Characterization and cDNA cloning of the pheromone-binding protein from the tobacco hornworm, Manduca sexta: a tissue-specific developmentally regulated protein

Expression and functional characterization of odorant-binding protein 2 in the predatory mite Neoseiulus barkeri

Olfaction plays a crucial role for arthropods in foraging, mating, and oviposition. The odorant-binding protein (OBP) gene is considered one of the most important olfactory genes. However, little is known about its functions in predatory mites. Here, we used Neoseiulus barkeri, an important commercialized natural pest control, to explore the chemosensory characteristics of OBP. In this study, N. barkeri was attracted by methyl salicylate (MeSA) and showed higher crawling speeds under MeSA treatment. Then, we identified and cloned an OBP gene named Nbarobp2 and analyzed its expression profiles in the predatory mite. Nbarobp2 was 663 bp, was highly expressed in larval and nymphal stages, and was significantly upregulated in N. barkeri under MeSA treatment. Nbarobp2 encoded 202 amino acid residues with a molecular weight of 23 kDa (after removing the signal peptide). Sequence comparisons revealed that the OBPs in Arachnida shared 6 conserved cysteine sites, but were distinguishable from the OBPs of Insecta on the phylogenetic tree. RNA interference, Western blotting, and binding affinity assays further proved that Nbarobp2 was involved in volatile perception in predatory mites. This study shed light on the functional characteristics of OBPs in predatory mites, providing a new insight for better biological control.

Molecular Characterization and Expression Patterns of Two Pheromone-Binding Proteins from the Diurnal Moth Phauda flammans (Walker) (Lepidoptera: Zygaenoidea: Phaudidae)

Sex pheromone-binding proteins (PBPs) play an important role in sex pheromone recognition in Lepidoptera. However, the mechanisms of chemical communication mediating the response to sex pheromones remain unclear in the diurnal moths of the superfamily Zygaenoidea. In this study, Phauda flammans (Walker) (Lepidoptera: Zygaenoidea: Phaudidae) was used as a model insect to explore the molecular mechanism of sex pheromone perception in the superfamily Zygaenoidea. Two novel pheromone-binding proteins (PflaPBP1 and PflaPBP2) from P. flammans were identified. The two pheromone-binding proteins were predominantly expressed in the antennae of P. flammans male and female moths, in which PflaPBP1 had stronger binding affinity to the female sex pheromones Z-9-hexadecenal and (Z, Z, Z)-9, 12, 15-octadecatrienal, PflaPBP2 had stronger binding affinity only for (Z, Z, Z)-9, 12, 15-octadecatrienal, and no apparent binding affinity to Z-9-hexadecenal. The molecular docking results indicated that Ile 170 and Leu 169 are predicted to be important in the binding of the sex pheromone to PflaPBP1 and PflaPBP2. We concluded that PflaPBP1 and PflaPBP2 may be responsible for the recognition of two sex pheromone components and may function differently in female and male P. flammans. These results provide a foundation for the development of pest control by exploring sex pheromone blocking agents and the application of sex pheromones and their analogs for insect pests in the superfamily Zygaenoidea.

The Adelphocoris lineolatus OBP4: Support for evolutionary and functional divergence of a mirid pheromone-binding protein from that found in lepidopteran moths

Pheromone-binding proteins (PBPs) have been extensively investigated in lepidopteran moths, but their evolution and function in hemipteran species remain unclear. Our previous study demonstrated that an odorant-binding protein, OBP4, of the mirid bug Adelphocoris lineolatus functions as a candidate hemipteran PBP but clustered with lepidopteran antennae-binding proteins (ABPs) rather than in the PBP/general odorant-binding protein (GOBP) clade. In this study, we hypothesized that origin and function of PBPs in hemipteran bugs may differ from those of lepidopteran moths. To test this hypothesis, we first constructed a phylogenetic tree using insect OBPs from sister hemipteran and holometabolous lineages, and the results indicated that neither OBP4 nor other types of candidate PBPs of mirid bugs clustered with the lepidopteran PBP/GOBP clade. Then, a fluorescence competitive binding assay was employed to determine binding affinities of recombinant OBP4 protein to host plant volatiles, with functional groups different from A. lineolatus sex pheromone components. The results revealed that OBP4 highly bound the female adult attractant 3-hexanone and 15 other mirid bug biologically active plant volatiles. Finally, we examined cellular expression profiles of OBP4 in putative antennal sensilla that are related to female A. lineolatus host plant location. The fluorescence in situ hybridization and immunocytochemical labeling assay showed that the OBP4 gene was highly expressed in the multiporous olfactory sensilla medium-long sensilla basiconica rather than in the short sensilla basiconica or uniporous sensilla chaetica. These results, together with those of our previous studies, indicate that OBP4 not only functions in recognition of bug-produced sex pheromones in males, but is probably involved in detection of host plant volatiles in both A. lineolatus sexes. Our findings support the hypothesis that the origin and function of PBPs in hemipteran bugs differ from those of well-known PBPs in lepidopteran moths, which provides a novel perspective on evolutionary mechanisms of sex pheromone communication across insect orders.

The 40-Year Mystery of Insect Odorant-Binding Proteins

The survival of insects depends on their ability to detect molecules present in their environment. Odorant-binding proteins (OBPs) form a family of proteins involved in chemoreception. While OBPs were initially found in olfactory appendages, recently these proteins were discovered in other chemosensory and non-chemosensory organs. OBPs can bind, solubilize and transport hydrophobic stimuli to chemoreceptors across the aqueous sensilla lymph. In addition to this broadly accepted "transporter role", OBPs can also buffer sudden changes in odorant levels and are involved in hygro-reception. The physiological roles of OBPs expressed in other body tissues, such as mouthparts, pheromone glands, reproductive organs, digestive tract and venom glands, remain to be investigated. This review provides an updated panorama on the varied structural aspects, binding properties, tissue expression and functional roles of insect OBPs.

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.

Organophosphorus insecticide interacts with the pheromone-binding proteins of Athetis lepigone: Implication for olfactory dysfunction

Athetis lepigone is one of the most severe polyphagous pests, and it has developed resistance to different chemical insecticides. Insects primarily rely on the olfactory system to recognize various environmental chemicals, including xenobiotics such as insecticides. Here, we expressed two A. lepigone pheromone-binding proteins (AlepPBP2 and AlepPBP3), and observed they had higher binding affinities to phoxim than other insecticides, with Ki was 3.30 ± 0.38 μM and 3.27 ± 0.10 μM, respectively. Molecular dynamics simulation, binding mode analysis, and computational alanine scanning showed that six residues (Phe15, Phe39, Ile55, Leu65, Ile97, and Phe122) of AlepPBP2 and three residues (Phe12, Ile52, and Ile134) of AlepPBP3 maybe as potential residues that can change protein ability to bind an organophosphorus insecticide phoxim. Then, we used site-directed mutagenesis assay to mutate these residues into alanine, respectively. Subsequently, the binding assays displayed that Phe15, Phe39, and Ile97 of AlepPBP2, Phe12 and Ile134 of AlepPBP3 caused a significant decrease of AlepPBPs binding ability to phoxim, suggesting they should play crucial roles in the AlepPBPs/phoxim interactions. Our findings could further advance in using PBPs as unique targets to design and develop precise and environmentally-friendly pest control agents with high insecticidal potential using a computer-aided drug design (CADD) approach.

