Molecular Chemoreception Mechanisms For Recognition Of Two Aldehydes And One Ester In Insects

As the largest animal population on the earth,insect evolved complicated chemosensory systems to sense the ambient environment and adapt themselves.Olfactory and gustatory systems facilitate insects distinct and exploit surrounding chemicals(volatile and non-volatile)to direct their behaviors,such as food selection and oviposition site choice.Olfactory Receptors in insect consist of two separate families:odorant receptors and inotropic receptors,among which have divided sensory spectrum representing different ecological significances,however,whether these two receptor populations interact mutually remains unknown.Generally,single member in Gustatory Receptors has narrow tunings,which targets certain chemical category,such as sugar and bitter substances.However,it requires more investigations to identify innovative ligands.Large number of species in Orthoptera and Diptera are treated as pests in agriculture and sanitation and therefore,it's critically significant to explore the mechanisms underlying their olfactory and gustatory behaviors.As common pest on the grassland and farmland,migratory locust,Locusta migratoria has enormous food consumption,which causes predominant agricultural loss,however,the molecular basis underlying food selection remains unclear,especially for molecular recognition toward food source in short range.The larva of fruit fly,Drosophila melanogaster has small size and is unable to migrate from consumed food patch to new one in long distance,which drives the parental females choose the optimum site before egg-laying.Though females probe abiotic tastes related with oviposition via highly evolved gustatory system,how much influence of intraspecies communications on successful egg-laying site choice,as well as sensory mechanisms are rarely explored.This thesis reported how locust mouthpart palps respond to food volatiles in a view of molecular biology and behavior and identified two different olfactory molecular pathways underlying the functional recognition of two volatile aldehydes.On the another hand,we discussed how larval chemicals affect gravid females on egg-laying site choice and identified one fatty acid ester as active compound in female oviposition site preference,as well as its gustatory receptor,which broadens ligand spectrum of bitter gustatory receptor.The key research results are listed below:?.Identification and functional exploration of two olfactory pathways for aldehydes detection on locust mouthpartThis work reported the olfactory molecular mechanisms underlying how locust mouthpart palps detect food cues in short range and identified two olfactory pathways in conjunction of molecular biology and behavioral assays.Firstly,we characterized the distinct roles between antennae and mouthpart palps in long-distance olfactory recognition to food cues via modified olfactometer and found that it's antennae,not palps contributing to long-range navigation,while higher dosage volatile elicited emesis of antennae-ablated locusts in shortened distance.Next,we developed an easy-to-use behavioral paradigm called Palp Opening Response(POR)and it demonstrated that palps enable to recognize certain odors specifically and sensitively,such as multiple aldehydes categorized as green leaf volatiles.Molecular experiment supported that odorant receptor co-receptor LmigOrco,tuning odorant receptor LmigOR2 and odorant-binding protein Lmigobpl are associated from the same olfactory sensilla Basiconica on the mouthpart palps,constituting a complete olfactory pathway.RNA interference(RNAi)allowed specific expression regulation of olfactory genes in a systematical way and the following disruption of LmigOrco,LmigOR2 and Lmigobpl caused severe POR defects when tested against E-2-Hexenal and Hexanal.Besides,sensory neurons expressing ionotropic receptor co-receptor LmigIR8a and odorant-binding protein Lmigobp2a were found co-localized in the same terminal sensilla Chaetica on the palps and similarly,RNAi resulted in successful down-regulation of their normal expression and in subsequent deficient POR response to Hexanal exclusively.Finally,double RNAi against LmigOrco and LmigIR8a led to absolute removal of POR activity to Hexanal.Thus,both odorant receptors and ionotropic receptors contributed to POR response to Hexanal on the locust mouthpart.?.Identification and functional exploration of gustatory pathways for larval ester recognition related with Drosophila females egg-laying site choiceWe discussed how larval chemicals influenced intraspecies gravid females toward egg-laying site choice and identified taste compounds and related gustatory receptor involved.First of all,in total 12 compounds extracted with soaking larvae were characterized via GC-MS and this chemical mixture stimulated gravid females to lay eggs preferentially,which was independent with Orco-pathway.Egg-laying assays with single larval compound and also adult sexual chemicals indicated that only one fatty acid ester,(Z)-9-Octadecenoic acid ethyl ester(OE)evoked similar behavioral activity like larval compounds mixture.OE functioned in manner of dose-dependence and this process was independent of substrate chemical constitution.In addition,the existence of OE significantly accelerated female egg-laying.Mutation of poxn blocked peripheral taste sensory system and resulted in the loss of egg-laying preference to both larval compounds and OE;partial and full genetic rescues of poxn mutant restored female egg-laying preference to both larval compounds and OE.Further evidence proved it was tarsal taste sensilla,not labellum taste bristles sensing OE.Screens of taste receptor loss-of-function mutants and subsequent transgenic rescue identified Gr32a as the candidate target responsible for egg-laying site choice.These results broaden our understanding of the molecular basis underlying herbivores food searching and oviposition site selection behavior and also provide new molecular targets for innovative pest management strategies in the future.