Asian corn borer pheromone binding protein 3, a candidate for evolving specificity to the 12-tetradecenyl acetate sex pheromone

Morphological and genetic differences in legs of a polygamous beetle between sexes, Glenea cantor (Coleopter: Cerambycidae: Lamiinae)

The legs of insects play an important role in their daily behaviour, especially reproduction. Entomologists have performed much research on the role of the leg in different behaviours of beetles, an important group in the insect family, but relatively little has been done to study the ultrastructure and transcriptome of their legs. Hence, we systematically studied the ultrastructure and gene expression of the leg of G. cantor, a polygynous beetle, and compared its male and female diversity. In this study, we found the fore-leg, mid-leg and hind-leg of the female were significantly longer than those of the male. From the perspective of intuitive structural differences, we also compared the ultrastructures of the adhesion structure (tarsal) of males and females. The tarsal functional structure of the adult leg mainly includes sensilla and an adhesion structure. The sensilla on the tarsal joint mainly include sensilla chaetica (SCh II, SCh III) and sensilla trichodea (ST II). The adhesion structure includes disc-shaped bristles (di), lanceolate bristles (la), serrated bristles (se), spatula-shaped bristles (spl) and mushroom-shaped bristles (mus). Although there was no significant difference in sensillum distribution or type between males and females, there were significant differences in the distribution and species of adhesion structures between the fore-leg, mid-leg, and hind-leg of the same sex and between males and females. Therefore, different adhesion structures play different roles in various behaviours of beetles. On the other hand, the transcriptome results of male and female legs were screened for a subset of olfaction- and mechanics-related genes. We discovered that the male leg showed upregulation of 1 odorant binding protein (OBP), 2 Olfactory receptors (ORs) and 2 Chemosensory proteins (CSPs). Meanwhile, the female leg showed upregulation of 3 OBPs, 1 OR, 1 Gustatory receptor (GR) and 3 Mechanosensitive proteins (MSPs). An in-depth examination of the ultrastructure and molecular composition of the legs can elucidate its function in the reproductive behavior of G. cantor. Moremore, this investigation will serve as a cornerstone for subsequent research into the underlying behavioral mechanisms.

Current understandings of olfactory molecular events in the Asian corn borer, Ostrinia furnacalis (Lepidoptera: Crambidae)

The Asian corn borer Ostrinia furnacalis (Lepidoptera: Crambidae) is a serious corn pest with widespread distribution in East Asia. Its olfactory mechanism is a focus of scientific study, aiming to find good ways to control this pest. Molecular events are considered to be important in olfactory mechanism. Current understandings of olfactory molecular events in O. furnacalis, mainly involving sex pheromones and olfactory proteins, were summarized to provide a reference for further studies. O. furnacalis sex pheromone contains two components E-12-tetradecenyl acetate and Z-12-tetradecenyl acetate, which may be recognized and bound by the pheromone binding proteins OfurPBP3 and OfurPBP2, and then transported to the odorant receptors (ORs) OfurOR4 and OfurOR6 to activate them. The ORs OfurOR8, OfurOR7 and OfurOR5b mainly respond to the sex pheromone components of other Ostrinia species, E-11-tetradecenyl acetate, Z-11-tetradecenyl acetate and Z-9-tetradecenyl acetate. The OR OfurOR27 responds strongly to plant odorants nonanal, octanal and 1-octanol. Much work remains to be done to fully understand odorants with olfactory activity to O. furnacalis and the functions of its olfactory proteins. These studies will help to reveal olfactory mechanism in O. furnacalis, with the aim of regulating its behaviors to control this pest.

Expression profile and functional characterization of odorant binding proteins in a forest pest, Dioryctria abietella (Lepidoptera: Pyralidae)

In the forest ecosystem dominated by the Pinaceae plants, this boring pest Dioryctria abietella is subject to a variety of odorants derived from host and nonhost plants, in which olfactory-related proteins enriched in antennae are key behavioral modulators for the orientation of feeding and ovipositing hosts. Here, we addressed the odorant binding protein (OBP) gene family in D. abietella. Expression profiles revealed that the majority of OBPs were abundantly expressed in the antennae at a female-biased level. A male-antenna-biased DabiPBP1 was a strong candidate for detecting type I and type II pheromones of D. abitella female moths. Using a prokaryotic expression system combined with affinity chromatography, we harvested two antenna-dominant DabiOBPs. In the ligand-binding assays, the two DabiOBPs exhibited different odorant response spectra, as DabiOBP17 was tuned to most odorants with higher affinities compared to DabiOBP4. Of these, DabiOBP4 could strongly bind syringaldehyde and citral (dissociation constants (K_i) < 14 μM). A floral volatile, benzyl benzoate (K_i = 4.72 ± 0.20 μM), was the best ligand for DabiOBP17. Remarkably, several green leaf volatiles were found to strongly interact with DabiOBP17 (K_i < 8.5 μM), including Z3-hexenyl acetate, E2-hexenol, Z2-hexenal and E2-hexenal that may mediate a repellent response to D. abietella. Structural analyses of ligands revealed that the binding of the two DabiOBPs to odorants was associated with carbon-chain lengths and functional groups. Molecular simulations identified several key residues involved in the interactions of DabiOBPs and ligands, suggesting specific binding mechanisms. This study highlights olfactory roles of two antennal DabiOBPs in D. abietella, helping the identification of potentially behavioral compounds for the population control of this pest.

Identification and expression profile analysis of chemosensory genes in pine needle gall midge, Thecodiplosis japonensis (Diptera: Cecidomyiidae)

Insects have highly specialized and sensitive olfactory systems involving several chemosensory genes to locate their mates and hosts or escape from predators. Pine needle gall midge, Thecodiplosis japonensis (Diptera: Cecidomyiidae), has invaded China since 2016 and caused serious damage. Till now, there is no environmentally friendly measure to control this gall midge. Screening molecules with high affinity to target odorant-binding protein to develop highly efficient attractants is a potential pest management method. However, the chemosensory genes in T. japonensis are still unclear. We identified 67 chemosensory-related genes in the transcriptomes of antennae, including 26 OBPs, 2 CSPs, 17 ORs, 3 SNMPs, 6 GRs, and 13 IRs, using high throughput sequencing. Phylogenetic analysis of these six chemosensory gene families among Dipteran was performed to classify and predict the functions. The expression profiles of OBPs, CSPs and ORs were validated by quantitative real-time PCR. 16 of the 26 OBPs were biased expressed in antennae. TjapORco and TjapOR5 were highly expressed in the antenna of unmated male and female adults. The functions of related OBPs and ORs genes were also discussed. These results provide a basis for the functional research on chemosensory genes at the molecular level.