The sensilla trichodea-biased EoblPBP1 binds sex pheromones and green leaf volatiles in Ectropis obliqua Prout, a geometrid moth pest that uses Type-II sex pheromones

Pheromone-binding proteins (PBPs) are considered to play critical roles in sex pheromone detection. Lepidopteran moths can be divided into two taxa, those that use Type-I sex pheromones, such as C10-C18 unsaturated aldehydes, alcohols and acetates, and those that use Type-II pheromones, which are C17-C23 polyunsaturated hydrocarbons and their epoxide derivatives. To date, nearly all the characterized PBPs have been reported in moths with Type-I sex pheromones, and the physiological functions of PBPs in moths that use Type-II sex pheromones remains unclear. In the present study we functionally examine EoblPBP1 in Ectropis obliqua Prout, an important geometrid moth pest that uses Type-II sex pheromones. The phylogenetic analysis of the sequence indicated that EoblPBP1 clustered together with ScerPBP1, a geometrid PBP for detecting Type-II sex pheromones. Scanning electron microscopy showed that E. obliqua moths of both sexes mainly had six types of antennal sensilla, including two types of sensilla trichodea, Str-I and Str-II, sensilla basiconica (Sba), sensilla styloconica (Sst), sensilla chaetica (Sch) and sensilla auricillica (Sau). Of these, Str-I was confirmed to be male moth-specific and had five different subtypes. Fluorescence in situ hybridization revealed that EoblPBP1 was primarily expressed at the base of Str-I. A comparative binding assay showed that recombinant EoblPBP1 bound three sex pheromone components of E. obliqua, demonstrating its involvement in the detection of Type-II sex pheromones. Besides, EoblPBP1 also highly bound unsaturated acetates pheromones and the green leaf volatiles. These results indicate that PBP1 is associated with detecting Type-II sex pheromones in E. obliqua but cannot differentiate Type-II sex pheromones from Type-I sex pheromones or green leaf volatiles. Our findings provide a foundation for further study on molecular basis of Type-II sex pheromone recognition in lepidopteran moths.

Pheromone Binding Protein EhipPBP1 Is Highly Enriched in the Male Antennae of the Seabuckthorn Carpenterworm and Is Binding to Sex Pheromone Components

The seabuckthorn carpenterworm moth Eogystia hippophaecolus is a major threat to seabuckthorn plantations, causing considerable ecological and economic losses in China. Transcriptomic analysis of E. hippophaecolus previously identified 137 olfactory proteins, including three pheromone-binding proteins (PBPs). We investigated the function of E. hippophaecolus PBP1 by studying its mRNA and protein expression profiles and its binding ability with different compounds. The highest levels of expression were in the antennae, particularly in males, with much lower levels of expression in the legs and external genitals. Recombinant PBP1 showed strong binding to sex-pheromone components, suggesting that antennal EhipPBP1 is involved in binding sex-pheromone components during pheromone communication.

Under-Expression of Chemosensory Genes in Domiciliary Bugs of the Chagas Disease Vector Triatoma brasiliensis

BACKGROUND

In Latin America, the bloodsucking bugs Triatominae are vectors of Trypanosoma cruzi, the parasite that causes Chagas disease. Chemical elimination programs have been launched to control Chagas disease vectors. However, the disease persists because native vectors from sylvatic habitats are able to (re)colonize houses-a process called domiciliation. Triatoma brasiliensis is one example. Because the chemosensory system allows insects to interact with their environment and plays a key role in insect adaption, we conducted a descriptive and comparative study of the chemosensory transcriptome of T. brasiliensis samples from different ecotopes.

METHODOLOGY/PRINCIPAL FINDING

In a reference transcriptome built using de novo assembly, we found transcripts encoding 27 odorant-binding proteins (OBPs), 17 chemosensory proteins (CSPs), 3 odorant receptors (ORs), 5 transient receptor potential channel (TRPs), 1 sensory neuron membrane protein (SNMPs), 25 takeout proteins, 72 cytochrome P450s, 5 gluthatione S-transferases, and 49 cuticular proteins. Using protein phylogenies, we showed that most of the OBPs and CSPs for T. brasiliensis had well supported orthologs in the kissing bug Rhodnius prolixus. We also showed a higher number of these genes within the bloodsucking bugs and more generally within all Hemipterans compared to the other species in the super-order Paraneoptera. Using both DESeq2 and EdgeR software, we performed differential expression analyses between samples of T. brasiliensis, taking into account their environment (sylvatic, peridomiciliary and domiciliary) and sex. We also searched clusters of co-expressed contigs using HTSCluster. Among differentially expressed (DE) contigs, most were under-expressed in the chemosensory organs of the domiciliary bugs compared to the other samples and in females compared to males. We clearly identified DE genes that play a role in the chemosensory system.

CONCLUSION/SIGNIFICANCE

Chemosensory genes could be good candidates for genes that contribute to adaptation or plastic rearrangement to an anthropogenic system. The domiciliary environment probably includes less diversity of xenobiotics and probably has more stable abiotic parameters than do sylvatic and peridomiciliary environments. This could explain why both detoxification and cuticle protein genes are less expressed in domiciliary bugs. Understanding the molecular basis for how vectors adapt to human dwellings may reveal new tools to control disease vectors; for example, by disrupting chemical communication.

Multifaceted biological insights from a draft genome sequence of the tobacco hornworm moth, Manduca sexta

Manduca sexta, known as the tobacco hornworm or Carolina sphinx moth, is a lepidopteran insect that is used extensively as a model system for research in insect biochemistry, physiology, neurobiology, development, and immunity. One important benefit of this species as an experimental model is its extremely large size, reaching more than 10 g in the larval stage. M. sexta larvae feed on solanaceous plants and thus must tolerate a substantial challenge from plant allelochemicals, including nicotine. We report the sequence and annotation of the M. sexta genome, and a survey of gene expression in various tissues and developmental stages. The Msex_1.0 genome assembly resulted in a total genome size of 419.4 Mbp. Repetitive sequences accounted for 25.8% of the assembled genome. The official gene set is comprised of 15,451 protein-coding genes, of which 2498 were manually curated. Extensive RNA-seq data from many tissues and developmental stages were used to improve gene models and for insights into gene expression patterns. Genome wide synteny analysis indicated a high level of macrosynteny in the Lepidoptera. Annotation and analyses were carried out for gene families involved in a wide spectrum of biological processes, including apoptosis, vacuole sorting, growth and development, structures of exoskeleton, egg shells, and muscle, vision, chemosensation, ion channels, signal transduction, neuropeptide signaling, neurotransmitter synthesis and transport, nicotine tolerance, lipid metabolism, and immunity. This genome sequence, annotation, and analysis provide an important new resource from a well-studied model insect species and will facilitate further biochemical and mechanistic experimental studies of many biological systems in insects.

Discrimination of cis-trans sex pheromone components in two sympatric Lepidopteran species

Pheromone-binding proteins (PBPs) play an important role in the recognition of pheromones by insects. However, the abilities of these PBPs to discriminate pheromone components and recognize the isomers are unclear. Dendrolimus houi and Dendrolimus kikuchii are two sympatric coniferous pests whose pheromones have cis-trans isomers. We used these insect species to detect the precise recognition abilities of PBPs. The four PBPs examined showed male-biased antenna-intensive expression patterns, whereas PBP1 showed higher expression than PBP2 in the antenna. DhouPBP1 only bound to a minor interspecific pheromone component, whereas DhouPBP2 bound to all three intraspecific components and another minor interspecific component. DkikPBP1 and DkikPBP2 could recognize all three intraspecific components with affinities negatively correlated with their ratios, and they bound to interspecific pheromones with affinity that was positively correlated with the ratios. The four PBPs have different cis-trans isomer discrimination abilities, i.e., DhouPBP1 and DkikPBP1 could not discriminate the two cis-trans isomer pairs of pheromones from the two species, whereas DhouPBP2 could discriminate between both pairs, and DkikPBP2 could only discriminate one pair. Overall, PBPs from D. houi and D. kikuchii use different strategies to help the moths to discriminate the intra- and interspecific pheromone components. Our work will contribute to better understanding of the sex pheromone recognition mechanism in these two sister species of moths and provide insights into more effective management practices of these pest species.

