chemosensory systems to adapt to different environmental odors and physiological behaviors. However, the differences in chemosensory genes between the olfactory organs of these two different developmental stages remain unclear. Here, we conducted a transcriptome analysis of larvae heads, male antennae, and female antennae in C. medinalis and identified 131 putative chemosensory genes, including 32 OBPs (8 novel OBPs), 23 CSPs (2 novel CSPs), 55 ORs (17 novel ORs), 19 IRs (5 novel IRs) and 2 SNMPs. Comparisons between larvae and adults of C. medinalis by transcriptome and RT-qPCR analysis revealed that the number and expression of chemosensory genes in larval heads were less than that of adult antennae. Only 17 chemosensory genes (7 OBPs and 10 CSPs) were specifically or preferentially expressed in the larval heads, while a total of 101 chemosensory genes (21 OBPs, 9 CSPs, 51 ORs, 18 IRs, and 2 SNMPs) were specifically or preferentially expressed in adult antennae. Our study found differences in chemosensory gene expression between larvae and adults, suggesting their specialized functions at different developmental stages of C. medinalis. These results provide a theoretical basis for screening chemosensory genes as potential molecular targets and developing novel management strategies to control C. medinalis.

Functional Characterization of Pheromone Receptors in the Beet Webworm, Loxostege sticticalis (Lepidoptera: Pyralidae)

Lepidopteran insects mainly rely on sex pheromones to complete sexual communications. Pheromone receptors (PRs) are expressed on the olfactory receptor neurons (ORNs) of the sensilla trichodea and play an essential role in sexual communication. Despite extensive investigations into the mechanisms of peripheral recognition of sex pheromones in Lepidoptera, knowledge about these mechanisms in L. sticticalis remains limited. In this study, five candidate LstiPRs were analyzed in a phylogenetic tree with those of other Lepidopteran insects. Electroantennography (EAG) assays showed that the major sex pheromone component E11-14:OAc elicited a stronger antennal response than other compounds in male moths. Moreover, two types of neurons in sensilla trichodea were classified by single sensillum recordings, of which the "a" neuron specifically responded to E11-14:OAc. Five candidate PRs were functionally assayed by the heterologous expression system of Xenopus oocytes, and LstiPR2 responded to the major sex pheromone E11-14:OAc. Our findings suggest that LstiPR2 is a PR sensitive to L. sticticalis's major sex pheromone compound, E11-14:OAc. Furthermore, this study offers valuable insights into the sexual communication behavior of L. sticticalis, forming a foundation for further analysis of the species' central nervous system.

Role of Genes in Regulating Host Plants Expansion in Tephritid Fruit Flies (Diptera) and Potential for RNAi-Based Control

Host plant expansion is an important survival strategy for tephritids as they expand their range. Successful host expansion requires tephritids to adapt to the chemical and nonchemical properties of a novel host fruit, such as fruit color, phenology, and phytochemicals. These plant properties trigger a series of processes in tephritids, with each process having its own genetic basis, which means that various genes are involved in regulating host plant expansion by tephritids. This review summarizes current knowledge on the categories and roles of genes involved in host plant expansion in several important tephritid species, including genes related to chemoreception (olfactory and gustation), vision, digestion, detoxification, development, ribosomal and energy metabolism. Chemoreception- and detoxification- and digestion-related genes are stimulated by volatile chemicals and secondary chemicals of different hosts, respectively, which are involved in the regulation of nervous signal transduction that triggers behavioral, physical, and chemical responses to the novel host fruit. Vision-, nerve-, and development-related genes and metabolism-associated genes are activated in response to nonchemical stimuli from different hosts, such as color and phenology, to regulate a comprehensive adaptation of the extending host for tephritids. The chemical and nonchemical signals of hosts activate ribosomal and energy-related genes that result in the basic regulation of many processes of host expansion, including detoxification and development. These genes do not regulate novel host use individually, but multiple genes regulate multilevel adaptation to novel host fruits via multiple mechanisms. These genes may also be potential target genes for RNAi-based control of tephritid pests.

