Tissue distribution and functional characterization of odorant binding proteins in Chilo suppressalis (Lepidoptera: Pyralidae)

Abstract

Odorant binding proteins (OBPs) play important roles in the insect olfaction and other diverse physiological processes. Forty OBP genes have been molecularly identified from Chilo suppressalis (Walker), a notorious rice pest in Asian countries, but little is known about the olfactory function for most of these genes. In the present study, we first determined the tissue expression profiles of 34 OBPs (excluding two general odorant bonding proteins (GOBPs) and four pheromone binding protein (PBPs)) by quantitative real-time PCR (qPCR), and found that 9 genes (OBP1, 3, 4, 11, 15, 17, 19, 20 and 24) were specifically or predominantly expressed in antennae of both sexes, suggesting their roles in olfaction, while three genes (OBP29, 30 and 32) were almost not expressed in antennae. Focusing on olfactory roles, the ligand specificities of six antenna specifically or predominantly expressed genes were further investigated for 35 plant volatiles, using the fluorescence competitive binding assays. The results revealed that six OBPs displayed different ligand preference, suggesting a differentiation of OBPs in ligand binding spectrum. Of six tested OBPs, OBP3, 11, 17, 19 and 31 showed moderate (Ki=10.21–19.85μM) or high (Ki<10.00μM) binding affinity for 11 and one plant volatiles, respectively. In particular, a plant volatile β-ionone had high or moderate binding to all five OBPs. Our study suggests that these five OBP genes play important roles in the perception of different host plant volatiles, providing insight into the olfactory mechanism in C. suppressalis.