Preliminary Binding Characterization of Odorant Binding Protein 2 in the Lucerne Plant Bug, <italic>Adelphocoris lineolatus</italic> (Goeze)

Abstract

Insects can use their sensitive olfactory system to perceive sex pheromones and host volatiles, and trigger specific behavioral reactions, such as detection and location mate partners, host plants and oviposition sites. Odorant binding proteins (OBPs) have been demonstrated to play a crucial role in the olfaction perception in insects. In the present study, a novel OBP protein (AlinOBP2) in the lucerne plant bug, <italic>Adelphocoris lineolatus</italic>, was expressed and purified. The expression intensity of <italic>Alin</italic>OBP2 gene was evaluated by qRT-PCR, which indicated that <italic>Alin</italic>OBP2 was mainly expressed in antennae. The expression level is nearly equivalent between the adult male and female antennae. In addition, <italic>Alin</italic>OBP2 was also expressed in the head with a much lower expression intensity. The binding properties of AlinOBP2 with five sex pheromone analogs and 13 cotton volatiles were measured by fluorescence competitive binding assays with the fluorescence probe N-phenyl-1-naphthylamine (1-NPN). The results reveal that AlinOBP2 cannot effectively bind with the five sex pheromone analogs, indicating AlinOBP2 did not participate in the sex pheromone reception process. Of the 13 cotton volatiles, ethyl heptanoate had the strongest binding affinity with AlinOBP2, with dissociation constant as 9.22 μmol/L. 2-methylnaphthalene, 3-hexanone, cis-3-hexenyl acetate, nonyl acetate, and carveol had medium binding affinities with AlinOBP2, with dissociation constants of 15.49, 17.31, 21.53, 18.86 and 13.47 μmol/L, respectively. The results suggest that AlinOBP2 is a general odorant binding protein (GOBP) and can selectively bind with particular cotton volatiles and participate in the general odorant reception process.