Identification of Chemosensory Genes, Including Candidate Pheromone Receptors, in Phauda flammans (Walker) (Lepidoptera: Phaudidae) Through Transcriptomic Analyses

Olfactory and gustatory systems play an irreplaceable role in all cycles of growth of insects, such as host location, mating, and oviposition. Many chemosensory genes in many nocturnal moths have been identified via omics technology, but knowledge of these genes in diurnal moths is lacking. In our recent studies, we reported two sex pheromone compounds and three host plant volatiles that play a vital role in attracting the diurnal moth, Phauda flammans. The antennal full-length transcriptome sequence of P. flammans was obtained using the Pacbio sequencing to further explore the process of sex pheromone and host plant volatile recognition in P. flammans. Transcriptome analysis identified 166 candidate olfactory and gustatory genes, including 58 odorant-binding proteins (OBPs), 19 chemosensory proteins (CSPs), 59 olfactory receptors (ORs), 16 ionotropic receptors (IRs), 14 gustatory receptors (GRs), and 2 sensory neuron membrane proteins (SNMPs). Subsequently, a phylogenetic tree was established using P. flammans and other lepidopteran species to investigate orthologs. Among the 17 candidate pheromone receptor (PR) genes, the expression levels of PflaOR21, PflaOR25, PflaOR35, PflaOR40, PflaOR41, PflaOR42, PflaOR44, PflaOR49, PflaOR51, PflaOR61, and PflaOR63 in the antennae were significantly higher than those in other non-antennae tissues. Among these PR genes, PflaOR21, PflaOR27, PflaOR29, PflaOR35, PflaOR37, PflaOR40, PflaOR42, PflaOR44, PflaOR60, and PflaOR62 showed male-biased expression, whereas PflaOR49, PflaOR61, and PflaOR63 revealed female-biased expression. The functions of related OR genes were also discussed. This research filled the gap of the chemosensory genes of P. flammans and provided basic data for future functional molecular mechanisms studies on P. flammans olfaction.

Transcriptome Analysis and Characterization of Chemosensory Genes in the Forest Pest, Dioryctria abietella (Lepidoptera: Pyralidae)

In Lepidoptera, RNA sequencing has become a useful tool in identifying chemosensory genes from antennal transcriptomes, but little attention is paid to non-antennal tissues. Though the antennae are primarily responsible for olfaction, studies have found that a certain number of chemosensory genes are exclusively or highly expressed in the non-antennal tissues, such as proboscises, legs and abdomens. In this study, we report a global transcriptome of 16 tissues from Dioryctria abietella, including chemosensory and non-chemosensory tissues. Through Illumina sequencing, totally 952,658,466 clean reads were generated, summing to 142.90 gigabases of data. Based on the transcriptome, 235 chemosensory-related genes were identified, comprising 42 odorant binding proteins (OBPs), 23 chemosensory proteins (CSPs), 75 odorant receptors (ORs), 62 gustatory receptors (GRs), 30 ionotropic receptors (IRs), and 3 sensory neuron membrane proteins (SNMPs). Compared to a previous study in this species, 140 novel genes were found. A transcriptome-wide analysis combined with PCR results revealed that except for GRs, the majority of other five chemosensory gene families in Lepidoptera were expressed in the antennae, including 160 chemosensory genes in D. abietella. Using phylogenetic and expression profiling analyses, members of the six chemosensory gene repertoires were characterized, in which 11 DabiORs were candidates for detecting female sex pheromones in D. abietella, and DabiOR23 may be involved in the sensing of plant-derived phenylacetaldehyde. Intriguingly, more than half of the genes were detected in the proboscises, and one fourth of the genes were found to have the expression in the legs. Our study not only greatly extends and improves the description of chemosensory genes in D. abietella, but also identifies potential molecular targets involved in olfaction, gustation and non-chemosensory functions for control of this pest.

