Identification of novel odorant binding protein genes and functional characterization of OBP8 in Chilo suppressalis...

At the peripheral level of the insect olfaction, odorant binding proteins (OBPs) are thought to bind and transport exogenous hydrophobic volatiles to the odorant receptors (ORs) located on the dendrite membrane of the olfactory neurons. In this study, cDNA sequences of 29 OBP genes from Chilo suppressalis, a notorious rice pest, were identified, with 15 of them being newly reported. The tissue and temporal expression patterns of these CsupOBPs were determined by RT-PCR, revealing that CsupOBP8, 10 and 24 were specifically expressed in the heads at larval stage and in antennae of both sexes at adult stage. In addition, CsupOBP 6, 9 and 18 were expressed in much higher levels in heads than abdomen at the larval stage, while CsupPBP4 and CsupOBP1, 3, 8, 11 and 24 were specifically expressed in antennae of both sexes at the adult stage. Such expression profile strongly suggests olfactory roles of these genes. Furthermore, the function of CsupOBP8 was chosen to be investigated by the competitive fluorescence binding assay. Results showed that CsupOBP8 displayed high binding affinities (Ki=4.9-15.0μM) with plant volatile β-ionone, nerolidol, farnesol and 2-hexanone, suggesting that CsupOBP8 plays olfactory roles through binding and transporting the plant volatiles. The study provides an important base for understanding the olfactory mechanisms in C. suppressalis.