Ostrinia furnacalis PBP2 solution NMR structure: Insight into ligand binding and release mechanisms

Ostrinia furnacalis is an invasive lepidopteran agricultural pest that relies on olfaction for mating and reproduction. Male moths have an extremely sensitive olfactory system that can detect the sex pheromones emitted by females over a great distance. Pheromone-binding proteins present in the male moth antenna play a key role in the pheromone uptake, transport, and release at the dendritic membrane of the olfactory neuron. Here, we report the first high-resolution NMR structure of a pheromone-binding protein from an Ostrinia species at pH 6.5. The core of the Ostrinia furnacalis PBP2 (OfurPBP2) consists of six helices, α1a (2-14), α1b (16-22), α2 (27-37), α3 (46-60), α4 (70-80), α5 (84-100), and α6 (107-124) surrounding a large hydrophobic pocket. The structure is stabilized by three disulfide bridges, 19-54, 50-108, and 97-117. In contrast to the unstructured C-terminus of other lepidopteran PBPs, the C-terminus of OfurPBP2 folds into an α-helix (α7) at pH 6.5. The protein has nanomolar affinity towards both pheromone isomers. Molecular docking of both pheromones, E-12 and Z-12-tetradecenyl acetate, to OfurPBP2 revealed that the residues Met5, Lys6, Met8, Thr9, Phe12, Phe36, Trp37, Phe76, Ser115, Phe118, Lys119, Ile122, His123, and Ala128 interact with both isomers, while Thr9 formed a hydrogen bond with the acetate head group. NMR structure and thermal unfolding studies with CD suggest that ligand release at pH 4.5 is likely due to the partial unfolding of the protein.

Functional differentiation of three pheromone binding proteins in Orthaga achatina using mixed-type sex pheromones

Pheromone-binding proteins (PBPs) play important roles in perception of insect sex pheromones, functioning to recognize and transport pheromone components onto the olfactory receptors of the odorant sensing neurons. Orthaga achatina, a serious pest of camphor trees, uses a mixture of three Type I (Z11-16:OAc, Z11-16:OH and Z11-16:Ald) and one Type II (Z3,Z6,Z9,Z12,Z15-23:H) sex pheromone components in its sex communication, in which Z11-16:OAc is the major component and others are minor components. In this study, we for the first time demonstrated that the three PBPs differentiated in recognition among pheromone components in a moth using mixed-type sex pheromones. First, tissue expression study showed that all three PBPs of O. achatina were expressed only in antennae and highly male-biased, suggesting their involvement in perception of the sex pheromones. Second, the three PBPs were expressed in Escherichia coli and the binding affinities of PBPs to four sex pheromone components and some pheromone analogs were determined by the fluorescence competition binding assays. The results showed that OachPBP1 bound all four sex pheromone components with high binding affinity, while OachPBP2 had high or moderate binding affinity only to three Type I components, and OachPBP3 had high binding affinity only to three minor pheromone components. Furthermore, key amino acid residues that bind to sex pheromone components were identified in three PBPs by 3-D structure modeling and ligand molecular docking, predicting the interactions between PBPs and pheromone components. Our study provides a fundamental insight into the olfactory mechanism in moths that use mixed-type sex pheromones.

Structural and Functional Characterization of European Corn Borer, Ostrinia nubilalis, Pheromone Binding Protein 3

Ostrinia nubilalis, a lepidopteran moth, also known as the European corn borer, has a major impact on the production of economically important crops in the United States and Europe. The female moth invites the male moth for mating through the release of pheromones, a volatile chemical signal. Pheromone binding proteins (PBPs) present in the male moth antennae are believed to pick up the pheromones, transport them across the aqueous sensillum lymph, and deliver them to the olfactory receptor neurons. Here we report for the first time the cloning, expression, refolding, purification, and structural characterization of Ostrinia nubilalis PBP3 (OnubPBP3). The recombinant protein showed nanomolar affinity to each isomer of the Ostrinia pheromones, E- and Z-11-tetradecenyl acetate. In a pH titration study by nuclear magnetic resonance, the protein exhibited an acid-induced unfolding at pH below 5.5. The molecular dynamics simulation study demonstrated ligand-induced conformational changes in the protein with both E- and Z-isomers of the Ostrinia pheromone. The simulation studies showed that while protein flexibility decreases upon binding to E-pheromone, it increases when bound to Z-pheromone. This finding suggests that the OnubPBP3 complex with E-pheromone is more stable than with Z-pheromone.

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.

Insights into chemosensory genes of Pagiophloeus tsushimanus adults using transcriptome and qRT-PCR analysis

Pagiophloeus tsushimanus is a new, destructive, and monophagous weevil pest that thrives on Cinnamomum camphora, found in Shanghai. The functions of chemosensory genes involved in the host location and intraspecific communication of P. tsushimanus remain unknown. The male-female transcriptomes of P. tsushimanus adults were assembled using Illumina sequencing, and we focused on all chemosensory genes in transcriptomes. In general, 58,088 unigenes with a mean length of 1018.19 bp were obtained. In total, 39 odorant binding proteins (OBPs), 10 chemosensory proteins (CSPs), 22 olfactory receptors (ORs), 16 gustatory receptors (GRs), eight ionotropic receptors (IRs), and five sensory neuron membrane proteins (SNMPs) were identified. PtsuOBPs comprised four subfamilies (20 Minus-C, one Plus-C, two Dimer, and 15 Classic). Both PtsuOBPs and PtsuCSPs contained a highly conserved sequence motif of cysteine residues. PtsuORs including one olfactory receptor co-receptors (Ptsu/Orco) comprised seven predicted transmembrane domains. Phylogenetic analysis revealed that PtsuOBPs, PtsuCSPs, and PtsuORs in P. tsushimanus exhibited low homology compared to other insect species. The results of tissue- and sex-specific expression patterns indicated that PtsuOBPs and PtsuORs were highly abundant in the antennae; whereas, PtsuCSPs were not only highly abundant in antennae, but also abdominal apexes, wings, and legs. In conclusion, these results enrich the gene database of P. tsushimanus, which may serve as a basis for identifying novel targets to disrupt olfactory key genes and may provide a reverse validation method to identify attractants for formulating potential eco-friendly control strategies for this pest.

