Multiple amino acid changes are responsible for the shift of tuning breadth along the evolutionary trajectory of a moth pheromone receptor

Sex pheromone recognition is essential for mating in many insects and plays a major role in maintaining reproductive barriers. A previous study from our lab reported the evolutionary history of the pheromone receptor OR5 in Spodoptera moths. Using heterologous expression in Xenopus oocytes and site-directed mutagenesis, we found that eight amino acid substitutions were sufficient to recapitulate the evolution from an ancestral broadly-tuned to a highly specific receptor. Here, we confirmed this result using expression in Drosophila olfactory neurons. This further confirmed that multiple amino acid changes explain the shift in tuning breadth of Spodoptera OR5 during evolution.

A tale of two copies: Evolutionary trajectories of moth pheromone receptors

Pheromone communication is an essential component of reproductive isolation in animals. As such, evolution of pheromone signaling can be linked to speciation. For example, the evolution of sex pheromones is thought to have played a major role in the diversification of moths. In the crop pests Spodoptera littoralis and S. litura, the major component of the sex pheromone blend is (Z,E)-9,11-tetradecadienyl acetate, which is lacking in other Spodoptera species. It indicates that a major shift occurred in their common ancestor. It has been shown recently in S. littoralis that this compound is detected with high specificity by an atypical pheromone receptor, named SlitOR5. Here, we studied its evolutionary history through functional characterization of receptors from different Spodoptera species. SlitOR5 orthologs in S. exigua and S. frugiperda exhibited a broad tuning to several pheromone compounds. We evidenced a duplication of OR5 in a common ancestor of S. littoralis and S. litura and found that in these two species, one duplicate is also broadly tuned while the other is specific to (Z,E)-9,11-tetradecadienyl acetate. By using ancestral gene resurrection, we confirmed that this narrow tuning evolved only in one of the two copies issued from the OR5 duplication. Finally, we identified eight amino acid positions in the binding pocket of these receptors whose evolution has been responsible for narrowing the response spectrum to a single ligand. The evolution of OR5 is a clear case of subfunctionalization that could have had a determinant impact in the speciation process in Spodoptera species.

First chromosome scale genomes of ithomiine butterflies (Nymphalidae: Ithomiini): Comparative models for mimicry genetic studies

The ithomiine butterflies (Nymphalidae: Danainae) represent the largest known radiation of Müllerian mimetic butterflies. They dominate by number the mimetic butterfly communities, which include species such as the iconic neotropical Heliconius genus. Recent studies on the ecology and genetics of speciation in Ithomiini have suggested that sexual pheromones, colour pattern and perhaps hostplant could drive reproductive isolation. However, no reference genome was available for Ithomiini, which has hindered further exploration on the genetic architecture of these candidate traits, and more generally on the genomic patterns of divergence. Here, we generated high-quality, chromosome-scale genome assemblies for two Melinaea species, M. marsaeus and M. menophilus, and a draft genome of the species Ithomia salapia. We obtained genomes with a size ranging from 396 to 503 Mb across the three species and scaffold N50 of 40.5 and 23.2 Mb for the two chromosome-scale assemblies. Using collinearity analyses we identified massive rearrangements between the two closely related Melinaea species. An annotation of transposable elements and gene content was performed, as well as a specialist annotation to target chemosensory genes, which is crucial for host plant detection and mate recognition in mimetic species. A comparative genomic approach revealed independent gene expansions in ithomiines and particularly in gustatory receptor genes. These first three genomes of ithomiine mimetic butterflies constitute a valuable addition and a welcome comparison to existing biological models such as Heliconius, and will enable further understanding of the mechanisms of adaptation in butterflies.