Pheromone Autodetection: Evidence and Implications

Olfactory communication research with insects utilizing sex pheromones has focused on the effects of pheromones on signal receivers. Early pheromone detection studies using the silkworm moth, Bombyx mori L., and Saturniids led to the assumption that emitters, especially females, are unable to detect their own pheromone. Pheromone anosmia, i.e., the inability of females to detect their conspecific sex pheromone, was often assumed, and initially little attention was paid to female behaviors that may result from autodetection, i.e., the ability of females to detect their sex pheromone. Detection of conspecific pheromone plumes from nearby females may provide information to improve chances of mating success and progeny survival. Since the first documented example in 1972, numerous occurrences of autodetection have been observed and verified in field and laboratory studies. We summarize here a significant portion of research relating to autodetection. Electrophysiological and behavioral investigations, as well as expression patterns of proteins involved in pheromone autodetection are included. We discuss problems inherent in defining a boundary between sex and aggregation pheromones considering the occurrence of autodetection, and summarize hypothesized selection pressures favoring autodetection. Importance of including autodetection studies in future work is emphasized by complications arising from a lack of knowledge combined with expanding the use of pheromones in agriculture.

The Lepidoptera Odorant Binding Protein gene family: Gene gain and loss within the GOBP/PBP complex of moths and butterflies

Butterflies and moths differ significantly in their daily activities: butterflies are diurnal while moths are largely nocturnal or crepuscular. This life history difference is presumably reflected in their sensory biology, and especially the balance between the use of chemical versus visual signals. Odorant Binding Proteins (OBP) are a class of insect proteins, at least some of which are thought to orchestrate the transfer of odor molecules within an olfactory sensillum (olfactory organ), between the air and odor receptor proteins (ORs) on the olfactory neurons. A Lepidoptera specific subclass of OBPs are the GOBPs and PBPs; these were the first OBPs studied and have well documented associations with olfactory sensilla. We have used the available genomes of two moths, Manduca sexta and Bombyx mori, and two butterflies, Danaus plexippus and Heliconius melpomene, to characterize the GOBP/PBP genes, attempting to identify gene orthologs and document specific gene gain and loss. First, we identified the full repertoire of OBPs in the M. sexta genome, and compared these with the full repertoire of OBPs from the other three lepidopteran genomes, the OBPs of Drosophila melanogaster and select OBPs from other Lepidoptera. We also evaluated the tissue specific expression of the M. sexta OBPs using an available RNAseq databases. In the four lepidopteran species, GOBP2 and all PBPs reside in single gene clusters; in two species GOBP1 is documented to be nearby, about 100 kb from the cluster; all GOBP/PBP genes share a common gene structure indicating a common origin. As such, the GOBP/PBP genes form a gene complex. Our findings suggest that (1) the lepidopteran GOBP/PBP complex is a monophyletic lineage with origins deep within Lepidoptera phylogeny, (2) within this lineage PBP gene evolution is much more dynamic than GOBP gene evolution, and (3) butterflies may have lost a PBP gene that plays an important role in moth pheromone detection, correlating with a shift from olfactory (moth) to visual (butterfly) communication, at least regarding long distance mate recognition. These findings will be clarified by additional lepidopteran genomic data, but the observation that moths and butterflies share most of the PBP/GOBP genes suggests that they also share common chemosensory-based behavioral pathways.

Two subclasses of odorant-binding proteins in Spodoptera exigua display structural conservation and functional divergence

Although many studies on lepidopteran pheromone-binding proteins (PBPs)/ general odorant-binding proteins (GOBPs) have been reported, the functional differentiation within and between the two odorant-binding protein (OBP) subclasses is still elusive. Here we conducted a comparative study on three SexiPBPs and two SexiGOBPs in Spodoptera exigua. Results showed that all five SexiPBP/GOBP genes have the same intron numbers and conserved exon/intron splice sites. Reverse transcription PCR results showed that these five SexiPBP/GOBPs were primarily expressed in antennae of both sexes and some were also detected in other tissues. Further, quantitative real-time PCR showed that five SexiPBP/GOBPs had different sex-biased expression patterns, with PBP1 being highly male-biased (5.96-fold difference) and PBP3 slightly female-biased (2.43-fold difference), while PBP2 and two GOBPs were approximately sex-equivalent (the absolute value<1.90-fold difference). Binding assays showed that all three SexiPBPs could bind all six sex pheromone components, but SexiPBP1 had much higher affinities [dissociation constant (Ki ) <1.10 μM] than did the other two SexiPBPs (Ki  >1.20 μM). Very intriguingly, SexiGOBP2 displayed even stronger binding to five sex pheromone components (Ki  <0.40 μM) than SexiPBP1. In contrast, SexiGOBP1 only exhibited weak binding to three alcohol-pheromone components. Similar results were obtained for tested pheromone analogues. In addition, each of SexiPBP/GOBPs selectively bound some plant odorants with considerable affinities (Ki  <10.0 μM). Taken together, of the three SexiPBPs, SexiPBP1 may play the most important role in female sex pheromone reception, and additionally all three SexiPBPs can detect some plant odorants, while SexiGOBP2 may be involved in the detection of female sex pheromones in addition to plant odorants. The results strongly suggest functional differentiation within and between the two OBP sub-classes.

Antennal uridine diphosphate (UDP)-glycosyltransferases in a pest insect: diversity and putative function in odorant and xenobiotics clearance

Uridine diphosphate UDP-glycosyltransferases (UGTs) are detoxification enzymes widely distributed within living organisms. They are involved in the biotransformation of various lipophilic endogenous compounds and xenobiotics, including odorants. Several UGTs have been reported in the olfactory organs of mammals and involved in olfactory processing and detoxification within the olfactory mucosa but, in insects, this enzyme family is still poorly studied. Despite recent transcriptomic analyses, the diversity of antennal UGTs in insects has not been investigated. To date, only three UGT cDNAs have been shown to be expressed in insect olfactory organs. In the present study, we report the identification of eleven putative UGTs expressed in the antennae of the model pest insect Spodoptera littoralis. Phylogenetic analysis revealed that these UGTs belong to five different families, highlighting their structural diversity. In addition, two genes, UGT40R3 and UGT46A6, were either specifically expressed or overexpressed in the antennae, suggesting specific roles in this sensory organ. Exposure of male moths to the sex pheromone and to a plant odorant differentially downregulated the transcription levels of these two genes, revealing for the first time the regulation of insect UGTs by odorant exposure. Moreover, the specific antennal gene UGT46A6 was upregulated by insecticide topical application on antennae, suggesting its role in the protection of the olfactory organ towards xenobiotics. This work highlights the structural and functional diversity of UGTs within this highly specialized tissue.