Odorant-binding proteins involved in sex pheromone and host-plant recognition of the sugarcane borer Chilo infuscatellus (Lepidoptera: Crambidae)

BACKGROUND

Pheromone-binding proteins (PBPs) are responsible for transporting sex pheromones and general odorant-binding proteins (GOBPs) have been proposed to transport host-plant volatiles. A large number of OBPs have been identified from Lepidoptera species. However, olfactory molecular biology and physiology studies on PBP and GOBP in sugarcane pests are limited. Chilo infuscatellus is one of the most widely distributed pests in sugarcane-producing areas.

RESULTS

Three PBPs (CinfPBP1, CinfPBP2 and CinfPBP3) and two GOBPs (CinfGOBP1 and CinfGOBP2) were identified, and five olfactory gene transcripts were abundantly expressed in antennae of C. infuscatellus. Binding assays showed that CinfPBP1-3 exhibited strong binding affinity for the sex pheromone components Z11-16:OH and 16:OH of C. infuscatellus. Meanwhile, CinfGOBP1-2 had high binding affinity with host-plant volatiles from sugarcane (Saccharum officinarum). Field-trapping results suggested that four volatile components, octadecane, (Z)-3-hexen-1-ol, α-terpineol and hexadecane from host plants and sex pheromone mixed baits have synergistic roles in attracting C. infuscatellus adult moths.

CONCLUSION

Functional characterization of CinfPBPs and CinfGOBPs in C. infuscatellus could help us find new environmentally friendly alternatives to conventional pest control using pesticides in sugarcane fields. © 2020 Society of Chemical Industry.

Identification of olfactory genes of a forensically important blow fly, Aldrichina grahami (Diptera: Calliphoridae)

Background

The time-length between the first colonization of necrophagous insect on the corpse and the beginning of investigation represents the most important forensic concept of minimum post-mortem inference (PMImin). Before colonization, the time spent by an insect to detect and locate a corpse could significantly influence the PMImin estimation. The olfactory system plays an important role in insect food foraging behavior. Proteins like odorant binding proteins (OBPs), chemosensory proteins (CSPs), odorant receptors (ORs), ionotropic receptors (IRs) and sensory neuron membrane proteins (SNMPs) represent the most important parts of this system. Exploration of the above genes and their necrophagous products should facilitate not only the understanding of their roles in forging but also their influence on the period before PMImin. Transcriptome sequencing has been wildly utilized to reveal the expression of particular genes under different temporal and spatial condition in a high throughput way. In this study, transcriptomic study was implemented on antennae of adult Aldrichina grahami (Aldrich) (Diptera: Calliphoridae), a necrophagous insect with forensic significance, to reveal the composition and expression feature of OBPs, CSPs, ORs, IRs and SNMPs genes at transcriptome level.

Method

Antennae transcriptome sequencing of A. grahami was performed using next-generation deep sequencing on the platform of BGISEQ-500. The raw data were deposited into NCBI (PRJNA513084). All the transcripts were functionally annotated using Gene Ontology (GO) and the Kyoto Encyclopedia of Genes and Genomes (KEGG) database. Differentially expressed genes (DEGs) were analyzed between female and male antennae. The transcripts of OBPs, CSPs, ORs, IRs and SNMPs were identified based on sequence feature. Phylogenetic development of olfactory genes of A. grahami with other species was analyzed using MEGA 5.0. RT-qPCR was utilized to verify gene expression generated from the transcriptome sequencing.

Results

In total, 14,193 genes were annotated in the antennae transcriptome based on the GO and the KEGG databases. We found that 740 DEGs were differently expressed between female and male antennae. Among those, 195 transcripts were annotated as candidate olfactory genes then checked by sequence feature. Of these, 27 OBPs, one CSPs, 49 ORs, six IRs and two SNMPs were finally identified in antennae of A. grahami. Phylogenetic development suggested that some olfactory genes may play a role in food forging, perception of pheromone and decomposing odors.

Conclusion

Overall, our results suggest the existence of gender and spatial expression differences in olfactory genes from antennae of A. grahami. Such differences are likely to greatly influence insect behavior around a corpse. In addition, candidate olfactory genes with predicted function provide valuable information for further studies of the molecular mechanisms of olfactory detection of forensically important fly species and thus deepen our understanding of the period before PMImin.

Field evaluation of sex pheromones and binding specificity of pheromone binding protein 4 in Tryporyza intacta (Lepidoptera: Crambidae)

The recognition of chemical signal including volatile odorants and pheromones is very important in the olfactory physiological behaviors of insects, such as avoiding predators, seeking food and mating partners. The sugarcane borer, Tryporyza intacta is the most harmful insect in sugarcane region in Southeast Asia and Southern China, however, the study of their molecular biology and physiology was limited. Here we demonstrated that the sex pheromone (E11-16:Ald: Z11-16:Ald = 7:3) were most effective to T. intacta. In addition, compared the traditional rubber lure, a new microsphere formulation lure can optimize the trapping effect and might be widely used in the sugarcane growing area. To obtain a better understanding of the olfactory molecular mechanism of pheromone-based mate recognition system, we have cloned the full-length gene of the TintPBP4 and expressed in Escherichia coli. Our phylogenetic analysis highlighted that the TintPBP4 was highly conserved among diverse species of Lepidoptera. Furthermore, the results of QRT-PCR demonstrated that TintPBP4 transcripts were abundantly expressed in the antennae of T. intacta, especially in the male adults. The fluorescence binding experiments showed the TintPBP4 exhibited strong binding capacities to the sex pheromone components. These results will not only provide more understanding for the functional analysis of olfactory proteins from T. intacta, but also assist in the exploitation and development of sex pheromones in the integrated biological control of this pest.