Activation of pheromone-sensitive olfactory neurons by plant volatiles in the moth Agrotis ipsilon does not occur at the level of the pheromone receptor protein

In moths, mate finding relies on female-emitted sex pheromones that the males have to decipher within a complex environmental odorant background. Previous studies have shown that interactions of both sex pheromones and plant volatiles can occur in the peripheral olfactory system, and that some plant volatiles can activate the pheromone-specific detection pathway. In the noctuid moth Agrotis ipsilon, plant volatiles such as heptanal activate the receptor neurons tuned to the pheromone component (Z)7-12:OAc. However, the underlying mechanisms remain totally unknown. Following the general rule that states that one olfactory receptor neuron usually expresses only one type of receptor protein, a logic explanation would be that the receptor protein expressed in (Z)7-12:OAc-sensitive neurons recognizes both pheromone and plant volatiles. To test this hypothesis, we first annotated odorant receptor genes in the genome of A. ipsilon and we identified a candidate receptor putatively tuned to (Z)7-12:OAc, named AipsOR3. Then, we expressed it in Drosophila olfactory neurons and determined its response spectrum to a large panel of pheromone compounds and plant volatiles. Unexpectedly, the receptor protein AipsOR3 appeared to be very specific to (Z)7-12:OAc and was not activated by any of the plant volatiles tested, including heptanal. We also found that (Z)7-12:OAc responses of Drosophila neurons expressing AipsOR3 were not affected by a background of heptanal. As the Drosophila olfactory sensilla that house neurons in which AipsOR3 was expressed contain other olfactory proteins – such as odorant-binding proteins – that may influence its selectivity, we also expressed AipsOR3 in Xenopus oocytes and confirmed its specificity and the lack of activation by plant volatiles. Altogether, our results suggest that a still unknown second odorant receptor protein tuned to heptanal and other plant volatiles is expressed in the (Z)7-12:OAc-sensitive neurons of A. ipsilon.

Spodoptera littoralis genome mining brings insights on the dynamic of expansion of gustatory receptors in polyphagous noctuidae

The bitter taste, triggered via gustatory receptors, serves as an important natural defense against the ingestion of poisonous foods in animals, and the increased host breadth is usually linked to an increase in the number of gustatory receptor genes. This has been especially observed in polyphagous insect species, such as noctuid species from the Spodoptera genus. However, the dynamic and physical mechanisms leading to these gene expansions and the evolutionary pressures behind them remain elusive. Among major drivers of genome dynamics are the transposable elements but, surprisingly, their potential role in insect gustatory receptor expansion has not been considered yet. In this work, we hypothesized that transposable elements and possibly positive selection would be involved in the highly dynamic evolution of gustatory receptor in Spodoptera spp. We first sequenced de novo the full 465 Mb genome of S. littoralis, and manually annotated the main chemosensory genes, including a large repertoire of 373 gustatory receptor genes (including 19 pseudogenes). We also improved the completeness of S. frugiperda and S. litura gustatory receptor gene repertoires. Then, we annotated transposable elements and revealed that a particular category of class I retrotransposons, the SINE transposons, was significantly enriched in the vicinity of gustatory receptor gene clusters, suggesting a transposon-mediated mechanism for the formation of these clusters. Selection pressure analyses indicated that positive selection within the gustatory receptor gene family is cryptic, only 7 receptors being identified as positively selected. Altogether, our data provide a new good quality Spodoptera genome, pinpoint interesting gustatory receptor candidates for further functional studies and bring valuable genomic information on the mechanisms of gustatory receptor expansions in polyphagous insect species.

Pheromone Receptor Knock-Out Affects Pheromone Detection and Brain Structure in a Moth

Sex pheromone receptors are crucial in insects for mate finding and contribute to species premating isolation. Many pheromone receptors have been functionally characterized, especially in moths, but loss of function studies are rare. Notably, the potential role of pheromone receptors in the development of the macroglomeruli in the antennal lobe (the brain structures processing pheromone signals) is not known. Here, we used CRISPR-Cas9 to knock-out the receptor for the major component of the sex pheromone of the noctuid moth Spodoptera littoralis, and investigated the resulting effects on electrophysiological responses of peripheral pheromone-sensitive neurons and on the structure of the macroglomeruli. We show that the inactivation of the receptor specifically affected the responses of the corresponding antennal neurons did not impact the number of macroglomeruli in the antennal lobe but reduced the size of the macroglomerulus processing input from neurons tuned to the main pheromone component. We suggest that this mutant neuroanatomical phenotype results from a lack of neuronal activity due to the absence of the pheromone receptor and potentially reduced neural connectivity between peripheral and antennal lobe neurons. This is the first evidence of the role of a moth pheromone receptor in macroglomerulus development and extends our knowledge of the different functions odorant receptors can have in insect neurodevelopment.

