Function and immunocytochemical localization of two novel odorant-binding proteins in olfactory sensilla of the scarab beetle Holotrichia oblita Faldermann (Coleoptera: Scarabaeidae)

Odorant-binding proteins (OBPs) are found in both insects and vertebrates, and it is believed that they are involved in chemical communication. In this study, we identify and express 2 OBPs from the scarab beetle, Holotrichia oblita Faldermann (Coleoptera: Scarabaeidae). HoblOBP1 shows more similarities with other scarab beetle OBPs, whereas HoblOBP2 is more diverse. N-phenyl-1-naphthylamine (1-NPN) is used as a fluorescent probe in ligand-binding experiment, and results indicate that both HoblOBPs prefer plant volatiles to putative H. oblita sex pheromones. HoblOBP1 shows binding affinity to a wider range of test compounds, but HoblOBP2 displays more specific binding affinity. Cinnamaldehyde and 2,4-di-tert-butylphenol bind to HoblOBP1 can elicit strong electrophysiological responses of the antennae from female H. oblita adults, respectively. Methyl salicylate also shows good affinity to HoblOBP2 and it can elicit moderate electrophysiological responses. Although, β-ionone is one of the ligands of the strongest binding, it elicits a weak electrophysiological response. In the immunocytochemical analysis, we observe that HoblOBP1 and HoblOBP2 are coexpressed in sensilla basiconica and placodea in both sexes.