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.

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.

Mutations in pheromone-binding protein3 contribute to pheromone response variations in Plutella xylostella (L.) (Lepidoptera: Plutellidae)

BACKGROUND

Diamondback moth Plutella xylostella (L.) (Lepidoptera: Plutellidae) is one of the most important crucifer pests. Commercial sex attractants have been developed to monitor and control P. xylostella. However, some studies have demonstrated a variety of pheromone responses of P. xylostella in different locations of the world. Soluble pheromone-binding proteins (PBPs), as a subfamily of odorant-binding proteins (OBPs), could selectively bind and transport pheromones across aqueous sensillar lymph to the surface of olfactory receptor neurons. It is worthy to study whether the mutation of PxylPBPs is one of the reasons for the different responses of sex attractors in different regions.

RESULTS

In this study, P. xylostella males were collected from seven Chinese provinces, including Hainan, Guangdong, Yunnan, Fujian, Hunan, Zhejiang, and Hebei. PxylPBP1, PxylPBP2, and PxylPBP3 were cloned, and 3, 6, and 32 types of mutation pattern were identified, respectively. These mutation patterns were distributed in each province with different frequency. The results of fluorescence displacement binding assay and in silico simulation revealed that the three mutant PxylPBP3 were more sensitive to Z11-16:Ald than the reference protein (ACI28451).

CONCLUSION

This result implied that mutation of PxylPBP3 may have contributed to regional differences in pheromone responses of P. xylostella. © 2019 Society of Chemical Industry.

Antennal transcriptome analysis and expression profiles of odorant binding proteins in Clostera restitura

Clostera restitura Walker (Lepidoptera: Notodontidae) is one of the most destructive defoliators of poplars in China. We constructed an antennal transcriptome using Illumina Hiseq 2500™ sequencing and characterized the expression profiles of odorant binding proteins for better understanding of the olfactory receptive system and the role of putative olfactory proteins in C. restitura. A total of 165 transcripts were identified, including 43 transcripts encoding putative odorant-binding proteins (OBPs), 13 chemosensory proteins (CSPs), 78 odorant receptors (ORs), 15 ionotropic receptors (IRs), 13 gustatory receptors (GRs), and 3 sensory neuron membrane proteins (SNMPs). Furthermore, we systematically analyzed expression patterns of eight OBPs from different tissues of both C. restitura sexes by using reverse transcription PCR and quantitative real time PCR (RT-qPCR). The expression level of CresGOBP2 in female antennae was approximately two times higher than in males, and two pheromone binding proteins PBPs (CresPBP1 and -PBP3) and three OBPs (CresOBP9, -10, and -16) were more highly enriched in male antennae than in female antennae. CresOBP10 showed a remarkably high expression in legs compared to other studied insects. Our results suggested that these proteins might play a key role in foraging, seeking mates, and host recognition in C. restitura. Our findings provided a foundation for future studies on the molecular mechanisms controlling the olfactory system in C. restitura and potential novel targets for pest control strategies.

Structure and Function Studies of Asian Corn Borer Ostrinia furnacalis Pheromone Binding Protein2

Lepidopteran male moths have an extraordinarily sensitive olfactory system that is capable of detecting and responding to minute amounts of female-secreted pheromones over great distances. Pheromone-binding proteins (PBPs) in male antennae ferry the hydrophobic ligand across the aqueous lymph to the olfactory receptor neuron triggering the response. PBPs bind ligands at physiological pH of the lymph and release them at acidic pH near the receptor while undergoing a conformational change. In Anthereae polyphemus PBP1, ligand binding to the hydrophobic pocket and its release is regulated by two biological gates: His70 and His95 at one end of the pocket and C-terminus tail at the other end. Interestingly, in Asian corn borer Ostrinia furnacalis PBP2 (OfurPBP2), critical residues for ligand binding and release are substituted in both biological gates. The impact of these substitutions on the ligand binding and release mechanism in OfurPBP2 is not known. We report here overexpression of soluble OfurPBP2 and structural characterization at high and low pH by circular dichroism (CD) and NMR. Ligand binding and ab initio model development were carried out with fluorescence and small-angle X-ray scattering (SAXS) respectively. OfurPBP2 in solution at pH 6.5 is homogeneous, well-folded and has a compact globular shape.

Conservation and lineage-specific rearrangements in the GOBP/PBP gene complex of distantly related ditrysian Lepidoptera

General odorant binding proteins (GOBPs) and pheromone binding proteins (PBPs) form a monophyletic subfamily of insect odorant binding proteins (OBPs) specific for Lepidoptera, butterflies and moths. The GOBP/PBP genes include six subgroups (GOBP1–2, PBP-A–D) previously reported to form a complex arrayed in a conserved order in representative moths (superfamily Bombycoidea) and butterflies (Nymphalidae). Although our knowledge of lepidopteran genomes has increased greatly recently, the structure of the GOBP/PBP complex has been studied only for species that represent limited lineages of the highly diverged Ditrysia. To understand the evolution of this functionally important gene complex, we determined 69–149 kb genomic sequences that include GOBP2 and five PBP genes in three Ostrinia moths (Pyraloidea), O. nubilalis, O. furnacalis, and O. latipennis, using bacterial artificial chromosome (BAC) and fosmid clones. The structure of the GOBP2/PBP gene cluster was well conserved despite the different sex pheromone composition utilized by the three moths. Five expressed PBP genes in Ostrinia moths were the result of two duplications of PBP-A genes. Surprisingly, an allele containing a fusion gene between tandemly arrayed PBP-A genes was observed in O. nubilalis. We also revealed duplication and intra-chromosomal translocation of the GOBP1 gene in P. xylostella by fluorescence in situ hybridization (FISH) analysis. Additionally, we compared the structure of the GOBP/PBP gene complex of seventeen species covering six superfamilies and twelve families of the lepidopteran clade, Ditrysia, and found the gene order was basically conserved despite the frequent occurrence of lineage-specific gains, losses, inversions and translocations of these genes, compared with their neighboring genes. Our findings support the hypothesis that the structure of the GOBP/PBP gene complex was already established in the common ancestor of Ditrysia.