Description of Chemosensory Genes in Unexplored Tissues of the Moth Spodoptera littoralis

Illumina-based transcriptome sequencing of chemosensory organs has become a standard in deciphering the molecular bases of chemical senses in insects, especially in non-model species. A plethora of antennal transcriptomes is now available in the literature, describing large sets of chemosensory receptors and binding proteins in a diversity of species. However, little is still known on other organs such as mouthparts, legs and ovipositors, which are also known to carry chemosensory sensilla. This is the case of the noctuid Spodoptera littoralis, which has been established as a model insect species in molecular chemical ecology thanks to the description of many—but not all—chemosensory genes. To fulfill this gap, we present here an unprecedented transcriptomic survey of chemosensory tissues in this species. RNAseq from male and female proboscis, labial palps, legs and female ovipositors allowed us to annotate 115 putative chemosensory gene transcripts, including 30 novel genes in this species. Especially, we doubled the number of candidate gustatory receptor transcripts described in this species. We also evidenced ectopic expression of many chemosensory genes. Remarkably, one third of the odorant receptors were found to be expressed in the proboscis. With a total of 196 non-overlapping chemosensory genes annotated, the S. littoralis repertoire is one of the most complete in Lepidoptera. We further evaluated the expression of transcripts between males and females, pinpointing sex-specific transcripts. We identified five female-specific transcripts, including one odorant receptor, one gustatory receptor, one ionotropic receptor and one odorant-binding protein, and one male-specific gustatory receptor. Such sex-biased expression suggests that these transcripts participate in sex-specific behaviors, such as host choice for oviposition in females and/or mating partner recognition in both sexes.

Sublethal Exposure Effects of the Neonicotinoid Clothianidin Strongly Modify the Brain Transcriptome and Proteome in the Male Moth Agrotis ipsilon

Simple Summary

Insect pest management relies mainly on neurotoxic insecticides, including neonicotinoids such as clothianidin. Low doses of insecticides can stimulate various life traits in target pest insects, whereas negative effects are expected. We recently showed that treatments with different low doses of clothianidin could modify behavioral and neuronal sex pheromone responses in the male moth, Agrotis ipsilon. In this study, we showed that clothianidin disrupted 1229 genes and 49 proteins at the molecular level, including numerous enzymes of detoxification and neuronal actors, which could explain the acclimatization in pest insects to the insecticide-contaminated environment.

Abstract

Insect pest management relies mainly on neurotoxic insecticides, including neonicotinoids such as clothianidin. The residual accumulation of low concentrations of these insecticides can have positive effects on target pest insects by enhancing various life traits. Because pest insects often rely on sex pheromones for reproduction and olfactory synaptic transmission is cholinergic, neonicotinoid residues could indeed modify chemical communication. We recently showed that treatments with low doses of clothianidin could induce hormetic effects on behavioral and neuronal sex pheromone responses in the male moth, Agrotis ipsilon. In this study, we used high-throughput RNAseq and proteomic analyses from brains of A. ipsilon males that were intoxicated with a low dose of clothianidin to investigate the molecular mechanisms leading to the observed hormetic effect. Our results showed that clothianidin induced significant changes in transcript levels and protein quantity in the brain of treated moths: 1229 genes and 49 proteins were differentially expressed upon clothianidin exposure. In particular, our analyses highlighted a regulation in numerous enzymes as a possible detoxification response to the insecticide and also numerous changes in neuronal processes, which could act as a form of acclimatization to the insecticide-contaminated environment, both leading to enhanced neuronal and behavioral responses to sex pheromone.

