BACKGROUND: Bark beetles are major pests of conifer forests, and their behavior is primarily mediated via olfaction. Targeting the odorant receptors (ORs) may thus provide avenues towards improved pest control. Such an approach requires information on the function of ORs and their interactions with ligands, which is also essential for understanding the functional evolution of these receptors. Hence, we aimed to identify a high-quality complement of ORs from the destructive spruce bark beetle Ips typographus (Coleoptera, Curculionidae, Scolytinae) and analyze their antennal expression and phylogenetic relationships with ORs from other beetles. Using 68 biologically relevant test compounds, we next aimed to functionally characterize ecologically important ORs, using two systems for heterologous expression. Our final aim was to gain insight into the ligand-OR interaction of the functionally characterized ORs, using a combination of computational and experimental methods. RESULTS: We annotated 73 ORs from an antennal transcriptome of I. typographus and report the functional characterization of two ORs (ItypOR46 and ItypOR49), which are responsive to single enantiomers of the common bark beetle pheromone compounds ipsenol and ipsdienol, respectively. Their responses and antennal expression correlate with the specificities, localizations, and/or abundances of olfactory sensory neurons detecting these enantiomers. We use homology modeling and molecular docking to predict their binding sites. Our models reveal a likely binding cleft lined with residues that previously have been shown to affect the responses of insect ORs. Within this cleft, the active ligands are predicted to specifically interact with residues Tyr84 and Thr205 in ItypOR46. The suggested importance of these residues in the activation by ipsenol is experimentally supported through site-directed mutagenesis and functional testing, and hydrogen bonding appears key in pheromone binding. CONCLUSIONS: The emerging insight into ligand binding in the two characterized ItypORs has a general importance for our understanding of the molecular and functional evolution of the insect OR gene family. Due to the ecological importance of the characterized receptors and widespread use of ipsenol and ipsdienol in bark beetle chemical communication, these ORs should be evaluated for their potential use in pest control and biosensors to detect bark beetle infestations.
An animal's fitness strongly depends on successful feeding, avoidance of predators and reproduction. All of these behaviours commonly involve chemosensation. As a consequence, when species' ecological niches and life histories differ, their chemosensory abilities need to be adapted accordingly. The intertidal insect Clunio marinus (Diptera: Chironomidae) has tuned its olfactory system to two highly divergent niches. The long-lived larvae forage in a marine environment. During the few hours of terrestrial adult life, males have to find the female pupae floating on the water surface, free the cryptic females from their pupal skin, copulate and carry the females to the oviposition sites. In order to explore the possibility for divergent olfactory adaptations within the same species, we investigated the chemosensory system of C. marinus larvae, adult males and adult females at the morphological and molecular level. The larvae have a well-developed olfactory system, but olfactory gene expression only partially overlaps with that of adults, likely reflecting their marine vs. terrestrial lifestyles. The olfactory system of the short-lived adults is simple, displaying no glomeruli in the antennal lobes. There is strong sexual dimorphism, the female olfactory system being particularly reduced in terms of number of antennal annuli and sensilla, olfactory brain centre size and gene expression. We found hints for a pheromone detection system in males, including large trichoid sensilla and expression of specific olfactory receptors and odorant binding proteins. Taken together, this makes C. marinus an excellent model to study within-species evolution and adaptation of chemosensory systems.
- MeSH
- biologická adaptace fyziologie MeSH
- bulbus olfactorius metabolismus fyziologie MeSH
- Chironomidae metabolismus fyziologie MeSH
- čich fyziologie MeSH
- čichové buňky metabolismus MeSH
- hmyz metabolismus fyziologie MeSH
- hmyzí proteiny metabolismus MeSH
- kladení vajíček fyziologie MeSH
- kukla metabolismus fyziologie MeSH
- larva metabolismus MeSH
- pohlavní dimorfismus * MeSH
- receptory pachové metabolismus MeSH
- sensilla metabolismus fyziologie MeSH
- vodní organismy metabolismus fyziologie MeSH
- zvířata MeSH
- Check Tag
- mužské pohlaví MeSH
- ženské pohlaví MeSH
- zvířata MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