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

Loxostege sticticalis Linnaeus is an economically important agricultural pest, and the larvae cause great damage to crops, especially in Northern China. However, effective and environmentally friendly chemical methods for controlling this pest have not been discovered to date. In the present study, we performed HiSeq2500 sequencing of transcriptomes of the male and female adult antennae, adult legs and third instar larvae, and we identified 54 candidate odorant receptors (ORs), including 1 odorant receptor coreceptor (Orco) and 5 pheromone receptors (PRs), 18 ionotropic receptors (IRs), 13 gustatory receptors (GRs), 34 odorant binding proteins (OBPs), including 1 general odorant binding protein (GOBP1) and 3 pheromone binding proteins (PBPs), 10 chemosensory proteins (CSPs) and 2 sensory neuron membrane proteins (SNMPs). The results of RNA-Seq and RT-qPCR analyses showed the expression levels of most genes in the antennae were higher than that in the legs and larvae. Furthermore, PR4, OR1-4, 7–11, 13–15, 23, 29–32, 34, 41, 43, 47/IR7d.2/GR5b, 45, 7/PBP2-3, GOBP1, OBP3, 8 showed female antennae-biased expression, while PR1/OBP2, 7/IR75d/CSP2 showed male antennae-biased expression. However, IR1, 7d.3, 68a/OBP11, 20–22, 28/CSP9 had larvae enriched expression, and OBP15, 17, 25, 29/CSP5 were mainly expressed in the legs. The results shown above indicated that these genes might play a key role in foraging, seeking mates and host recognition in the L. sticticalis. Our findings will provide the basic knowledge for further studies on the molecular mechanisms of the olfactory system of L. sticticalis and potential novel targets for pest control strategies.

Binding affinity of five PBPs to Ostrinia sex pheromones

Background

Pheromone binding proteins (PBPs) of male Lepidoptera function in chemical communication, mate attraction and recognition. Directional selection was previously predicted between PBP3 orthologs of Ostrinia furnacalis and Ostrinia nubilalis were interpreted as being involved in sexual isolation.

Results

In vitro assays show that recombinant male OfurPBP3 bound O. furnacalis sex pheromones, Z-12-tetradecenyl acetate (Z12-14:OAc) and E-12-tetradecenyl acetate (E12-14:OAc), as well as to ECB pheromones Z11- and E11-14:OAc. Recombinant OfurPBP4 and OfurPBP5 bound E11- and Z11-14:OAc with greater affinity compared to Z12- and E12-14:OAc, and OfurPBP4 incapable of binding with E12-14:OAc. In silico molecular docking predicted OfurPBP3 residues Phe12, Ile52, Leu94, Ile113 within a hydrophobic ligand-binding pocket and may participate in E12- and Z12-14:OAc binding. Independent site-directed mutagenesis experiments demonstrated that Ser12, Asn52, Arg94, and Asn113 residues variants caused an approximately 1.7- to 4.6-fold reduction in OfurPBP3 affinity for Z12- and E12-14:OAc, and a 2.7- to 8.4-fold decrease in affinity towards E11- and Z11-14:OAc.

Conclusions

Five PBPs of O. furnacalis play important functions in Ostrinia pheromones binding. These four amino acids may play a role in binding of sex pheromone, but this study does not address questions regarding specific response between males of O. furnacalis and O. nubilalis. Additional studies are required determine the role, if any, PBPs play in the evolution of sex pheromone communication.

Electronic supplementary material

The online version of this article (doi:10.1186/s12867-017-0079-y) contains supplementary material, which is available to authorized users.

Functional characterization of a pheromone-binding protein from rice leaffolder Cnaphalocrocis medinalis in detecting pheromones and host plant volatiles

Pheromone-binding proteins (PBPs) are believed to be involved in the recognition of semiochemicals. In the present study, western blot analysis, fluorescence-binding characteristics and immunolocalization of CmedPBP4 from the rice leaffolder, Cnaphalocrocis medinalis, were investigated. Western blot analysis revealed that CmedPBP4 showed obvious antenna-specific expression patterns in female and male antenna, and made a clearly different sex-biased expression. Immunocytochemical labeling revealed that CmedPBP4 showed specific expression in the trichoid sensilla. Competitive fluorescence binding assays indicated that CmedPBP4 could selectively recognize three sex pheromone components (Z13-18:Ac, Z11-16:Al and Z13-18:OH) and eleven rice plant volatiles, including cyclohexanol, nerolidol, cedrol, dodecanal, ionone, (-)-α-cedrene, (Z)-farnesene, β-myrcene, R-(+)-limonene, (-)-limonene, and (+)-3-carene. Meanwhile the CmedPBP4 detection of sex pheromones and host odorants was pH-dependent. Our results, for the first time, provide further evidence that trichoid sensilla might be play an important role in detecting sex pheromones and host plant volatiles in the C. medinalis moth. Our systematic studies provided further detailed evidence for the function of trichoid sensilla in insect semiochemical perception.

Transcriptome Comparison Analysis of Ostrinia furnacalis in Four Developmental Stages

The Asian corn borer, Ostrinia furnacalis, is one of the most destructive pests of maize and causes huge losses in maize yield each year. In order to characterize the different developmental stages, a high-throughput sequencing platform was employed to perform de novo transcriptome assembly and gene expression analysis for the egg, larva, pupa and adult stages. Approximately 185 million reads were obtained, trimmed, and assembled into 42,638 unigenes with an average length of 801.94 bp and an N50 length of 1,152 bp. These unigene sequences were annotated and classified by performing Gene Ontology (GO), Cluster of Orthologous Groups (KOG) and Kyoto Encyclopedia of Genes and Genomes (KEGG) functional classifications. Comparison of the gene expression profiles of the two transitional stages revealed dramatic differences. Some differentially expressed genes are associated with digestion, cuticularization olfactory recognition and wing formation as well as growth and development. In total, 12 putative insect development-related genes were identified. Real-time quantitative PCR (RT-qPCR) results and sequencing based on relative expression levels of randomly selected genes confirmed these expression patterns. These data represent the most comprehensive transcriptomic resource currently available for O. furnacalis and will facilitate the study of developmental pathways, cuticularization, wing formation and olfactory recognition.

