Functional Analysis of Odorant-Binding Proteins 12 and 17 from Wheat Blossom Midge Sitodiplosis mosellana Géhin (Diptera: Cecidomyiidae)

SIMPLE SUMMARY: Sitodiplosis mosellana is one of the most destructive pests of wheat. Adults rely highly on wheat spike volatiles to search and locate oviposition sites. Insect odorant-binding proteins (OBPs) are important in binding and transporting host plant volatiles to the olfactory receptors. Therefore, OBP-based behavioral interference is believed to be a novel and effective pest management strategy. The objectives of this study were to clone two S. mosellana female antenna-enriched OBP genes (SmosOBP12 and SmosOBP17), determine the functions of the encoded SmosOBP proteins in binding wheat volatiles, and investigate behavioral responses of female S. mosellana to odorant molecules. Results indicated that SmosOBP12 had a broader ligand-binding spectrum than SmosOBP17 to wheat volatiles. Female S. mosellana showed intensive response to 3-hexanol, 1-octen-3-ol, D-panthenol, 3-carene, (Z)-3-hexenylacetate, hexyl acetate, methyl salicylate, heptyl acetate, ethyl heptanoate, α-farnesene, and ocimene. Notably, all these compounds except α-farnesene exhibited strong affinity to SmosOBP12. In conclusion, SmosOBP12 may play more crucial roles than SmosOBP17 in perception and transportation of biologically active host volatiles. This information has enhanced our molecular understanding of the S. mosellana olfaction, which could also serve as an important reference for developing attractants or repellents to control this pest. ABSTRACT: The wheat blossom midge Sitodiplosis mosellana, one of the most disastrous wheat pests, depends highly on olfactory cues to track suitable plants. To better understand the olfactory recognition mechanisms involved in host selection, in the present study we cloned two S. mosellana adult antenna-specific odorant binding protein (OBP) genes, SmosOBP12 and SmosOBP17, and evaluated bacterially expressed recombinant proteins for their selectivity and sensitivity for host wheat volatiles using the fluorescence-based ligand binding assay. The results showed that both SmosOBPs effectively bound alcohol, ester, ketone, and terpenoid compounds. Particularly, SmosOBP12 had significantly higher affinities (K(i) < 10.5 μM) than SmosOBP17 (K(i)2 > 0.1 μM) to 3-hexanol, 1-octen-3-ol, D-panthenol, 3-carene, (Z)-3-hexenylacetate, hexyl acetate, methyl salicylate, heptyl acetate, and ethyl heptanoate. Consistently, S. mosellana females were attracted to all these chemicals in a behavioral assay using Y-tube olfactometer. SmosOBP12 also bound aldehyde, but neither bound alkanes. Notably, SmosOBP12 exhibited strong affinity to ocimene (K(i) = 8.2 μM) that repelled S. mosellana. SmosOBP17, however, was insensitive to this compound. Taken together, our results indicate that SmosOBP12 may play a greater role than SmosOBP17 in perceiving these biologically active plant volatiles.