Molecular characterization, expression pattern, and ligand-binding property of three odorant binding protein genes from Dendrolimus tabulaeformis

Odorant binding proteins (OBPs) play important roles in insect olfactory processes. The Chinese pine caterpillar moth, Dendrolimus tabulaeformis (Lepidoptera, Lasiocampidae) is a serious economic pest in China, and the pheromones of this species have been identified to monitor their presence. However, the molecular mechanisms by which D. tabulaeformis perceive pheromones and host volatiles remain unknown. In this study, we identified and characterized three new OBPs, including one pheromone binding protein (PBP1) and two general odor binding proteins (GOBPs), from antennal cDNA of D. tabulaeformis. The deduced amino acid sequences of DtabPBP1, DtabGOBP1, and DtabGOBP2 revealed mature proteins of 140, 147, and 140 amino acids, respectively. Each has six cysteine residues in conserved positions relative to other known OBPs. Amino-acid alignments indicated that the two GOBPs are more conserved (DtabGOBP1 is 52.9–67.4 % identical to orthologs from other Lepidoptera, and DtabGOBP2 is 55.2–81.8 % identical) than the PBP (32.5–46.0 %). Real-time PCR indicated tissue- and sex-specific expression patterns of the three genes. DtabPBP1 was mainly expressed in the antennae of males, whereas female antennae had only 1.09 % the expression in male antennae. Both DtabGOBP1 and DtabGOBP2 were more highly expressed in antennae than in other tissues, while DtabGOBP1 was more abundant in male antennae and DtabGOBP2 in female antennae. In addition, the binding specificities of the three proteins were investigated, and all three OBPs exhibited high binding affinities for the pheromone component (5Z,7E)-5,7-dodecadien-1-yl propionate (Z5,E7-12:OPr). This suggests a role in binding pheromone for GOBPs, as well as PBP1, in D. tabulaeformis.

Cytochrome P450s and cytochrome P450 reductase in the olfactory organ of the cotton leafworm Spodoptera littoralis

Cytochrome P450 enzymes (P450s) are involved in many physiological functions in insects, such as the metabolism of signal molecules, adaptation to host plants and insecticide resistance. Several P450s have been reported in the olfactory organs of insects, the antennae, and have been proposed to play a role in odorant processing and/or xenobiotic metabolism. Despite recent transcriptomic analyses in several species, the diversity of antennal P450s in insects has not yet been investigated. Here, we report the identification of 37 putative P450s expressed in the antennae of the pest moth Spodoptera littoralis, as well as the characterization of a redox partner, cytochrome P450 reductase (CPR). Phylogenetic analysis revealed that S. littoralis P450s belong to four clades defined by their conservation with vertebrate P450s and their cellular localization. Interestingly, the CYP3 and CYP4 clans, which have been described to be mainly involved in the metabolism of plant compounds and xenobiotics, were largely predominant. More surprisingly, two P450s related to ecdysteroid metabolism were also identified. Expression patterns in adult and larval tissues were studied. Eight P450s appeared to be specific to the chemosensory organs, ie the antennae and proboscis, suggesting a specific role in odorant and tastant processing. Moreover, exposure of males to a plant odorant down-regulated the transcript level of CPR, revealing for the first time the regulation of this gene by odorants within insect antennae. This work suggests that the antennae of insects are a key site for P450-mediated metabolism of a large range of exogenous and endogenous molecules.

Degradation of pheromone and plant volatile components by a same odorant-degrading enzyme in the cotton leafworm, Spodoptera littoralis

Background

Odorant-Degrading Enzymes (ODEs) are supposed to be involved in the signal inactivation step within the olfactory sensilla of insects by quickly removing odorant molecules from the vicinity of the olfactory receptors. Only three ODEs have been both identified at the molecular level and functionally characterized: two were specialized in the degradation of pheromone compounds and the last one was shown to degrade a plant odorant.

Methodology

Previous work has shown that the antennae of the cotton leafworm Spodoptera littoralis, a worldwide pest of agricultural crops, express numerous candidate ODEs. We focused on an esterase overexpressed in males antennae, namely SlCXE7. We studied its expression patterns and tested its catalytic properties towards three odorants, i.e. the two female sex pheromone components and a green leaf volatile emitted by host plants.

Conclusion

SlCXE7 expression was concomitant during development with male responsiveness to odorants and during adult scotophase with the period of male most active sexual behaviour. Furthermore, SlCXE7 transcription could be induced by male exposure to the main pheromone component, suggesting a role of Pheromone-Degrading Enzyme. Interestingly, recombinant SlCXE7 was able to efficiently hydrolyze the pheromone compounds but also the plant volatile, with a higher affinity for the pheromone than for the plant compound. In male antennae, SlCXE7 expression was associated with both long and short sensilla, tuned to sex pheromones or plant odours, respectively. Our results thus suggested that a same ODE could have a dual function depending of it sensillar localisation. Within the pheromone-sensitive sensilla, SlCXE7 may play a role in pheromone signal termination and in reduction of odorant background noise, whereas it could be involved in plant odorant inactivation within the short sensilla.

Antennal transcriptome of Manduca sexta

In recent years, considerable progress has been made in understanding the molecular mechanisms underlying olfaction in insects. Because of the diverse nature of the gene families involved, this process has largely relied on genomic data. As a consequence, studies have focused on a small subset of species with extensive genomic information. For Lepidoptera, a large order historically crucial to olfactory research, this circumstance has mostly limited advances to the domesticated species Bombyx mori, with some progress in the noctuid Heliothis virescens based on a nonpublic partial genome database. Because of the limited behavioral repertoire and nonexistent ecological importance of Bombyx, molecular data on the tobacco hornworm Manduca sexta are of utmost importance, especially with regards to its position as a classical olfactory model and its complex natural behavior. Here we present the use of transcriptomic and microarray data to identify members of the main olfactory gene families of Manduca. To assess the quality of our data, we correlate information on expressed receptor genes with detailed morphological data on the antennal lobe. Finally, we compare the expression of the near-complete transcript sets in male and female antennae.

Candidate chemosensory ionotropic receptors in a Lepidoptera

A new family of candidate chemosensory ionotropic receptors (IRs) related to ionotropic glutamate receptors (iGluRs) was recently discovered in Drosophila melanogaster. Through Blast analyses of an expressed sequenced tag library prepared from male antennae of the noctuid moth Spodoptera littoralis, we identified 12 unigenes encoding proteins related to D. melanogaster and Bombyx mori IRs. Their full length sequences were obtained and the analyses of their expression patterns suggest that they were exclusively expressed or clearly enriched in chemosensory organs. The deduced protein sequences were more similar to B. mori and D. melanogaster IRs than to iGluRs and showed considerable variations in the predicted ligand-binding domains; none have the three glutamate-interacting residues found in iGluRs, suggesting different binding specificities. Our data suggest that we identified members of the insect IR chemosensory receptor family in S. littoralis and we report here the first demonstration of IR expression in Lepidoptera.

Characterization of an antennal carboxylesterase from the pest moth Spodoptera littoralis degrading a host plant odorant

BACKGROUND

Carboxyl/cholinesterases (CCEs) are highly diversified in insects. These enzymes have a broad range of proposed functions, in neuro/developmental processes, dietary detoxification, insecticide resistance or hormone/pheromone degradation. As few functional data are available on purified or recombinant CCEs, the physiological role of most of these enzymes is unknown. Concerning their role in olfaction, only two CCEs able to metabolize sex pheromones have been functionally characterized in insects. These enzymes are only expressed in the male antennae, and secreted into the lumen of the pheromone-sensitive sensilla. CCEs able to hydrolyze other odorants than sex pheromones, such as plant volatiles, have not been identified.

METHODOLOGY

In Spodoptera littoralis, a major crop pest, a diversity of antennal CCEs has been previously identified. We have employed here a combination of molecular biology, biochemistry and electrophysiology approaches to functionally characterize an intracellular CCE, SlCXE10, whose predominant expression in the olfactory sensilla suggested a role in olfaction. A recombinant protein was produced using the baculovirus system and we tested its catabolic properties towards a plant volatile and the sex pheromone components.