A novel lineage of candidate pheromone receptors for sex communication in moths

Sex pheromone receptors (PRs) are key players in chemical communication between mating partners in insects. In the highly diversified insect order Lepidoptera, male PRs tuned to female-emitted type I pheromones (which make up the vast majority of pheromones identified) form a dedicated subfamily of odorant receptors (ORs). Here, using a combination of heterologous expression and in vivo genome editing methods, we bring functional evidence that at least one moth PR does not belong to this subfamily but to a distantly related OR lineage. This PR, identified in the cotton leafworm Spodoptera littoralis, is highly expressed in male antennae and is specifically tuned to the major sex pheromone component emitted by females. Together with a comprehensive phylogenetic analysis of moth ORs, our functional data suggest two independent apparitions of PRs tuned to type I pheromones in Lepidoptera, opening up a new path for studying the evolution of moth pheromone communication.

Molecular Characterization of MbraOR16, a Candidate Sex Pheromone Receptor in Mamestra brassicae (Lepidoptera: Noctuidae)

Sex pheromone communication in Lepidoptera has long been a valuable model system for studying fundamental aspects of olfaction and its study has led to the establishment of environmental-friendly pest control strategies. The cabbage moth, Mamestra brassicae (Linnaeus) (Lepidoptera: Noctuidae), is a major pest of Cruciferous vegetables in Europe and Asia. Its sex pheromone has been characterized and is currently used as a lure to trap males; however, nothing is known about the molecular mechanisms of sex pheromone reception in male antennae. Using homology cloning and rapid amplification of cDNA ends-PCR strategies, we identified the first candidate pheromone receptor in this species. The transcript was specifically expressed in the antennae with a strong male bias. In situ hybridization experiments within the antennae revealed that the receptor-expressing cells were closely associated with the olfactory structures, especially the long trichoid sensilla known to be pheromone-sensitive. The deduced protein is predicted to adopt a seven-transmembrane structure, a hallmark of insect odorant receptors, and phylogenetically clustered in a clade that grouped a majority of the Lepidoptera pheromone receptors characterized to date. Taken together, our data support identification of a candidate pheromone receptor and provides a basis for better understanding how this species detects a signal critical for reproduction.

Heritable genome editing with CRISPR/Cas9 induces anosmia in a crop pest moth

Lepidoptera suffer critical lack of genetic tools and heritable genome edition has been achieved only in a few model species. Here we demonstrate that the CRISPR/Cas9 system is highly efficient for genome editing in a non-model crop pest Lepidoptera, the noctuid moth Spodoptera littoralis. We knocked-out the olfactory receptor co-receptor Orco gene to investigate its function in Lepidoptera olfaction. We find that 89.6% of the injected individuals carried Orco mutations, 70% of which transmitted them to the next generation. CRISPR/Cas9-mediated Orco knockout caused defects in plant odor and sex pheromone olfactory detection in homozygous individuals. Our work genetically defines Orco as an essential OR partner for both host and mate detection in Lepidoptera, and demonstrates that CRISPR/Cas9 is a simple and highly efficient genome editing technique in noctuid pests opening new routes for gene function analysis and the development of novel pest control strategies.

Candidate chemosensory genes in female antennae of the noctuid moth Spodoptera littoralis

Chemical senses are crucial for all organisms to detect various environmental information. Different protein families, expressed in chemosensory organs, are involved in the detection of this information, such as odorant-binding proteins, olfactory and gustatory receptors, and ionotropic receptors. We recently reported an Expressed Sequence Tag (EST) approach on male antennae of the noctuid moth, Spodoptera littoralis, with which we could identify a large array of chemosensory genes in a species for which no genomic data are available.

Here we describe a complementary EST project on female antennae in the same species. 18,342 ESTs were sequenced and their assembly with our previous male ESTs led to a total of 13,685 unigenes, greatly improving our description of the S. littoralis antennal transcriptome. Gene ontology comparison between male and female data suggested a similar complexity of antennae of both sexes. Focusing on chemosensation, we identified 26 odorant-binding proteins, 36 olfactory and 5 gustatory receptors, expressed in the antennae of S. littoralis. One of the newly identified gustatory receptors appeared as female-enriched. Together with its atypical tissue-distribution, this suggests a role in oviposition. The compilation of male and female antennal ESTs represents a valuable resource for exploring the mechanisms of olfaction in S. littoralis.