The microsporidium Nosema pyrausta as a potent microbial control agent of the beet webworm Loxostege sticticalis

The microsporidium Nosema pyrausta is an important mortality factor of the European corn borer, Ostrinia nubilalis. The present study was aimed at N. pyrausta virulence testing to the beet webworm (BW), Loxostege sticticalis. This agricultural pest, L. sticticalis, was highly vulnerable to N. pyrausta. The parasite's spores were located in salivary glands, adipose tissue, and Malpighian tubules of the infected specimens. Infection was transmitted transovarially through at least 3 laboratory generations, in which BW fitness indices were lower than in the control, and moth emergence and fertility decreased prominently. Transovarial infection was most detrimental to female egg-laying ability, resulting in zero fertility in F3. When propagated in BW, the microsporidium tended to increase its virulence to L. sticticalis, as compared to the Ostrinia isolates. The parasite's ability to infect this host at low dosages and transmit vertically should guarantee its effective establishment and spread within BW populations. In conclusion, N. pyrausta is a promising agent against BW, which is a notorious polyphagous pest in Eurasia.

Two classic OBPs modulate the responses of female Holotrichia oblita to three major ester host plant volatiles

Insects possess a fairly sophisticated olfactory system in their antennae to detect odorants essential for their survival and reproduction. Among them, insect first perceives odour sources by odorant-binding proteins (OBPs) to locate host-plants. Methyl salicylate, (Z)-3-hexenyl acetate and dibutyl phthalate are major volatile components of Ulmus pumila and Ricinus communis and elicit strong responses of the scarab beetle Holotrichia oblita adults. However, olfactory perception of the scarab beetle to these odorant compounds is unclear. In the current study, we cloned the OBP6 and OBP7 of H. oblita. The expression pattern shows that the two genes were highly expressed in the antennae of female beetles. Binding assays verified that the HoblOBP6 had a better binding affinity to methyl salicylate, and so did HoblOBP7 to (Z)-3-hexenyl acetate and dibutyl phthalate. The effect on the responses of female beetles to the three compounds was decreased significantly after these two genes were silenced by RNA interference. These results indicate that HoblOBP6 and HoblOBP7 are essential for female H. oblita perception of methyl salicylate, (Z)-3-hexenyl acetate and dibutyl phthalate. Our study provides important insights into the olfactory mechanism of female H. oblita to ester plant volatiles and could facilitate the development of potential pest control strategies in the field.

Identification and comparative expression analysis of odorant-binding proteins in the reproductive system and antennae of Athetis dissimilis

Odorant-binding proteins (OBPs) are prevalent in the antennal transcriptomes of different orders of insects. Studies on OBPs have focused on their role in the insect chemosensory system, but knowledge of their functions in the insect testis is limited. We sequenced the transcriptomes of the Athetis dissimilis reproductive organs and analyzed the expression of AdisOBP genes in different tissues. We identified 23 OBPs in the testis and ovaries and 31 OBPs in antennal transcriptomes. The results of real-time quantitative PCR revealed that 23 of the 54 OBP genes were highly expressed in both female and male antennae, including three that exhibited male-biased expression and 15 that exhibited female-biased expression. A total of 24 OBPs were highly expressed in the testis of A. dissimilis, while expression of OBPs in the ovaries was very low. These findings highlight the functional diversity of OBPs in insects and can facilitate further studies on the OBPs in A. dissimilis and lepidopteran species.

Transcriptome Characterization and Expression Analysis of Chemosensory Genes in Chilo sacchariphagus (Lepidoptera Crambidae), a Key Pest of Sugarcane

Insect chemoreception involves many families of genes, including odourant/pheromone binding proteins (OBP/PBPs), chemosensory proteins (CSPs), odourant receptors (ORs), ionotropic receptors (IRs), and sensory neuron membrane proteins (SNMPs), which play irreplaceable roles in mediating insect behaviors such as host location, foraging, mating, oviposition, and avoidance of danger. However, little is known about the molecular mechanism of olfactory reception in Chilo sacchariphagus, which is a major pest of sugarcane. A set of 72 candidate chemosensory genes, including 31 OBPs/PBPs, 15 CSPs, 11 ORs, 13 IRs, and two SNMPs, were identified in four transcriptomes from different tissues and genders of C. sacchariphagus. Phylogenetic analysis was conducted on gene families and paralogs from other model insect species. Quantitative real-time PCR (qRT-PCR) showed that most of these chemosensory genes exhibited antennae-biased expression, but some had high expression in bodies. Most of the identified chemosensory genes were likely involved in chemoreception. This study provides a molecular foundation for the function of chemosensory proteins, and an opportunity for understanding how C. sacchariphagus behaviors are mediated via chemical cues. This research might facilitate the discovery of novel strategies for pest management in agricultural ecosystems.