Sex pheromone recognition and characterization of three pheromone-binding proteins in the legume pod borer, Maruca vitrata Fabricius (Lepidoptera: Crambidae)

Pheromone-binding proteins (PBPs) are essential for the filtering, binding and transporting of sex pheromones across sensillum lymph to membrane-associated pheromone receptors of moths. In this study, three novel PBP genes were expressed in Escherichia coli to examine their involvement in the sex pheromone perception of Maruca vitrata. Fluorescence binding experiments indicated that MvitPBP1-3 had strong binding affinities with four sex pheromones. Moreover, molecular docking results demonstrated that six amino acid residues of three MvitPBPs were involved in the binding of the sex pheromones. These results suggested that MvitPBP1-3 might play critical roles in the perception of female sex pheromones. Additionally, the binding capacity of MvitPBP3 with the host-plant floral volatiles was high and was similar to that of MvitGOBP2. Furthermore, sequence alignment and docking analysis showed that both MvitGOBP2 and MvitPBP3 possessed an identical key binding site (arginine, R130/R140) and a similar protein pocket structure around the binding cavity. Therefore, we hypothesized that MvitPBP3 and MvitGOBP2 might have synergistic roles in binding different volatile ligands. In combination, the use of synthetic sex pheromones and floral volatiles from host-plant may be used in the exploration for more efficient monitoring and integrated management strategies for the legume pod borer in the field.

Male- and Female-Biased Gene Expression of Olfactory-Related Genes in the Antennae of Asian Corn Borer, Ostrinia furnacalis (Guenée) (Lepidoptera: Crambidae)

The Asian corn borer (ACB), Ostrinia furnacalis (Guenée), is a destructive pest insect of cultivated corn crops, for which antennal-expressed receptors are important to detect olfactory cues for mate attraction and oviposition. Few olfactory related genes were reported in ACB, so we sequenced and characterized the transcriptome of male and female O. furnacalis antennae. Non-normalized male and female O. furnacalis antennal cDNA libraries were sequenced on the Illumina HiSeq 2000 and assembled into a reference transcriptome. Functional gene annotations identified putative olfactory-related genes; 56 odorant receptors (ORs), 23 odorant binding proteins (OBPs), and 10 CSPs. RNA-seq estimates of gene expression respectively showed up- and down-regulation of 79 and 30 genes in female compared to male antennae, which included up-regulation of 8 ORs and 1 PBP gene in male antennae as well as 3 ORs in female antennae. Quantitative real-time RT-PCR analyses validated strong male antennal-biased expression of OfurOR3, 4, 6, 7, 8, 11, 12, 13 and 14 transcripts, whereas OfurOR17 and 18 were specially expressed in female antennae. Sex-biases gene expression described here provides important insight in gene functionalization, and provides candidate genes putatively involved in environmental perception, host plant attraction, and mate recognition.

Antennal Transcriptome Analysis of Odorant Reception Genes in the Red Turpentine Beetle (RTB), Dendroctonus valens

BACKGROUND

The red turpentine beetle (RTB), Dendroctonus valens LeConte (Coleoptera: Curculionidae, Scolytinae), is a destructive invasive pest of conifers which has become the second most important forest pest nationwide in China. Dendroctonus valens is known to use host odors and aggregation pheromones, as well as non-host volatiles, in host location and mass-attack modulation, and thus antennal olfaction is of the utmost importance for the beetles' survival and fitness. However, information on the genes underlying olfaction has been lacking in D. valens. Here, we report the antennal transcriptome of D. valens from next-generation sequencing, with the goal of identifying the olfaction gene repertoire that is involved in D. valens odor-processing.

RESULTS

We obtained 51 million reads that were assembled into 61,889 genes, including 39,831 contigs and 22,058 unigenes. In total, we identified 68 novel putative odorant reception genes, including 21 transcripts encoding for putative odorant binding proteins (OBP), six chemosensory proteins (CSP), four sensory neuron membrane proteins (SNMP), 22 odorant receptors (OR), four gustatory receptors (GR), three ionotropic receptors (IR), and eight ionotropic glutamate receptors. We also identified 155 odorant/xenobiotic degradation enzymes from the antennal transcriptome, putatively identified to be involved in olfaction processes including cytochrome P450s, glutathione-S-transferases, and aldehyde dehydrogenase. Predicted protein sequences were compared with counterparts in Tribolium castaneum, Megacyllene caryae, Ips typographus, Dendroctonus ponderosae, and Agrilus planipennis.

CONCLUSION

The antennal transcriptome described here represents the first study of the repertoire of odor processing genes in D. valens. The genes reported here provide a significant addition to the pool of identified olfactory genes in Coleoptera, which might represent novel targets for insect management. The results from our study also will assist with evolutionary analyses of coleopteran olfaction.

Identification of candidate odorant receptors in Asian corn borer Ostrinia furnacalis

In lepidopteran insects, odorant receptors are involved in the perception of sex pheromones and general odorants. In the Asian corn borer, Ostrinia furnacalis, although several pheromone receptors have been identified, no general odorant receptor has been reported. In this study, an RNA sequencing analysis was carried out to identify the whole repertoire of the odorant receptors expressed in the antennae of O. furnacalis. Among 12 million reads obtained from the antennae of male and female moths, 52 candidate odorant receptors were identified, including 45 novel ones. Expression levels of candidate odorant receptors were estimated by read mapping and quantitative reverse transcription PCR. These analyses confirmed that the expression of the previously identified pheromone receptors was highly male biased. In contrast, none of the newly identified odorant receptors showed male-biased expression. Three of the newly identified odorant receptors showed female-biased expression. Two of them were the most highly expressed odorant receptors in the female antennae, suggesting that they may be involved in the detection of odorants important for the induction of female-specific behaviors such as oviposition site selection. In addition, candidate genes of 21 ionotropic receptors, 5 gustatory receptors, 2 sensory neuron membrane proteins, and 26 odorant degrading enzymes were identified. Our results provide a basis for further analysis of the chemosensory system in the Ostrinia species.

