Recognition Mechanism Of The Peripheral Olfactory On Plant Volatiles In Cotton Bollworm Moth,Helicoverpa Armigera

The chemical sensation of insects plays a key role in almost all the behavioral activities throughout the life cycle.Hence,the use of olfaction to regulate the behavior of pests has been a research hotspot in the research on entomology.Helicoverpa armigera is one of the most damaging pests in China and many other regions all over the world.The high polyphagia and appetite of larvae and the strong migration rate and propagation of adults make the control and management of H.armigera difficult problems.In modern agriculture,where integrated pest management(IPM)is strongly advocated,green prevention and control is especially crucial.Attractants baseded on plant volatiles considered to have great application prospects.The development of attractants in traditional ways need long period and heavy workload.On the contrary,the strategy that targeting olfactory relevant proteins,was thought to be efficient and nichetargeting in screening potential active components.Here,we firstly performed electron microscope scanning on the antenna and mouthparts of adult H.armigera.Then,we conducted transcriptome analysis on labial palps and proboscises,where contain abundant chemosensory genes.Finally,the function of a large number of ORs were identified against plant volatiles.The encoding mechanism of the peripheral olfactory system is described.The research contents and results were listed as follows:1.Ultrastructure of chemosensory organs and Gene location of odorant co-receptor gene in the antenna of Helicoverpa armigeraAs the smallest structure and functional unit of insect chemosensery organs,the receptor is the basic model for studying chemical sesensing.The physiological function of organs in organism is closely related with their morphology,hense,it is of great significance to study the morphological structure of chemosensory organs.Here,systematic studies were performed by conducting electron microscope scanning and In Situ Hybridization to investigate the ultrastructure of antenna and proboscis and the gene location of odorant co-receptor HarmOrco in the antenna.The results indicate that:Six major types were identified on the antenna of adults including sensilla trichodea,sensilla basiconica,sensilla chaetica,sensilla coeloclnica,sensilla auricillica and sensilla styloconica,further 13 sub-types were divided based on their morphological features.For the proboscis,three major types of sensilla including ten sub-types were observed on the proboscis of male and female moths:sensilla sty loconica,sensilla chaetica,and sensilla basiconica.Withnin 23 sub-types of sensilla on the antenna and probosic,9 were reported for the first time.Furthermore,our results indicate that sensilla trichodea sub-type I exists only on the antennae of male moths;One polyporous sensilla(sensilla styloconica II),which were suggested to correlate with odorant sensing,were identified on the proboscis.Finally,Location of HarmOrco on the antenna by In Situ Hybridization showed that HarmOrco mainly express in the sensilla trichodea and sensilla basiconica abundantly.These studies lay the foundation for further research on the functions of receptors.2.Identification of chemosensory genes in the mouthparts accessory organs of mouthparts in Helicoverpa armigeraIn resent years,studies on chemosensory related genes are mainly concentrated on the antennae of insect,however,rarely was focused on mouthpart organs.For further understanding of the chemosensory functions of mouthpart organs,we conducted transcriptome analysis on labial palps and proboscises.The results indicate that:A total of 84 chemosensory genes belonging to six different families were identified in these transcriptomes including 4 ORs,6 IRs,7 GRs,39 OBPs,26 CSPs,and 2 SNMPs,among which 8 OBPs and 6 CSPs were new.The expression level of candidate chemosensory genes in the proboscis and labial palps was evaluated by differentially expressed genes(DEGs)analysis and the expression of candidate chemosensory receptor genes in different tissues was further investigated by quantitative real time PCR(qRT-PCR).All the candidate receptors were detected by DEGs and qRT-PCR,but only a small part of the OR or IR genes specifically or bias expressed in proboscis or labial palps,such as HarmOR58 and HarmIR75p.1,But most of the GRs expressed abundantly in proboscis or labial palps.The reported CO2 receptors HarmGR1,GR2,GR3 mainly expressed in labial palps.HarmGR5,GR6,GR8,which belonging to "sugar receptor" clade,mainly expressed in proboscis or antenna and were therefore suggested to perceiving saccharide.The results suggest the mouthparts are mutually cooperative but functionally concentrated system.These works contribute to the understanding of chemical signal recognition in mouthpart organs and provides the foundation for further functional studies.3.Functional identification and evolutionary analysis of common odorant receptors in Helicoverpa armigeraPlant volatiles play an important role in the life of most insect including:detecting host plants,feeding,recognizing mates,or locating oviposition sites.Hence,systematic research on the function of odorant receptors will greatly help us understand the mechanism of insect identification against plant volatiles,and will have important values on application.Here,sy stematically studies were perfoemed on the mechanism of plant volatiles recognition in H.armigera by sequence cloning,heterologous expression,functional identification and comprehensive analysis of reaction characteristics and functional evolution analysis.The results indicate that:28 among 43 ORs were functional to a wide range of compounds,23 ORs were activated robustly by at least one odorant.Many narrow-tuned ORs,together with a notably broad-tuned OR,had intensive and sensitive responses to significant biological relevant volatiles.The HarmOR repertoire was more sensitive against terpenics or aromatics chemicals than aliphatics.The response properties of ORs were structure-and dosage-depended.Functional evolution analysis of odorant receptors in Lepidoptera insects was carried out.It was suggested that ORs for sensing aromatics might evolved early than that for sensing terpenes and aliphatic compounds,and highly differentiated.Finally,the receptors of the important attractant components of the H.armigera were identified.Furtherly,specific receptors for sensing phenylacetaldehyde and the neuron express the 2 ORs were identified,which revealed the molecular basis for sening phenylacetaldehyde in peripheral olfactory system.This work was suggested to contributing the understanding of the perception to plant volatiles in the Lepidoptera.Further,our results provided general research support to reverse chemical ecology strategy for screening potential attractant components.