| Sitotroga cerealella is one of the main grain storage pests,which can occur in most provinces in China and cause serious damage to wheat and corn during storage.The olfactory system plays an important role in various life activities of insects such as foraging,courtship,and host search for ovipositing.Odorant binding proteins in the hemolymph play a key role in the olfactory system and are involved in the odor molecule perception,discrimination and transshipment.In order to gain a systematic and in-depth understanding of the olfactory system and explore the role of several odor-binding proteins in host selection of S.cerealella,we analyzed the antennae transcriptome data of S.cerealella,and identified a large number of olfactory genes.Then,headspace solid-phase microextraction and gas chromatography-mass spectrometry were used to identify odors in wheat samples.After,molecular docking was used to analyze the binding ability and binding sites between the odor molecules and the odorant binding proteins with high expression level in the antennae of S.cerealella.Besides,Y-type olfactory and Electroantennography were used to analyze the selective behavior and response values of S.cerealella to different volatiles.The results provide support for further research on the olfactory system of S.cerealella.and can help to reveal the mechanism of odor-binding protein in host recognition of S.cerealella.Besides the results lay a foundation for the development of novel control agents and control strategies based on olfactory system.The main results are as follows:(1)In this study,167 candidate olfactory genes were identified by high-throughput transcriptome sequencing technology with non-reference of the antennae transcriptome of S.cerealella,including 33 Odorant binding proteins,10 Chemosensory proteins,58 Odorant receptors,41 Ionotroic receptors,21 Gustatory receptors,2 Sensory neuron membrane proteins,and 2 Odorant degrading enzymes.(2)Headspace solid-phase microextraction and gas chromatography-mass spectrometry were used to analyze odors in wheat samples of different treatments.A total of 27 volatile compounds were identified from intact wheat,broken wheat and wheat eaten by S.cerealella,including 6 compounds,such as alkanes,ketones,acids,esters,aldehydes and alcohols.There were 19 volatile compounds in intact wheat,among which 4,6-dimethyl-dodecane was the highest content of 24.81%.There were 18 volatile compounds in crushed wheat,among which 4,6-dimethyldodecane was the highest content of 31.16%.A total of 15 volatile compounds were identified in wheat fed by S.cerealella,among which palmitic acid was the highest content of 43.70%,and 6 new compounds were produced in wheat fed by S.cerealella.(3)Based on FPKM values,we selected three odorant binding proteins(Scer GOBP2,Scer OBP15 and Scer OBP23),which are heavily expressed in antennae of S.cerealella,for homologous modeling and molecular docking.The results showed that the three odorant binding protein models were of good quality.Molecular docking showed that n-heptadecane had the strongest binding ability to Scer OBP23,and it is located in the hydrophobic binding cavity composed by 6 α-helices of Scer OBP23.The hydrophobic forces between them maintain the stability of the protein-ligand complex structure.Scer GOBP2 is also most strongly bound to 2,10-Dimethyl-5,9-undecadien-2-and is linked by hydrophobic forces and hydrogen bond.Scer OBP15 has the strongest binding capacity with2,10-Dimethyl-5,9-undecadien-2-and they are connected by hydrophobic forces.(4)Electroantennography technique and Y-type olfactometer were used to analyze the response value and selection behavior of S.cerealella to 12 wheat volatiles(100 mg/ml).The results showed that nonaldehyde elicited the significantly stronger responses in mated and unmated male S.cerealella to than those to other volatiles(P<0.05).The mated and unmated female S.cerealella have higher EAG reaction values to decanal,nonanal and methyl heptenone.The behavioral response results of the Y-type olfactometer showed that palmitic acid had a better attraction effect on both male and female wheat moths,while decanal,nonanal,and iododecane had a certain repellent activity on both male and female wheat moths before and after mating. |
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