Contribution to the knowledge of the arthropods community inhabiting the winter-flooded meadows (marcite) of northern Italy

Background

Flooded semi-natural grasslands are endangered ecosystems throughout Europe. In Italy, amongst flooded meadows, one special type called "marcita" is strongly threatened. It is a stable flooded grassland used to produce green forage even during winter months due to the thermal properties of water coming from springs and fountains that prevent the soil from freezing. To date, some research has been carried out to investigate the role of the marcita for ornithological and herpetological communities. However, no comprehensive data on invertebrates inhabiting this particular biotope available. The aim of this study was to characterise the terrestrial entomological community of these typical winter-flooded meadows in northern Italy and, in particular, in six marcita fields located in the Ticino Valley Regional Park. We collected data on species richness and diversity of Carabidae, Staphylinidae, Araneae, Lepidoptera and Orthoptera inhabiting marcita during the summers of 2014 and 2015 and data on overwintering Coleoptera during the winter of 2014-2015. Amongst the collected species, we identified those highly linked to this habitat.

New information

We found a total of 47 ground beetle species, 35 rove beetle species, 29 spider species, one Lucanidae, 16 butterfly species and 24 grasshopper and cricket species. Most of the species were collected during the summers of 2014 and 2015, while some others were also, or exclusively, overwintering (17 ground beetles, four rove beetles and one Lucanidae) and were collected during the winter of 2014-2015.Marcita fields hosted specialised species and species typical of hygrophilous habitats, amongst which are included the butterfly Lycaena dispar, the ground beetle Dolichus halensis and the grasshopper Chrysochraon dispar. This study represents the first contribution to the knowledge of terrestrial arthropod communities associated with this particular type of winter-irrigated meadow in Europe and confirms the importance of this biotope for invertebrate conservation in agricultural landscapes.

The whole body transcriptome of Coleophora obducta reveals important olfactory proteins

Background

The tiny casebearer moth Coleophora obducta, an important defoliator of Larix spp., is a major threat to ecological security in north China. Studies have shown that C. obducta is strongly specific to host plants; it is unable complete its life cycle without Larix spp. The sex pheromones of C. obducta Z5-10:OH have been elucidated; and eight types of antennae sensilla, have been detected, indicating that an exploration of its olfactory proteins is necessary, due to the general lack of information on this topic.

Methods

We investigated the whole body transcriptome of C. obducta, performed a phylogenetic analysis of its olfactory proteins and produced expression profiles of three pheromone-binding proteins (CobdPBPs) by qRT–PCR.

Results

We identified 16 odorant binding proteins, 14 chemosensory proteins, three sensory neuron membrane proteins, six odorant degrading enzymes, five antennal esterases, 13 odorant receptors, seven ionotropic receptors and 10 gustatory receptors, including three PBPs and one odorant co-receptor. Additionally, three putative pheromone receptors, two bitter gustatory receptors and five functional ionotropic receptors were found by phylogenetic analysis. The expression profiles of three PBPs in males and females showed that all of them exhibited male-specific expression and two were expressed at significantly higher levels in males. These data provide a molecular foundation from which to explore the olfactory recognition process and may be useful in the development of a new integrated pest management strategy targeting olfactory recognition of C. obducta.

Molecular Characterization and Key Binding Sites of Sex Pheromone-Binding Proteins from the Meadow Moth, Loxostege sticticalis

The meadow moth, Loxostege sticticalis, is a typical agricultural pest that uses sex pheromones to mediate mating behavior; however, the mechanism underlying the selectivity of its pheromone-binding proteins (PBPs) remains unknown. In this study, LstiPBP1 and LstiPBP3 were cloned, expressed, and purified, and the fluorescence binding assay showed that LstiPBP1 binds to the major sex pheromone component, E-11-tetradecenol (E11-14:OH), with high affinity; moreover, E11-14:OH could evoke a significant antennal electrophysiological response and attract L. sticticalis males. After LstiPBP1 was silenced, both the antennal response and attractiveness of E11-14:OH decreased significantly. Molecular docking predicted that a hydrogen bonding site, Leu37, played key role in the binding of LstiPBP1 to E11-14:OH. After Leu37 was mutated, the E11-14:OH-binding affinity decreased drastically. These results suggest that LstiPBP1 participates in E11-14:OH recognition and could be used as a target gene to disturb the mating behavior of L. sticticalis and develop new odorants for pest control.

