Ionotropic Receptors (IRs): Chemosensory ionotropic glutamate receptors in Drosophila and beyond

Ionotropic Receptors (IRs) are a recently characterized family of olfactory receptors in the fruit fly, Drosophila melanogaster. IRs are not related to insect Odorant Receptors (ORs), but rather have evolved from ionotropic glutamate receptors (iGluRs), a conserved family of synaptic ligand-gated ion channels. Here, we review the expression and function of IRs in Drosophila, highlighting similarities and differences with iGluRs. We also briefly describe the organization of the neuronal circuits in which IRs function, comparing and contrasting them with the sensory pathways expressing ORs. Finally, we summarize the bioinformatic identification and initial characterization of IRs in other species, which imply an evolutionarily conserved role for these receptors in chemosensation in insects and other protostomes.     

Cloning and expression profile of ionotropic receptors in the parasitoid wasp Microplitis mediator (Hymenoptera: Braconidae)

Ionotropic receptors (IRs) mainly detect the acids and amines having great importance in many insect species, representing an ancient olfactory receptor family in insects. In the present work, we performed RNAseq of Microplitis mediator antennae and identified seventeen IRs. Full-length MmedIRs were cloned and sequenced. Phylogenetic analysis of the Hymenoptera IRs revealed that ten MmedIR genes encoded “antennal IRs” and seven encoded “divergent IRs”. Among the IR25a orthologous groups, two genes, MmedIR25a.1 and MmedIR25a.2, were found in M. mediator. Gene structure analysis of MmedIR25a revealed a tandem duplication of IR25a in M. mediator. The tissue distribution and development specific expression of the MmedIR genes suggested that these genes showed a broad expression profile. Quantitative gene expression analysis showed that most of the genes are highly enriched in adult antennae, indicating the candidate chemosensory function of this family in parasitic wasps. Using immunocytochemistry, we confirmed that one co-receptor, MmedIR8a, was expressed in the olfactory sensory neurons. Our data will supply fundamental information for functional analysis of the IRs in parasitoid wasp chemoreception.     

稻纵卷叶螟绒茧蜂对寄主的搜索行为

稻纵卷叶螟绒茧蜂是稻纵卷叶螟幼虫的重要天敌。以Y形嗅觉仪测定了稻纵卷叶螟2—3龄幼虫虫粪、4—5龄幼虫虫粪、健康水稻、稻纵卷叶螟幼虫为害后水稻在纵卷叶螟绒茧蜂对寄主的搜索过程中的作用。结果表明已交配的雌蜂显著趋向稻纵卷叶螟2—3龄幼虫虫粪和4—5龄幼虫虫粪,不趋向健康水稻、稻纵卷叶螟幼虫为害后的水稻。雄蜂、处女雌蜂不显著趋向健康水稻、稻纵卷叶螟幼虫为害后水稻、稻纵卷叶螟2—3龄幼虫虫粪、稻纵卷叶螟4—5龄幼虫虫粪。利用固相微萃取(SPME)及气相色谱/质谱(GC/MS)联用分析稻纵卷叶螟2—3龄幼虫虫粪的化学成分,并通过Y-形嗅觉仪测试已交配雌蜂对稻纵卷叶螟2—3龄幼虫虫粪化学成分标准品的嗅觉反应,结果表明已交配的雌蜂显著趋向1-十一烯和异缬草醛,稻纵卷叶螟幼虫虫粪中的1-十一烯和异缬草醛可能是稻纵卷叶螟绒茧蜂搜索寄主的利他素。