CONCLUSION

We showed that SlCXE10 could efficiently hydrolyze a green leaf volatile and to a lesser extent the sex pheromone components. The transcript level in male antennae was also strongly induced by exposure to this plant odorant. In antennae, SlCXE10 expression was associated with sensilla responding to the sex pheromones and to plant odours. These results suggest that a CCE-based intracellular metabolism of odorants could occur in insect antennae, in addition to the extracellular metabolism occurring within the sensillar lumen. This is the first functional characterization of an Odorant-Degrading Enzyme active towards a host plant volatile.

Sex-specific odorant receptors of the tobacco hornworm manduca sexta

As odor information plays a vital role in the life of moths, their olfactory sense has evolved into a highly specific and sensitive apparatus relevant to reproduction and survival. The key players in the detection of odorants are olfactory receptor (OR) proteins. Here we identify four OR-encoding genes differentially expressed in the antennae of males and females of the sphingid moth Manduca sexta. Two male-specific receptors (the previously reported MsexOR-1 and the newly identified MsexOR-4) show great resemblance to other male moth pheromone ORs. The putative pheromone receptors are co-expressed with the co-receptor involved in general odorant signal transduction, the DmelOr83b homolog MsexOR-2. One female-specific receptor (MsexOR-5) displays similarities to BmorOR-19, a receptor in Bombyx mori tuned to the detection of the plant odor linalool.

A diversity of putative carboxylesterases are expressed in the antennae of the noctuid moth Spodoptera littoralis

Recent studies have suggested that pheromone-degrading enzymes belonging to the carboxylesterase family could play a role in the dynamics of the olfactory response to acetate sex pheromones in insects. Bioinformatic analyses of a male antennal expressed sequence tag library allowed the identification of 19 putative esterase genes expressed in the antennae of the moth Spodoptera littoralis. Phylogenetic analysis revealed that these genes belong to different insect esterase clades, defined by their putative cellular localization and substrate preferences. Interestingly, two of the 19 genes appeared to be antennal specific, suggesting a specific role in olfactory processing. This high esterase diversity suggested that the antennae are the location for intense esterase-based metabolism, against potentially a large range of exogenous and endogenous molecules.

Odorant-binding proteins in insects

Our understanding of the molecular and biochemical mechanisms that mediate chemoreception in insects has been greatly improved after the discovery of olfactory and taste receptor proteins. However, after 50 years of the discovery of first insect sex pheromone from the silkmoth Bombyx mori, it is still unclear how hydrophobic compounds reach the dendrites of sensory neurons in vivo across aqueous space and interact with the sensory receptors. The presence of soluble polypeptides in high concentration in the lymph of chemosensilla still poses unanswered questions. More than two decades after their discovery and despite the wealth of structural and biochemical information available, the physiological function of odorant-binding proteins (OBPs) is not well understood. Here, I review the structural properties of different subclasses of insect OBPs and their binding to pheromones and other small ligands. Finally, I discuss current ideas and models on the role of such proteins in insect chemoreception.

Expression of differential antennal proteins in males and females of an important crop pest, Sesamia nonagrioides

Pest damage causes important decrease in crop yield every year all over the world, particularly by Lepidoptera. Characterization of the antennal proteins implicated in the reproduction of Lepidoptera will help to develop new methods for pest management and contribute to sustainable agriculture and biodiversity maintenance. We present herein the characterization of some antennal proteins of Sesamia nonagrioides by proteomic techniques such as two-dimensional electrophoresis, MALDI-TOF MS, and electrospray ionization tandem mass spectrometry (ESI-MS/MS). The antennal proteins expressed in both sexes were analyzed and more than 800 spots were detected, finding 16 proteins differentially expressed between males and females. Most of the identified proteins were involved in olfaction. High levels of pheromone binding proteins (PBP1 and PBP2) were found as expected in males, but also in female antennae, although females did not electrophysiologically respond to their own pheromone. General odorant binding proteins (GOBP1 and GOBP2) were preferentially expressed in females but high levels were also detected in males. The expression was remarkably high in both sexes along the complete photoperiod. A sensitive proteomic methodology was developed to identify antennal proteins.

Molecular identification and characterization of two new Lepidoptera chemoreceptors belonging to the Drosophila melanogaster OR83b family

In insect antennae, olfaction depends on olfactory receptors (ORs) that function through heterodimerization with an unusually highly conserved partner orthologue to the Drosophila melanogaster DOR83b. Here, we report the identification of two cDNAs encoding new DOR83b orthologues that represent the first members, although nonconventional, of the OR families of two noctuid crop pests, the cotton leafworm Spodoptera littoralis and the cabbage armyworm Mamestra brassicae. They both displayed high protein sequence conservation with previously identified DOR83b orthologues. Transcripts were abundantly detected in adult chemosensory organs as well as in fifth instar larvae heads. In adult antennae, the expression patterns of both genes revealed common features with other members of the OR83b subfamily: they appeared to be expressed at the bases of numerous olfactory sensilla belonging to different functional categories, suggesting that both receptors may be co-expressed with yet unidentified conventional ORs. Bioinformatic analyses predicted the occurrence of seven transmembrane domains and an unusual topology with intracellular N-termini and extracellular C-termini, extending to Lepidoptera the hypothesis of an inverted topology for DOR83b orthologues, demonstrated to date only in D. melanogaster.

Identification of candidate aldehyde oxidases from the silkworm Bombyx mori potentially involved in antennal pheromone degradation

Signal inactivation is a crucial step in the dynamic of olfactory process and involves various Odorant-Degrading Enzymes. In the silkworm Bombyx mori, one of the best models for studying olfaction in insects, the involvement of an antennal-specific aldehyde oxidase in the degradation of the sex pheromone component bombykal has been demonstrated over the three past decades by biochemical studies. However, the corresponding enzyme has never been characterized at the molecular level. Bioinformatic screening of B. mori genome and molecular approaches have been used to isolate several candidate sequences of aldehyde oxidases. Two interesting antennal-expressed genes have been further characterized and their putative functions are discussed in regard to their respective expression pattern and to our knowledge on aldehyde oxidase properties. Interestingly, one gene appeared as specifically expressed in the antennae of B. mori and associated in males with the bombykal-sensitive sensilla, strongly suggesting that it could encode for the previously biochemically characterized enzyme.

Molecular cloning and in Situ expression patterns of two new pheromone-binding proteins from the corn stemborer Sesamia nonagrioides

We describe the identification and characterization of two new cDNAs encoding pheromone-binding proteins (PBPs) from the male antennae of Sesamia nonagrioides, a species where no PBPs have been identified to date. Because PBPs are thought to participate in the first step of odor detection in a specific manner, we focused our investigation on this olfactory protein family using reverse transcription-polymerase chain reaction strategies. The deduced amino acid sequences of SnonPBP1 and SnonPBP2 revealed mature proteins of 142 and 143 amino acids, respectively, with six cysteine residues in conserved positions relative to other known PBPs. The alignment of the two mature S. nonagrioides PBPs with other noctuid PBPs showed high sequence identity (70-80%) with other full-length sequences from GenBank. Sequence identity between SnonPBP1 and SnonPBP2 was only 46%, suggesting that the two proteins belong to different classes of PBPs already described from the Noctuidae. Furthermore, analyses of expression patterns of SnonPBP1 and SnonPBP2 were performed by in situ hybridization on antennae of both sexes, and these studies revealed the expression of the two PBPs at the bases of olfactory sensilla (basiconica or trichodea) from both sexes. The possible binding properties of these two new PBPs are discussed according to their homologies with other known PBPs and S. nonagrioides pheromone components.

