Speaker
Description
Olfactory adaptations play a key role in initiating or stabilizing dietary shifts by reshaping the insect’s responsiveness to host-specific chemical cues. Modulating gene expression or altering the specificity and sensitivity of odorant receptors (ORs) can influence an insect’s ability to recognize host volatiles. However, highlighting these specific molecular changes remains a challenge. Insects can possess hundreds of ORs, most of which are still orphan receptors with unknown ligands. This limited functional characterization constrains current efforts to identify functionally divergent orthologs, which typically rely on sequence similarity alone.
Structure-based virtual screening (SBVS), which employs molecular docking simulations, offers a promising solution to overcome this limitation. While widely used for predicting ligand–receptor interactions in mammalian G protein-coupled receptors (GPCRs), SBVS has only recently been adapted to insect ORs. This strategy allows rapid, repertoire-wide prediction of odorant binding profiles, facilitating cross-species comparisons of olfactory tuning and the identification of functionally divergent receptors associated with ecological specialization.
In this study, we present the first application of SBVS to the entire OR repertoire of an insect, leveraging this approach to explore peripheral olfactory system adaptation associated with host plant shift in the genus Spodoptera. We annotated the full OR repertoire of the oligophagous species S. picta, which feeds exclusively on Amaryllidaceae, and compared its predicted chemical detection space to that of its two polyphagous sister species, S. litura and S. littoralis. We complemented this approach with RNA sequencing to determine the expression profiles of SpicORs. This integrative approach led to the identification of SpicOR29, a receptor highly expressed in S. picta that exhibited distinct sensitivity and selectivity toward volatiles emitted by its Amaryllidaceae hosts (Clivia miniata and Crinum spp.), in contrast to its orthologs in the polyphagous species. Site-directed mutagenesis revealed a single amino acid substitution in SpicOR29 as a key determinant of its shifted ligand sensitivity.