Comparative Genomics Reveals Thousands of Novel Chemosensory Genes and Massive Changes in Chemoreceptor Repertories across Chelicerates

Chemoreception is a widespread biological function that is essential for the survival, reproduction, and social communication of animals. Though the molecular mechanisms underlying chemoreception are relatively well known in insects, they are poorly studied in the other major arthropod lineages. Current availability of a number of chelicerate genomes constitutes a great opportunity to better characterize gene families involved in this important function in a lineage that emerged and colonized land independently of insects. At the same time, that offers new opportunities and challenges for the study of this interesting animal branch in many translational research areas. Here, we have performed a comprehensive comparative genomics study that explicitly considers the high fragmentation of available draft genomes and that for the first time included complete genome data that cover most of the chelicerate diversity. Our exhaustive searches exposed thousands of previously uncharacterized chemosensory sequences, most of them encoding members of the gustatory and ionotropic receptor families. The phylogenetic and gene turnover analyses of these sequences indicated that the whole-genome duplication events proposed for this subphylum would not explain the differences in the number of chemoreceptors observed across species. A constant and prolonged gene birth and death process, altered by episodic bursts of gene duplication yielding lineage-specific expansions, has contributed significantly to the extant chemosensory diversity in this group of animals. This study also provides valuable insights into the origin and functional diversification of other relevant chemosensory gene families different from receptors, such as odorant-binding proteins and other related molecules.

Identification of chemosensory genes from the antennal transcriptome of Indian meal moth Plodia interpunctella

Olfaction plays an indispensable role in mediating insect behavior, such as locating host plants, mating partners, and avoidance of toxins and predators. Olfactory-related proteins are required for olfactory perception of insects. However, very few olfactory-related genes have been reported in Plodia interpunctella up to now. In the present study, we sequenced the antennae transcriptome of P. interpunctella using the next-generation sequencing technology, and identified 117 candidate olfactory-related genes, including 29 odorant-binding proteins (OBPs), 15 chemosensory proteins (CSPs), three sensory neuron membrane proteins (SNMPs), 47 odorant receptors (ORs), 14 ionotropic receptors (IRs) and nine gustatory receptors (GRs). Further analysis of qRT-PCR revealed that nine OBPs, three CSPs, two SNMPs, nine ORs and two GRs were specifically expressed in the male antennae, whereas eight OBPs, six CSPs, one SNMP, 16 ORs, two GRs and seven IRs significantly expressed in the female antennae. Taken together, our results provided useful information for further functional studies on insect genes related to recognition of pheromone and odorant, which might be meaningful targets for pest management.

Antennal transcriptome analysis and expression profiles of olfactory genes in Anoplophora chinensis

Olfaction in insects is essential for host identification, mating and oviposition, in which olfactory proteins are responsible for chemical signaling. Here, we determined the transcriptomes of male and female adult antennae of Anoplophora chinensis, the citrus longhorned beetle. Among 59,357 unigenes in the antennal assembly, we identified 46 odorant-binding proteins, 16 chemosensory proteins (CSPs), 44 odorant receptors, 19 gustatory receptors, 23 ionotropic receptors, and 3 sensory neuron membrane proteins. Among CSPs, AchiCSP10 was predominantly expressed in antennae (compared with legs or maxillary palps), at a significantly higher level in males than in females, suggesting that AchiCSP10 has a role in reception of female sex pheromones. Many highly expressed genes encoding CSPs are orthologue genes of A. chinensis and Anoplophora glabripennis. Notably, AchiPBP1 and AchiPBP2 showed 100% and 96% identity with AglaPBP1 and AglaPBP2 from A. glabripennis, with similar expression profiles in the two species; PBP2 was highly expressed in male antennae, whereas PBP1 was expressed in all three tissues in both males and females. These results provide a basis for further studies on the molecular chemoreception mechanisms of A. chinensis, and suggest novel targets for control of A. chinensis.