Functional characterization of a sex pheromone receptor in the pest moth Spodoptera littoralis by heterologous expression in Drosophila

Moth sex pheromone communication is recognised as a long-standing model for insect olfaction studies, and a widespread knowledge has been accumulated on this subject thanks to numerous chemical, electrophysiological and behavioural studies. A key step has been the identification of candidate sex pheromone receptors, opening new routes to understanding the specificity and sensitivity of this communication system, but only few of these receptors have as yet been functionally characterised. In this context, we aim at unravelling the molecular bases of pheromone reception in the noctuid moth Spodoptera littoralis. Taking advantage of a collection of antennal-expressed sequence tags, we previously identified three fragments of candidate pheromone receptors in this species. Here, we report full-length cloning of one of these receptors, named SlitOR6. Both sequence and expression pattern analyses were consistent with its annotation as a pheromone receptor, which we further confirmed by functional characterization. Using Drosophila antennae as a heterologous expression system, we identified a single component of the pheromone blend of S. littoralis, (Z,E)-9,12-tetradecadienyl acetate, as the ligand of SlitOR6. Two strategies were employed: (i) expressing SlitOR6 in the majority of Drosophila olfactory neurons, in addition to endogenous receptors, and monitoring the responses to pheromone stimuli by electroantennography; (ii) replacing the Drosophila pheromone receptor OR67d with SlitOR6 and monitoring the response by single sensillum recordings. Results were fully congruent and responses to (Z,E)-9,12-tetradecadienyl acetate were highly specific in both heterologous systems. This approach appears to be efficient and reliable for studying moth pheromone receptors in an in vivo context.

An Expressed Sequence Tag collection from the male antennae of the Noctuid moth Spodoptera littoralis: a resource for olfactory and pheromone detection research

BACKGROUND

Nocturnal insects such as moths are ideal models to study the molecular bases of olfaction that they use, among examples, for the detection of mating partners and host plants. Knowing how an odour generates a neuronal signal in insect antennae is crucial for understanding the physiological bases of olfaction, and also could lead to the identification of original targets for the development of olfactory-based control strategies against herbivorous moth pests. Here, we describe an Expressed Sequence Tag (EST) project to characterize the antennal transcriptome of the noctuid pest model, Spodoptera littoralis, and to identify candidate genes involved in odour/pheromone detection.

RESULTS

By targeting cDNAs from male antennae, we biased gene discovery towards genes potentially involved in male olfaction, including pheromone reception. A total of 20760 ESTs were obtained from a normalized library and were assembled in 9033 unigenes. 6530 were annotated based on BLAST analyses and gene prediction software identified 6738 ORFs. The unigenes were compared to the Bombyx mori proteome and to ESTs derived from Lepidoptera transcriptome projects. We identified a large number of candidate genes involved in odour and pheromone detection and turnover, including 31 candidate chemosensory receptor genes, but also genes potentially involved in olfactory modulation.

CONCLUSIONS

Our project has generated a large collection of antennal transcripts from a Lepidoptera. The normalization process, allowing enrichment in low abundant genes, proved to be particularly relevant to identify chemosensory receptors in a species for which no genomic data are available. Our results also suggest that olfactory modulation can take place at the level of the antennae itself. These EST resources will be invaluable for exploring the mechanisms of olfaction and pheromone detection in S. littoralis, and for ultimately identifying original targets to fight against moth herbivorous pests.

Cloning and expression pattern of a putative octopamine/tyramine receptor in antennae of the noctuid moth Mamestra brassicae

In insects, biogenic amines have been shown to play an important role in olfactory plasticity. In a first attempt to decipher the underlying molecular mechanisms, we report the molecular cloning and precise expression pattern of a newly identified octopamine/tyramine-receptor-encoding gene in the antennae of the noctuid moth Mamestra brassicae (MbraOAR/TAR). A full-length cDNA has been obtained through homology cloning in combination with rapid amplification of cDNA ends/polymerase chain reaction; the deduced protein exhibits high identities with previously identified octopamine/tyramine receptors in other moths. In situ hybridization within the antennae has revealed that MbraOAR/TAR is expressed at the bases of both pheromone-sensitive and non-sensitive olfactory sensilla and in cells with a neurone-like shape. In accordance with previous physiological studies that have revealed a role of biogenic amines in the electrical activity of the receptor neurones, our results suggest that biogenic amines (either octopamine or tyramine) target olfactory receptor neurones to modulate olfactory coding as early as the antennal level.