Microarray-based survey of a subset of putative olfactory genes in the mosquito Anopheles gambiae

Female Anopheles gambiae mosquitoes respond to odours emitted from humans in order to find a blood meal, while males are nectar feeders. This complex behaviour is controlled at several levels, but is probably initiated by the interaction of various molecules in the antennal sensilla. Important molecules in the early odour recognition events include odourant binding proteins (OBPs), which may be involved in odour molecule transport, odourant receptors (ORs) that are expressed in the chemosensory neurones and odour degrading enzymes (ODEs). To obtain a better understanding of the expression patterns of genes that may be involved in host odour reception in females, we generated a custom microarray to study their steady state mRNA levels in chemosensory tissues, antennae and palps. These results were supported by quantitative RT PCR. Our study detected several OBPs that are expressed at significantly higher levels in antennae and palps of females vs. males, while others showed the opposite expression pattern. Most OBPs are slightly down-regulated 24 h after blood feeding, but some, especially those with higher expression levels in males, are up-regulated in blood-fed females, suggesting a shift in blood-fed females from human host seeking to nectar feeding.

Molecular characterization and evolution of pheromone binding protein genes in Agrotis moths

Pheromone-binding proteins (PBPs) are soluble transporter proteins that increase the capture and the solubilization of pheromone molecules in the lymph surrounding the olfactory receptors. A polymerase chain reaction-based method was used to identify PBP genes in Agrotis species for an evolutionary genomic study of noctuid moth PBPs. From genomic DNA we determined the structure of different PBP genes in the two closely related species, Agrotis ipsilon and A. segetum. In all, we clearly identified four genes (Aips-1, Aips-2, Aseg-1 and Aseg-2) that represent two distinct PBP orthology groups. We found that the four genes have the same exon-intron structure and that they comprise three exons and two introns but differ in length mainly in the second intron. The three exons of Aseg-2 and Aips-2 have the same lengths but both intron 1 and intron 2 differ in length between the genes. In contrast, Aips-1 and Aseg-1 show dissimilarity only in the length of intron 2. Interestingly, introns 1 and 2 are inserted in the same positions in the Aips-1, Aips-2, Aseg-1 and Aseg-2 genes. These findings show that the Agrotis PBP genes have common ancestry and probably originate from gene duplication before the speciation of ipsilon and segetum. We found that expression of Aips-1/Aseg-1 and Aips-2/Aseg-2 is antennal-specific, but expression is not restricted to the male antennae.

Molecular cloning and bacterial expression of pheromone binding protein in the antennae of Helicoverpa armigera (Hübner)

A cDNA clone coding for pheromone binding protein was isolated from the antennae of Helicoverpa armigera by RT-PCR and (5'/3')-RACE technique. The full-length of H. armigera pheromone binding protein (HarmPBP) was 952 bp, possessing 162 amino acid residues including a signal peptide of 20 amino acids. Its predicted molecular weight and isoelectric point were 18.26 kDa and 5.23, respectively. This deduced amino acid sequence shared some common structural features with odorant-binding proteins from several moth species, including the six conserved cysteine motif, a typical characteristic of insect's odorant-binding proteins. Northern blot showed that HarmPBP is specifically expressed in the antennae of Helicoverpa armigera and more abundantly expressed in male than female. During the antennal development, HarmPBP is first expressed about 4 days prior to adult eclosion and rises to a plateau 2 days prior to adult eclosion. In order to obtain sufficient PBP for further determining its biochemical and physiological properties, a bacterical expression vector of PBP was constructed and successfully expressed in Escherichia coli. The recombinant PBP was shown to cross-react with an anti-PBP antiserum from Antheraea polyphemus. Polyclonal antibodies against HarmPBP were used to mark the distribution of the protein in olfactory sensilla. Very strong labeling was observed in the sensillum lymph of the hair lumen and of the sensillum-lymph cavity. In the male, HarmPBP is expressed in sensilla trichodea and not in sensilla basiconica, while in the female, it is expressed both in sensilla basiconica and sensilla trichodea.

Sexual dimorphic expression of putative antennal carrier protein genes in the malaria vector Anopheles gambiae

To obtain a better understanding of the olfactory processes that allow mosquitoes to identify human hosts, a molecular study has been performed to identify and characterize molecules in the olfactory signalling pathway of the African malaria vector Anopheles gambiae. Using cDNA libraries from antennae of females and males, a collection of cDNAs encoding odorant binding proteins and other novel antennal proteins were isolated and characterized, which represent various families of putative carrier proteins with homologues in other insects. Using filter array hybridizations and quantitative RT PCR, regulation and gender specificity of expression of these genes was investigated. Significant differences in steady-state levels of some of these putative carrier protein genes were detected between the sexes and after blood feeding in females.

Ligand binding to six recombinant pheromone-binding proteins of Antheraea polyphemus and Antheraea pernyi

Binding properties of six heterologously expressed pheromone-binding proteins (PBPs) identified in the silkmoths Antheraea polyphemus and Antheraea pernyi were studied using tritium-labelled pheromone components, ( E, Z)-6,11-hexadecadienyl acetate ((3)H-Ac1) and ( E, Z)-6,11-hexadecadienal ((3)H-Ald), common to both species. In addition, a known ligand of PBP and inhibitor of pheromone receptor cells, the tritium-labelled esterase inhibitor decyl-thio-1,1,1-trifluoropropanone ((3)H-DTFP), was tested. The binding of ligands was measured after native gel electrophoresis and cutting gel slices. In both species, PBP1 and PBP3 showed binding of (3)H-Ac1. In competition experiments with (3)H-Ac1 and the third unlabelled pheromone component, ( E, Z)-4,9-tetradecadienyl acetate (Ac2), the PBP1 showed preferential binding of Ac1, whereas PBP3 preferentially bound Ac2. The PBP2 of both species bound (3)H-Ald only. All of the six PBPs strongly bound (3)H-DTFP. Among unlabelled pheromone derivatives, alcohols were revealed to be the best competitors for (3)H-Ac1 and (3)H-Ald bound to PBPs. No pH influence was found for (3)H-Ac1 binding to, or its release from, the PBP3 of A. polyphemus and A. pernyi between pH 4.0 and pH 7.5. The data indicate binding preference of each of the three PBP-subtypes (1-3) for a specific pheromone component and support the idea that PBPs contribute to odour discrimination, although to a smaller extent than receptor activation.

Pheromone binding proteins of Epiphyas postvittana (Lepidoptera: Tortricidae) are encoded at a single locus

The light brown apple moth, Epiphyas postvittana (Tortricidae: Lepidoptera) uses a blend of (E)-11-tetradecenyl acetate and (E,E)-9,11-tetradecadienyl acetate as its sex pheromone. Odorant binding proteins, abundant in the antennae of male and female E. postvittana, were separated by native PAGE to reveal four major proteins with distinct mobilities. Microsequencing of their N-terminal residues showed that two were general odorant binding proteins (GOBPs) while two were pheromone binding proteins (PBPs). Full length cDNAs encoding these proteins were amplified using a combination of PCR and RACE-PCR. Sequence of the GOBPs revealed two genes (EposGOBP1, EposGOBP2), similar to orthologues in other species of Lepidoptera. Eleven cDNAs of the PBP gene were amplified, cloned and sequenced revealing two major phylogenetic clusters of PBP sequences differing by six amino acid substitutions. The position of the six amino acid differences on the protein was predicted by mapping onto the three-dimensional structure of PBP of Bombyx mori. All six substitutions were predicted to fall on the outside of the protein away from the inner pheromone binding pocket. One substitution does fall close to the putative dimerisation region of the protein (Ser63Thr). Expression of three of the cDNAs in a baculovirus expression system revealed that one class encodes an electrophoretically slow form (EposPBP1-12) while the other encodes a fast form (EposPBP1-2, EposPBP1-3). A native Western of these expressed proteins compared with antennal protein extracts demonstrated that PBP is also expressed in female antennae and that PBP may be present as a dimer as well as a monomer in E. postvittana. The fast and slow forms of EposPBP1 are allelic. Westerns on single antennal pair protein extracts and allele-specific PCR from genomic DNA both show a segregating pattern of inheritance in laboratory and wild populations. Radio labelled (E)-11-tetradecenyl acetate binds to both fast and slow PBP forms in gel assays. Taken together, the genetic and biochemical data do not support the hypothesis that these PBPs are specific for each component of the E. postvittana pheromone. However, duplication of this PBP locus in the future might allow such diversification to evolve, as observed in the other species.

