Identification of complete repertoire of apis florea odorant receptors reveals complex orthologous relationships with apis mellifera

Abstract

Wedevelopedacomputationalpipeline forhomologybased identificationof thecomplete repertoireofolfactory receptor (OR)genes in theAsian honey bee species, Apis florea. Apis florea is phylogenetically themost basal honey bee species and also themost distant sister species to the Western honey bee Apis mellifera, for which all OR genes had been identified before. Using our pipeline, we identified180ORgenes inA.florea,which is very similar tothenumberofORsidentified inA. mellifera (177ORs).Manycharacteristics of the ORs including gene structure, synteny of tandemly repeated ORs and basic phylogenetic clustering are highly conserved. The composite phylogenetic tree of A. florea and A. melliferaORs could be divided into 21 clades which are in harmony with the existing Hymenopteran tree. However, we found a few nonorthologous OR relationships between both species as well as independent pseudogenization ofORs suggestingseparate evolutionary changes. Particularly, a subgroup of theORgenecladeXI, whichhadbeen hypothesized to code cuticular hydrocarbon receptors showed a high number of species-specific ORs. RNAseq analysis detected a total number of 145 OR transcripts in male and 162 in female antennae. Most of the OR geneswere highly expressed on the female antennae. However, we detected five distinct male-biased OR genes, out of which three genes (AfOr11, AfOr18, AfOr170P) were shown to be male-biased in A. mellifera, too, thus corroborating a behavioral function in sex-pheromone communication.