Two general odorant binding proteins display high bindings to both host plant volatiles and sex pheromones in a pyralid moth Chilo suppressalis (Lepidoptera: Pyralidae)

Abstract

Odorant sensitivity and selectivity play a crucial role in insects for finding host plants, mates and oviposition sites. General odorant binding proteins (GOBPs) are thought to be involved in the detection of general odorants released by foods and host plants. However, recent studies suggest GOBPs may also play some role in detection of sex pheromones. In the present study with the rice striped stem borer Chilo suppressalis (Walker) real time quantitative PCR (qPCR) measurements showed that both GOBP genes were specifically expressed in the antennae of both sexes, proposing their important roles in olfaction. To examine their specific functions, binding affinities to three sex pheromones and 35 plant volatiles were measured using fluorescence competitive binding assays. As a result, both GOBPs showed very strong binding affinities (Ki=0.33–1.50μM) to all three sex pheromone components (Z11–16:Ald, Z9–16:Ald and Z13–18:Ald). In addition, GOBP1 and GOBP2 displayed high binding affinities (Ki<10μM) to two volatiles (farnesol and oleic acid) and five volatiles (+)-cedrol, farnesol, myrcene, β-ionone and linoleic acid), respectively; GOBP1 and GOBP2 also displayed moderate binding affinities (Ki=10–20μM) to two and one compounds, respectively. Furthermore, electroantennogram (EAG) measurements indicated that except oleic acid and myrcene, all volatiles of high binding affinity could elicit significant EAG response in moths of one or both sexes. Our study suggests that two CsupGOBPs tune to different array of plant volatiles, and also play roles in perception of the female sex pheromones, providing insights in to the mechanisms of olfaction in C. suppressalis.