Evolution of noctuid pheromone binding proteins: identification of PBP in the black cutworm moth, Agrotis ipsilon

Male black cutworm moths (Agrotis ipsilon, Lepidoptera, Noctuoidea, Noctuidae), which are attracted by a three-component pheromone blend ((Z)-7-dodecenyl acetate, Z7-12:Ac; (Z)-9-tetradecenyl acetate, Z9-14:Ac; (Z)-11-hexadecenyl acetate, Z11-16:Ac), express diverse antennal pheromone binding proteins (PBPs). Two PBP isoforms (Aips-1 and Aips-2) that show 46% identity were cloned from antennal cDNA of male A. ipsilon. The protein Aips-1 displays a high degree of identity (70-95%) with PBPs of other noctuiids, but shows only 42-65% identity with the PBPs of more phylogenetically distant species. The other protein, Aips-2, represents a distinct group of PBP that includes proteins from Sphingidae and Yponomeutidae. These differences observed suggest that each of the two PBPs may be tuned to a specific pheromone ligand.

Isolation of cDNA clones encoding putative odourant binding proteins from the antennae of the malaria-transmitting mosquito, Anopheles gambiae

One way of controlling disease transmission by blood-feeding mosquitoes is to reduce the frequency of insect-host interaction, thus reducing the probability of parasite transmission and re-infection. A better understanding of the olfactory processes responsible for allowing mosquitoes to identify human hosts is required in order to develop methods that will interfere with host seeking. We have therefore initiated a molecular approach to isolate and characterize the genes and their products that are involved in the olfactory recognition pathway of the mosquito Anopheles gambiae, which is the main malaria vector in sub-Saharan Africa. We report here the isolation and preliminary characterization of several cDNAs from male and female A. gambiae antennal libraries that encode putative odourant binding proteins. Their conceptual translation products show extensive sequence similarity to known insect odourant binding proteins (OBPs)/pheromone binding proteins (PBPs), especially to those of D. melanogaster. The A. gambiae OBPs described here are expressed in the antennae of both genders, and some of the A. gambiae OBP genes are well conserved in other disease-transmitting mosquito species, such as Aedes aegypti and Culex quinquefasciatus.

A comparative study of odorant binding protein genes: differential expression of the PBP1-GOBP2 gene cluster inManduca sexta(Lepidoptera) and the organization of OBP genes inDrosophila melanogaster(Diptera)

Insects discriminate odors using sensory organs called olfactory sensilla, which display a wide range of phenotypes. Sensilla express ensembles of proteins, including odorant binding proteins (OBPs), olfactory receptors (ORs) and odor degrading enzymes (ODEs); odors are thought to be transported to ORs by OBPs and subsequently degraded by ODEs. These proteins belong to multigene families. The unique combinatorial expression of specific members of each of these gene families determines, in part, the phenotype of a sensillum and what odors it can detect. Furthermore, OBPs, ORs and ODEs are expressed in different cell types, suggesting the need for cell–cell communication to coordinate their expression. This report examines the OBP gene family. In Manduca sexta, the genes encoding PBP1Msex and GOBP2Msex are sequenced, shown to be adjacent to one another, and characterized together with OBP gene structures of other lepidoptera and Drosophila melanogaster. Expression of PBP1Msex, GOBP1Msex and GOBP2Msex is characterized in adult male and female antenna and in larval antenna and maxilla. The genomic organization of 25 D. melanogaster OBPs are characterized with respect to gene locus, gene cluster, amino acid sequence similarity, exon conservation and proximity to OR loci, and their sequences are compared with 14 M. sexta OBPs. Sensilla serve as portals of important behavioral information, and genes supporting sensilla function are presumably under significant evolutionary selective pressures. This study provides a basis for studying the evolution of the OBP gene family, the regulatory mechanisms governing the coordinated expression of OBPs, ORs and ODEs, and the processes that determine specific sensillum phenotypes.

Identity and expression pattern of chemosensory proteins in Heliothis virescens (Lepidoptera, Noctuidae)

Analyzing the chemosensory organs of the moth Heliothis virescens, three proteins belonging to the family of insect chemosensory proteins (CSPs) have been cloned; they are called HvirCSP1, HvirCSP2 and HvirCSP3. The HvirCSPs show about 50% identity between each other and 30-76% identity to CSPs from other species. Overall, they are rather hydrophilic proteins but include a conserved hydrophobic motif. Tissue distribution and temporal expression pattern during the last pupal stages were assessed by Northern blots. HvirCSP mRNAs were detected in various parts of the adult body with a particular high expression level in legs. The expression of HvirCSP1 in legs started early during adult development, in parallel with the appearance of the cuticle. HvirCSP1 mRNA was detectable five days before eclosion (day E-5), increased dramatically on day E-3 and remained at high level into adult life. The tissue distribution and the time course of appearance of HvirCSPs are in agreement with a possible role in contact chemosensation.

Revisiting the specificity of Mamestra brassicae and Antheraea polyphemus pheromone-binding proteins with a fluorescence binding assay

Pheromone-binding proteins (PBPs), located in the sensillum lymph of pheromone-responsive antennal hairs, are thought to transport the hydrophobic pheromones to the chemosensory membranes of olfactory neurons. It is currently unclear what role PBPs may play in the recognition and discrimination of species-specific pheromones. We have investigated the binding properties and specificity of PBPs from Mamestra brassicae (MbraPBP1), Antheraea polyphemus (ApolPBP1), Bombyx mori (BmorPBP), and a hexa-mutant of MbraPBP1 (Mbra1-M6), mutated at residues of the internal cavity to mimic that of BmorPBP, using the fluorescence probe 1-aminoanthracene (AMA). AMA binds to MbraPBP1 and ApolPBP1, however, no binding was observed with either BmorPBP or Mbra1-M6. The latter result indicates that relatively limited modifications to the PBP cavity actually interfere with AMA binding, suggesting that AMA binds in the internal cavity. Several pheromones are able to displace AMA from the MbraPBP1- and ApolPBP1-binding sites, without, however, any evidence of specificity for their physiologically relevant pheromones. Moreover, some fatty acids are also able to compete with AMA binding. These findings bring into doubt the currently held belief that all PBPs are specifically tuned to distinct pheromonal compounds.

Characterization and cloning of a Tenebrio molitor hemolymph protein with sequence similarity to insect odorant-binding proteins

The yellow mealworm beetle, Tenebrio molitor, produces a number of moderately abundant low molecular weight hemolymph proteins ( approximately 12 kDa) which behave in a similar manner during purification and share antigenic epitopes. The cDNA sequence of the major component (THP12) was determined and the deduced protein sequence was found to be similar to those of insect odorant-binding proteins. Southern blot analysis suggests that at least some of the diversity in this family of proteins is encoded at the gene level. Both northern and western blot analysis indicate that THP12 is present in a variety of developmental stages and both sexes. THP12 was originally classified as an antifreeze protein, but the lack of antifreeze activity in the recombinant protein, as well as the clear separation of the antifreeze activity from THP12 following HPLC purification, has ruled out this function. The abundance of THP12, the similarity of THP12 to insect odorant-binding proteins, and the presence of hydrophobic cavities inside the protein (Rothemund et al., A new class of hexahelical insect proteins revealed as putative carriers of small hydrophobic ligands. Structure, 7 (1999) 1325-1332.) suggest that THP12 may function to carry non-water soluble compounds in the hemolymph. THP12 is also similar, particularly in structurally important regions, to other insect proteins from non-sensory tissues, suggesting the existence of a large family of carrier proteins which may perform diverse functions throughout the insect.