Different roles suggested by sex-biased expression and pheromone binding affinity among three pheromone binding proteins in the pink rice borer, Sesamia inferens (Walker) (Lepidoptera: Noctuidae)

Pheromone binding proteins (PBPs) are thought to bind and transport hydrophobic sex pheromone molecules across the aqueous sensillar lymph to specific pheromone receptors on the dendritic membrane of olfactory neurons. A maximum of 3 PBP genes have been consistently identified in noctuid species, and each of them shares high identity with its counterparts in other species within the family. The functionality differences of the 3 proteins are poorly understood. In the present study, 3 PBP cDNAs (SinfPBP1, 2, 3) were identified from the pink rice borer, Sesamia inferens, for the first time. The quantitative real-time PCR indicated that the 3 PBPs displayed similar temporal but very different sex related expression profiles. Expression of SinfPBP1 and SinfPBP2 were highly and moderately male biased, respectively, while SinfPBP3 was slightly female biased, as SinfPBPs were expressed at very different levels (PBP1>PBP2≫PBP3) in male antennae, but at similar levels in female antennae. Furthermore, the 3 SinfPBPs displayed different ligand binding profiles in fluorescence competitive binding assays. SinfPBP1 exhibited high and similar binding affinities to all 3 sex pheromone components (Ki=0.72-1.60 μM), while SinfPBP2 showed selective binding to the alcohol and aldehyde components (Ki=0.78-1.71 μM), and SinfPBP3 showed no obvious binding to the 3 sex pheromone components. The results suggest that SinfPBP1 plays a major role in the reception of female sex pheromones in S. inferens, while SinfPBP3 plays a least role (if any) and SinfPBP2 functions as a recognizer of alcohol and aldehyde components.

Expression of SNMP1 and SNMP2 genes in antennal sensilla of Spodoptera exigua (Hübner)

Sensory neuron membrane proteins (SNMPs) are olfactory-specific, two-transmembrane proteins. Previous publications reported that SNMP1 is expressed on the dendrite membrane of pheromone-sensitive neurons in Heliothis virescens and is an essential cofactor for pheromone detection in Drosophila. In this study, we cloned two SNMP genes (GenBank accession nos. JX469106 and JX469107) from the antenna of the beet armyworm moth Spodoptera exigua (Lepidoptera: Hübner). These SNMP genes are classified into two highly conserved subclades, indicating their importance in physiological activity of lepidopteran insects. SexiSNMP1 is antenna-specific in male and female adults, while SexiSNMP2 is antenna-abundant but also expressed in other chemosensory tissues, particularly proboscises and maxillary palps of adults both sexes. In situ hybridization revealed that both SNMPs are broadly expressed in long and short trichoid and basiconic sensilla. We infer that SNMP1 and SNMP2 act in the detection of the sex pheromone and general odorants.

Functional differentiation of pheromone-binding proteins in the common cutworm Spodoptera litura

Pheromone-binding proteins (PBPs), a sub-family of odorant-binding proteins, are thought primarily to bind and transport the sex pheromones in moths. Considering multiple components of sex pheromone and multiple PBP genes exist in a single species, PBPs may contribute to the discrimination of different sex pheromone components. However, so far this discrimination is still unclear. Our previous ligand-binding assays showed that Spodoptera litura PBP1 (SlitPBP1) did not exhibit an obvious binding specificity among different sex pheromone components. In this study, binding specificity of the other two PBPs in S. litura (SlitPBP2 and SlitPBP3) was further investigated. As a result, SlitPBP2 was capable of binding all four sex pheromone components with similar affinities; whereas SlitPBP3 showed very weak binding affinities to them except Z9,E12-14:Ac. Similar results were also obtained from studied pheromone analogs, to which SlitPBP2 showed much stronger affinities than SlitPBP3. However, both SlitPBP2 and SlitPBP3 exhibited overall weaker affinities to sex pheromones and their analogs than SlitPBP1. In addition, quantitative real time PCR showed that three SlitPBP genes exhibited a very different sex-biased expression in adult antenna with male-biased for SlitPBP1 and SlitPBP2 while female-biased for SlitPBP3. Finally, ligand-binding assays indicated that the two SlitPBPs showed a similar pH-dependent conformational change as reported SlitPBP1, but these three SlitPBPs showed different behavior across a pH range or something similar. Taken together, our data suggest that in S. litura PBP1 and PBP2 may play critical roles in the perception of female sex pheromones, but do not show an obvious discriminative ability among different sex pheromone components; whereas PBP3 may have other functions.

Sex pheromone recognition and immunolocalization of three pheromone binding proteins in the black cutworm moth Agrotis ipsilon

Insect pheromone binding proteins (PBPs) are believed to solubilize and transport hydrophobic sex pheromones across sensillum lymph to membrane-associated pheromone receptors. To address the molecular mechanisms of PBPs in insect pheromone perception, we undertook a systemic study on the PBPs of the black cutworm Agrotis ipsilon at transcript as well as protein level from tissue distribution and cellular localization to pheromone binding affinity. We cloned three full-length PBP genes AipsPBP1-3 from A. ipsilon antennae, and demonstrated that AipsPBP1-3 transcripts were highly expressed in male antennae. The electron microscopic examinations revealed at least six types of olfactory sensilla on male and female antenna: trichodea, chaetica, basiconica, coeloconica, squamiformia and Böhm bristles. The immunocytochemistry results demonstrated that AipsPBP1-3 proteins were strongly expressed in the sensillum lymph of the trichoid sensilla of male moth. The binding assays showed that AipsPBP1 had high binding affinities with the major sex pheromone components Z7-12:Ac and Z9-14:Ac among five related chemicals and was clustered together with the long trichoid sensilla-expressing LdisPBPs of Lymantria dispar. AipsPBP2 showed high binding affinities also with Z11-16:Ac. AipsPBP3 displayed a high affinity only with Z11-16:Ac. Our studies provide further detail evidences for the involvement of moth PBPs in pheromone discrimination and selective recognition of specific components of the female sex pheromone blends.

