Molecular Identification of cDNA, Immunolocalization, and Expression of a Putative Odorant-Binding Protein from an Asian Honey Bee, Apis cerana cerana

An odorant-binding protein cDNA (Acer-ASP2) was cloned and characterized from antennae of adult workers of an Asian honey bee, Apis cerana cerana F. (Hymenoptera: Apidae). The full-length open reading frame of Acer-ASP2 cDNA was 429 bp, encoding 142 amino acids. Protein signature analyses revealed that it contained six conserved cysteines with an N-terminal signal sequence of 19 amino acids. The deduced protein sequence shares high homology with Amel-ASP2 from the honey bee, Apis mellifera L., and low similarity with odorant-binding proteins from other species of insects. Immunocytochemical localization showed that Acer-ASP2 was concentrated in the lymph of olfactory sensilla, such as sensilla placodea and sensilla trichodea A. Real-time polymerase chain reaction of Acer-ASP2 transcripts showed that Acer-ASP2 was expressed on antennae but not in other general anatomical regions of the body. Temporally, Acer-ASP2 was expressed at a relatively high level in adults during two periods (9 and 27 vs. 1, 15, and 30 days). This timing is correlated with the production of beeswax and searching behavior for nectar/pollen, respectively. Thus, Acer-ASP2 is a species-specific gene that we propose to be involved in the acquisition of odorant molecules from nectar, pollen, and other general odorant sources.