Purification and molecular cloning of chemosensory proteins from Bombyx mori

Soluble low molecular weight acidic proteins are suspected to transport stimulus molecules to the sensory neurons within insect sensilla. From the antennae of Bombyx mori, we have purified and sequenced a protein (BmorCSP1) bearing sequence similarity to a class of soluble chemosensory proteins recently discovered in several orders of insects. Based on its N-terminal sequence, the cDNA encoding this protein has been amplified and cloned. Differential screening of a B. mori antennal cDNA library led to the identification of a second gene encoding a related protein (BmorCSP2), sharing 35-40% identity to BmorCSP1 and chemosensory proteins from other species. The predicted secondary structures of moth's, chemosensory proteins comprise alpha-helical foldings at conserved positions and a reduced hydrophobicity with respect to this novel family of chemosensory proteins.

High level expression of "male specific" pheromone binding proteins (PBPs) in the antennae of female noctuiid moths

Pheromone Binding Proteins (PBPs) are one branch of a multigene family of lepidopteran Odorant Binding Proteins (OBPs) that are known for their relatively high levels of expression in male antennae. However, PBP expression has been observed at low levels in female antennae of the Saturniidae, Bombycidae and Lymantriidae, and at relatively high levels in members of the Noctuiidae. The function of female PBP expression is unclear, as female lepidoptera are consistently noted for their failure to respond physiologically or behaviorally to sex-pheromone. In this study, the sexual dimorphism of PBP expression was examined in the noctuiid moths Helicoverpa zea, Heliothis virescens and Spodoptera frugiperda. A PBP cDNA clone was isolated from female H. zea, PBP-Hzea(f). Northern blot analysis indicated relatively high levels of PBP-Hzea(f) expression in both male and female antennae, though females consistently expressed about 50% that of males. Western blot analysis of male and female PBP expression supported these relative differences. Immunocytochemical analysis indicates discrete expression localized beneath olfactory sensilla of both male and female antennae. These results suggest female noctuiids possess the biochemistry to detect at least components of their sex-pheromone. Alternatively, these results may suggest that PBPs have a more general function in noctuiids, possibly reflecting behavioral and life history differences that distinguish this the Noctuiidae from other Lepidopteran families.

Three pheromone-binding proteins in olfactory sensilla of the two silkmoth species Antheraea polyphemus and Antheraea pernyi

Females of the sibling silkmoth species Antheraea polyphemus and A. pernyi use the same three sex pheromone components in different ratios to attract conspecific males. Accordingly, the sensory hairs on the antennae of males contain three receptor cells sensitive to each of the pheromone components. In agreement with the number of pheromones used, three different pheromone-binding proteins (PBPs) could be identified in pheromone-sensitive hairs of both species by combining biochemical and molecular cloning techniques. MALDI-TOF MS of sensillum lymph droplets from pheromone-sensitive sensilla trichodea of male A. polyphemus revealed the presence of three major peaks with m/z of 15702, 15752 and 15780 and two minor peaks of m/z 15963 and 15983. In Western blots with four antisera raised against different silkmoth odorant-binding proteins, immunoreactivity was found only with an anti-(Apol PBP) serum. Free-flow IEF, ion-exchange chromatography and Western blot analyses revealed at least three anti-(Apol PBP) immunoreactive proteins with pI values between 4.4 and 4.7. N-Terminal sequencing of these three proteins revealed two proteins (Apol PBP1a and Apol PBP1b) identical in the first 49 amino acids to the already known PBP (Apol PBP1) [Raming, K. , Krieger, J. & Breer, H. (1989) FEBS Lett. 256, 2215-2218] and a new PBP having only 57% identity with this amino-acid region. Screening of antennal cDNA libraries with an oligonucleotide probe corresponding to the N-terminal end of the new A. polyphemus PBP, led to the discovery of full length clones encoding this protein in A. polyphemus (Apol PBP3) and in A. pernyi (Aper PBP3). By screening the antennal cDNA library of A. polyphemus with a digoxigenin-labelled A. pernyi PBP2 cDNA [Krieger, J., Raming, K. & Breer, H. (1991) Biochim. Biophys. Acta 1088, 277-284] a homologous PBP (Apol PBP2) was cloned. Binding studies with the two main pheromone components of A. polyphemus and A. pernyi, the (E,Z)-6, 11-hexadecadienyl acetate (AC1) and the (E,Z)-6,11-hexadecadienal (ALD), revealed that in A. polyphemus both Apol PBP1a and the new Apol PBP3 bound the 3H-labelled acetate, whereas no binding of the 3H-labelled aldehyde was found. In A. pernyi two PBPs from sensory hair homogenates showed binding affinity for the AC1 (Aper PBP1) and the ALD (Aper PBP2), respectively.

Disulfide structure of the pheromone binding protein from the silkworm moth, Bombyx mori

Disulfide bond formation is the only known posttranslational modification of insect pheromone binding proteins (PBPs). In the PBPs from moths (Lepidoptera), six cysteine residues are highly conserved at positions 19, 50, 54, 97, 108 and 117, but to date nothing is known about their respective linkage or redox status. We used a multiple approach of enzymatic digestion, chemical cleavage, partial reduction with Tris-(2-carboxyethyl)phosphine, followed by digestion with endoproteinase Lys-C to determine the disulfide connectivity in the PBP from Bombyx mori (BmPBP). Identification of the reaction products by on-line liquid chromatography-electrospray ionization mass spectrometry (LC/ESI-MS) and protein sequencing supported the assignment of disulfide bridges at Cys-19-Cys-54, Cys-50-Cys-108 and Cys-97-Cys-117. The disulfide linkages were identical in the protein obtained by periplasmic expression in Escherichia coli and in the native BmPBP.

Diversity of odourant binding proteins revealed by an expressed sequence tag project on male Manduca sexta moth antennae

A small expressed sequence tag (EST) project generating 506 ESTs from 375 cDNAs was undertaken on the antennae of male Manduca sexta moths in an effort to discover olfactory receptor proteins. We encountered several clones that encode apparent transmembrane proteins; however, none is a clear candidate for an olfactory receptor. Instead we found a greater diversity of odourant binding proteins (OBPs) than previously known in moth antennae, raising the number known for M. sexta from three to seven. Together with evidence of seventeen members of the family from the Drosophila melanogaster genome project, our results suggest that insects may have many tens of OBPs expressed in subsets of the chemosensory sensilla on their antennae. These results support a model for insect olfaction in which OBPs selectively transport and present odourants to transmembrane olfactory receptors. We also found five members of a family of shorter proteins, named sensory appendage proteins (SAPs), that might also be involved in odourant transport. This small EST project also revealed several candidate odourant degrading enzymes including three P450 cytochromes, a glutathione S-transferase and a uridine diphosphate (UDP) glucosyltransferase. Several first insect homologues of proteins known from vertebrates, the nematode Caenorhabditis elegans, yeast and bacteria were encountered, and most have now also been detected by the large D. melanogaster EST project. Only thriteen entirely novel proteins were encountered, some of which are likely to be cuticle proteins.