Single mutation to a sex pheromone receptor provides adaptive specificity between closely related moth species

Sex pheromone communication, acting as a prezygotic barrier to mating, is believed to have contributed to the speciation of moths and butterflies in the order Lepidoptera. Five decades after the discovery of the first moth sex pheromone, little is known about the molecular mechanisms that underlie the evolution of pheromone communication between closely related species. Although Asian and European corn borers (ACB and ECB) can be interbred in the laboratory, they are behaviorally isolated from mating naturally by their responses to subtly different sex pheromone isomers, (E)-12- and (Z)-12-tetradecenyl acetate and (E)-11- and (Z)-11-tetradecenyl acetate (ACB: E12, Z12; ECB; E11, Z11). Male moth olfactory systems respond specifically to the pheromone blend produced by their conspecific females. In vitro, ECB(Z) odorant receptor 3 (OR3), a sex pheromone receptor expressed in male antennae, responds strongly to E11 but also generally to the Z11, E12, and Z12 pheromones. In contrast, we show that ACB OR3, a gene that has been subjected to positive selection (ω = 2.9), responds preferentially to the ACB E12 and Z12 pheromones. In Ostrinia species the amino acid residue corresponding to position 148 in transmembrane domain 3 of OR3 is alanine (A), except for ACB OR3 that has a threonine (T) in this position. Mutation of this residue from A to T alters the pheromone recognition pattern by selectively reducing the E11 response ∼14-fold. These results suggest that discrete mutations that narrow the specificity of more broadly responsive sex pheromone receptors may provide a mechanism that contributes to speciation.

Molecular characterization, expression patterns, and ligand-binding properties of two odorant-binding protein genes from Orthaga achatina (Butler) (Lepidoptera: Pyralidae)

It is postulated that insect pheromone-binding proteins (PBPs) are involved in sex pheromone reception, while the general odorant-binding proteins (GOBPs) are involved in reception of the general odorants including plant volatiles. However, this functional specificity is not completely conclusive. In the present study, full-length sequences of two new OBP genes were molecularly identified as OachPBP1 and OachGOBP2 from Orthaga achatina, an important pest of the camphor tree Cinnamomum camphora. Quantification of transcript levels by qRT-PCR showed that the two genes highly expressed in antennae, with OachPBP1 male-biased and OachGOBP2 similar between sexes. These expression patterns are consistent with the generally proposed functions of PBPs and GOBPs. With the recombinant proteins obtained by a bacterial expression system, the binding specificity of these proteins was further investigated and compared using the competitive binding assay. OachPBP1 exhibited high binding affinities with all three putative sex pheromones and 10 pheromone analogs, supporting its role in pheromone reception. On the other hand, in addition to binding with some plant volatiles, OachGOBP2 surprisingly displayed similar or even higher binding affinities with the sex pheromones than OachPBP1. Therefore, we propose that OachGOBP2 might play roles in reception of sex pheromone. Additionally, plant volatiles farnesol and farnesene showed high binding with both OachGOBP2 and OachPBP1, suggesting that these volatile chemicals have regulatory functions in the behavior of O. achatina.

Binding properties of pheromone-binding protein 1 from the common cutworm Spodoptera litura

Pheromone-binding proteins (PBPs) were formerly thought to act as passive pheromone carriers. However, recent studies, particularly in Drosophila melanogaster, suggest that PBPs are involved in the recognition of semiochemicals, thus making ligand-binding studies more meaningful. Previously, we cloned three PBPs from Spodoptera litura (Slit), and showed that SlitPBP1 is much more abundant than the other two, particularly in male antennae. To investigate the ligand specificity of SlitPBP1, we expressed the protein in a bacterial system and performed binding experiments with the three components of the specific sex pheromones (Z9-14:Ac, Z9,E11-14:Ac and Z9,E12-14:Ac), as well as with 26 volatile ligands. The results indicated that SlitPBP1 bound all three sex pheromone components with dissociation constants between 0.6 and 1.1 μM. The same protein also bound with comparable affinities several pheromone analogs, but not plant volatiles. The presence of a double bond was the most important element for a strong binding, while its position and configuration also affected the affinity. Finally, the binding of pheromone components is strongly affected by pH, showing a critical pH value corresponding to isoelectric point of the protein. This suggests that a pH-dependent conformational mechanism might exist in SlitPBP1 for pheromone binding and release.

Characterization of olfactory genes in the antennae of the Southern house mosquito, Culex quinquefasciatus

Odorant reception in insects is mediated by different families of olfactory proteins. Here we focus on the characterization of odorant-binding proteins (OBPs), "plus-C" odorant-binding proteins ("plus-C" OBPs), chemosensory proteins (CSPs) and sensory neuron membrane proteins (SNMPs) families from the Southern house mosquito, Culex quinquefasciatus, a vector of pathogens implicated in multiple human diseases. Using bioinformatics and molecular approaches, we have identified a diversity of genes in the genome of Culex quinquefasciatus and examined their expression profiles by RT-PCR and real-time quantitative PCR. Based on their high transcript enrichment in female antennae compared to non-olfactory tissues, we have identified twelve OBPs, two "plus-C" OBPs and two SNMPs that likely play important roles in odorant reception. Transcripts of two genes were clearly enriched in female antennae compared to male antennae, whereas other genes displayed relatively equivalent transcript levels in antennae of both sexes. Additionally, eight genes were found to be transcribed at very high levels in female antennae compared to CquiOR7, suggesting they might encode highly abundant olfactory proteins. Comparative analysis across different mosquito species revealed that olfactory genes of Culex quinquefasciatus are related to putative orthologs in other species, indicating that they might perform similar functions. Understanding how mosquitoes are able to detect ecologically relevant odorant cues might help designing better control strategies. We have identified olfactory genes from different families which are likely important in Culex quinquefasciatus behaviors, thus paving the way towards a better understanding of the diversity of proteins involved in the reception of semiochemicals in this species.