An antennal circadian clock and circadian rhythms in peripheral pheromone reception in the moth Spodoptera littoralis

Circadian rhythms are observed in mating behaviors in moths: females emit sex pheromones and males are attracted by these pheromones in rhythmic fashions. In the moth Spodoptera littoralis, we demonstrated the occurrence of a circadian oscillator in the antenna, the peripheral olfactory organ. We identified different clock genes, period (per), cryptochrome1 (cry1) and cryptochrome2 (cry2), in this organ. Using quantitative real-time PCR (qPCR), we found that their corresponding transcripts cycled circadianly in the antenna as well as in the brain. Electroantennogram (EAG) recordings over 24 h demonstrated for the first time a circadian rhythm in antennal responses of a moth to sex pheromone. qPCR showed that out of one pheromone-binding protein (PBP), one olfactory receptor (OR), and one odorant-degrading enzyme (ODE), all putatively involved in the pheromone reception, only the ODE transcript presented a circadian rhythm that may be related to rhythms in olfactory signal resolution. Peripheral or central circadian clock control of olfaction is then discussed in light of recent data.

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.

P450 and P450 reductase cDNAs from the moth Mamestra brassicae: cloning and expression patterns in male antennae

The involvement of cytochrome P450 (CYP) enzymes in olfaction has been demonstrated in vertebrates over the past decade. In insects, these enzymes are well known for their role in biosynthesis of endogenous compounds as well as xenobiotic metabolism, but the presence of olfactory cytochrome P450s was poorly investigated. Using a PCR-based strategy, we have isolated cDNAs of two new microsomal P450s from the antennae of the cabbage armyworm Mamestra brassicae, CYP9A13 and CYP4G20 of two new microsomal P450s, as well as their red-ox partner, the cytochrome P450 reductase (CPR). Their distribution through the body and their cellular localization within the antennae were studied by RT-PCR and in situ hybridization. The three genes are strongly expressed in some sensory units of the antennae, the sensilla trichodea, which are tuned to odorants detection. The putative functions of the corresponding enzymes are discussed in regard to their respective expression patterns and to our knowledge on olfactory P450 metabolism in mammals.

Putative odorant-degrading esterase cDNA from the moth Mamestra brassicae: cloning and expression patterns in male and female antennae

An esterase cDNA was isolated from the cabbage armyworm Mamestra brassicae antennae by PCR strategy. The full-length cDNA, designated as Mbra-EST, contains a 1638 bp open reading frame encoding a predicted protein of 546 amino acids. This predicted protein presents the structural characteristics of known insect carboxyl-esterases, in particular the Ser-His-Glu catalytic triad. The expression pattern of the gene was studied by RT-PCR, Northern-blot and in situ hybridization. The ribosomal protein rpL8 gene from M. brassicae was also cloned to obtain a normalized tool for the comparative gene expression studies. Mbra-EST transcripts are specifically expressed in the antennae of males and females and in the proboscis of males. In antennae of both sexes, expression is restricted to the olfactory sensilla trichodea, suggesting a role in degradation of odorant acetate compounds, such as pheromones as well as plant volatile acetate components.

