A conserved odorant receptor identified from antennal transcriptome of Megoura crassicauda that specifically responds to cis-jasmone

Herbivore-induced plant volatiles(HIPVs)play a key role in the interactions between plants and herbivorous insects,as HIPVs can promote or deter herbivorous insects’behavior.While aphids are common and serious phloem-feeding pests in farmland ecosystems,little is known about how aphids use their sensitive olfactory system to detect HIPVs.In this study,the antennal transcriptomes of the aphid species Megoura crassicauda were sequenced,and expression level analyses of M.crassicauda odorant receptors(ORs)were carried out.To investigate the chemoreception mechanisms that M.crassicauda uses to detect HIPVs,we performed in vitro functional studies of the ORs using 11 HIPVs reported to be released by aphid-infested plants.In total,54 candidate chemosensory genes were identified,among which 20 genes were ORs.McraOR20 and McraOR43 were selected for further functional characterization because their homologs in aphids were quite conserved and their expression levels in antennae of M.crassicauda were relatively high.The results showed that McraOR20 specifically detected cis-jasmone,as did its ortholog ApisOR20 from the pea aphid Acyrthosiphon pisum,while McraOR43 did not respond to any of the HIPV chemicals that were tested.This study characterized the ability of the homologous OR20 receptors in the two aphid species to detect HIPV cis-jasmone,and provides a candidate olfactory target for mediating aphid behaviors.

Odorant receptor orthologues from moths display conserved responses to cis-jasmone

In insects,the odorant receptor(OR)multigene family evolves by the birth-and-death evolutionary model,according to which the OR repertoire of each species has undergone specific gene gains and losses depending on their chemical environment,resulting in taxon-specific OR lineage radiations with different sizes in the phylogenetic trees.Despite the general divergence in the gene family across different insect orders,the ORs in moths seem to be genetically conserved across species,clustered into 23 major clades containing multiple orthologous groups with single-copy gene from each species.We hypothesized that ORs in these orthologous groups are tuned to ecologically important compounds and functionally conserved.cis-Jasmone is one of the compounds that not only primes the plant defense of neighboring receiver plants,but also functions as a behavior regulator to various insects.To test our hypothesis,using Xenopus oocyte recordings,we functionally assayed the orthologues of BmorOR56,which has been characterized as a specific receptor for cis-jasmone.Our results showed highly conserved response specificity of the BmorOR56 orthologues,with all receptors within this group exclusively responding to cis-jasmone.This is supported by the dN/dS analysis,showing that strong purifying selection is acting on this group.Moreover,molecular docking showed that the ligand binding pockets of BmorOR56 orthologues to cis-jasmone are similar.Taken together,our results suggest the high conservation of OR for ecologically important compounds across Heterocera.