Study of the obp5 gene in Apis mellifera ligustica and Apis cerana cerana

Apis mellifera ligustica and A. cerana cerana exhibit differences in olfactory sensitivity to odors from nectariferous plants and diseased broods. It is presumed that the differences in odorant-binding proteins (OBPs) between these 2 species contribute to their olfactory sensitivity. We compared the sequences, temporal expression pattern, and binding properties of the 2 OBP-encoding genes. We cloned the Amobp5 and Acobp5 genes. Among the ligands tested, phenethyl acetate was the most variable, with AcOBP5 showing high affinity and AmOBP5 having no apparent affinity for this ligand. While AmOBP5 had high affinity to both benzyl alcohol and 2-phenylethanol, the binding affinity of AcOBP5 to these compounds was moderate. However, the fluorescence intensity of these compounds was not decreased below 50%; thus, the dissociation constants could not be calculated. The Amobp5 gene showed significantly higher expression in 10- and 15-day-old workers than in other stages, while the Acobp5 gene had the highest expression in 30-day-old workers. Both the Amobp5 and Acobp5 genes had the lowest expression level in 1-day-old workers. These results suggest that the binding properties and temporal expression patterns of the obp5 genes in A. mellifera and A. cerana play a critical role in the olfactory sensitivity of workers.