Identification and molecular cloning of putative odorant-binding proteins from the American palm weevil, Rhynchophorus palmarum L

We have identified and cloned the cDNAs encoding two odorant-binding proteins (OBPs) from the American palm weevil (APW) Rhynchophorus palmarum (Coleoptera, Curculionidae). Degenerate primers were designed from the N-terminal sequences and were used in polymerase chain reaction (PCR) in order to obtain full-length sequences in both males and females. In both sexes, two different cDNAs were obtained, encoding 123 and 115 amino acid-deduced sequences. Each sequence showed few amino acid differences between the sexes. The proteins were named RpalOBP2 and RpalOBP4 for male, RpalOBP2' and RpalOBP4' for female, with the types 2 and 4 presenting only 34% identities. These proteins shared high identity with previously described coleopteran OBPs. In native gels, RpalOBP2 clearly separated into two bands and RpalOBP4 into three bands, suggesting the presence of several conformational isomers. Thus, OBP diversity in this species may rely on both the presence of OBPs from different classes and the occurrence of isoforms for each OBP.

A new member of the PBAN family in Spodoptera littoralis: molecular cloning and immunovisualisation in scotophase hemolymph

In this article, we report evidence suggesting that the immunoreactive factor previously detected in Spodoptera littoralis scotophase hemolymph is PBAN, which supports a humoral route of the hormone to the pheromone gland. Western blot after native-PAGE of prepurified scotophase hemolymph extracts yielded an immunoreactive band with the same mobility as S. littoralis Br-SOG factor and the expected mobility for a noctuid PBAN. This band was not detected in photophase hemolymph extract. The identity of S. littoralis Br-SOG factor as PBAN was obtained from cDNA cloning using RT-PCR strategy. This allowed us to deduce the amino acid sequence of Spl-PBAN, which is highly homologous to other known PBANs. Moreover, we found that the PBAN encoding cDNA also encoded four other putative amidated peptides (Spl-DH homologue, Spl-alpha-NP, Spl-beta-NP and Spl-gamma-NP) that are identical or highly conserved among noctuids, and two non amidated peptides of unknown function. This cDNA organization is common to all known cDNAs encoding PBANs, leading to the release of different peptides after putative enzymatic cleavage of the preprohormone.

cDNA cloning of biotransformation enzymes belonging to the cytochrome P450 family in the antennae of the noctuid moth Mamestra brassicae

The involvement of cytochrome P450 enzymes in olfaction was demonstrated in vertebrates some time ago. In insects these enzymes are well known for their role in insecticide resistance, but the involvement of P450 in pheromone degradation was only recently demonstrated. Using a PCR strategy, we have isolated two cDNAs from the antennae of the cabbage armyworm Mamestra brassicae - CYP4L4 and CYP4S4 - which encode microsomal P450s. CYP4S4 expression is restricted to the antennae, whereas CYP4L4 is also found in the proboscis and legs. Moreover, the two genes are strongly expressed in one type of sensory unit of the antennae - the sensilla trichodea - which are tuned to the detection of odourants. The putative function of the corresponding enzymes is discussed with regard to their respective expression patterns.

Expression pattern in the antennae of a newly isolated lepidopteran Gq protein alpha subunit cDNA

From the antennae of the moth Mamestra brassicae, we have identified a lepidopteran G protein alpha subunit belonging to the Gq family, through immunological detection in crude antennal extract and antennal primary cell cultures, followed by molecular cloning. The complete cDNA sequence (1540 bp) contains an open reading frame encoding a protein of 353 amino acids. This deduced sequence possesses all of the characteristics of the Gq family and shares a very high degree of amino-acid sequence identity with vertebrate (80% with mouse or human Gqalpha) and invertebrate subunits (varying between 60 and 87% for Gqalpha from organisms as diverse as sponge and Drosophila). The expression pattern of the Gq subunit in adult antennae was associated with the olfactory sensilla suggesting a specific role in olfaction. These data provide molecular evidence for a component of the phosphoinositide signaling pathway in moth antennae: this G protein alpha subunit may be involved in the olfaction transduction process through interaction with G-protein-coupled receptors, stimulating the phospholipase C mediated second messenger pathway.

Functional and expression pattern analysis of chemosensory proteins expressed in antennae and pheromonal gland of Mamestra brassicae

Sequences coding for chemosensory proteins (CSP) CSPMbraA and CSPMbraB, soluble proteins of low mol. wt, have been amplified using polymerase chain reaction on antennal and pheromonal gland complementary DNAs. On the basis of their sequences, these proteins could be classed in the 'OS-D like' protein family whose first member was described in Drosophila, and that includes proteins characterized in chemosensory organs of many insect phylla, including our recent identification in Mamestra brassicae proboscis. Binding assays have shown that these proteins bind the pheromonal component (Z)-11-hexadecenyl-1-acetate (Z11-16:Ac) as well as (Z)-11-octadecenyl-1-acetate (Z11-18:Ac), an other putative component of the M. brassicae pheromonal blend. Furthermore, binding with fatty acids, but not with progesterone that is a structurally unrelated compound, leads to the hypothesis that the odorant-binding capability of the MbraCSPs may be restricted to fatty acids and/or to 16-18 carbon backbone skeletons. Thus, these proteins do not show the same highly binding specificity as the pheromone-binding proteins do. The CSP-related proteins appear homologous based on sequence identity, conserved cysteine residues and general patterns of expression. However, phylogenetic analyses suggest the presence of multiple classes of CSP within a given species and possible diversification of CSPs within different orders. This diversity perhaps contributes to the many CSP functions proposed in the literature. In M. brassicae, we localized the CSPMbraA expression to the sensilla trichodea, devoted to pheromone reception, suggesting a role in the chemosensory pathway. However, we also localized such proteins in the pheromonal gland, devoid of any chemosensory structure. This suggests that the M. brassicae CSP could be involved in transport of hydrophobic molecules through different aqueous media, such as the sensillar lymph, as well as the pheromonal gland cytosol.

Chemosensory proteins from the proboscis of mamestra brassicae

Soluble, low molecular weight proteins were immunodetected in proboscis extracts of Mamestra brassicae males by Western blot, using antibodies raised against the general odorant-binding protein of the moth Antheraea polyphemus. The same antibodies weakly labelled the sensillum lymph and subcuticular space of sensilla styloconica on ultrathin sections of the proboscis. The morphology of sensilla styloconica is described. The immunodetected proteins yielded several N-terminal sequences, three of which showed strong affinity for tritiated analogues of pheromonal compounds of M. brassicae in binding assays. The cDNAs coding for these sequences were cloned and it was shown that the new proteins are related to the OS-D protein of Drosophila. They are named chemosensory proteins (CSP-MBRA:A1-CSP-MBRA:A5 and CSP-MBRA:B1 and CSP-MBRA:B2) and may have an odorant-binding protein-like function. A common localization in both olfaction and taste organs suggests a physiological role depending on the cellular environment.

Molecular cloning of two pheromone binding proteins in the cabbage armyworm Mamestra brassicae

Two cDNA clones encoding pheromone binding proteins (PBPs) were isolated from antennal cDNA of Mamestra brassicae by reverse transcription-polymerase chain reaction (RT-PCR) and rapid amplification of cDNA ends-PCR (RACE-PCR) performed with specific primers deduced from the N-terminal sequences of two PBPs previously reported. The deduced protein sequences of the two PBPs showed a strong relationship between primary structures and functional properties of the corresponding mature proteins.

cDNA cloning and sequence determination of the pheromone biosynthesis activating neuropeptide of Mamestra brassicae: a new member of the PBAN family

Sex pheromone biosynthesis in a number of moth species is induced by a conserved 33-amino acid amidated neuropeptide PBAN (pheromone biosynthesis activating neuropeptide). Here, using immunoblotting and bioassay, we present evidence for the presence of a very similar peptide, called Mab-PBAN, in the brain-subesophageal ganglion complex of Mamestra brassicae females. A partial Mab-PBAN encoding cDNA was isolated using 3'RACE. The deduced amino acid sequence for Mab-PBAN is: LADDMPATPADQEMYRPDPEQIDSRTKYFSPRL with a presumed amidated C-terminus. Mab-PBAN has high homology to the other members of the PBAN peptide family: 94% with Hez-PBAN, 87.9% with Lyd-PBAN and 78.8% with Bom-PBAN. The Mab-PBAN gene encodes, beside Mab-PBAN, at least three putative amidated peptides in the same reading frame, all of them having a common C-terminal pentapeptide motif F(T/S)P(R/K)L-NH2.