Sex-Biased Expression of Olfaction-Related Genes in the Antennae of <i>Apis cerana</i> (Hymenoptera: Apidae).

The olfactory system is essential for honeybees to adapt to complex and ever-changing environments and maintain cohesiveness. The Eastern honeybee <i>Apis cerana</i> is native to Asia and has a long history of managed beekeeping in China. In this study, we analysed the antennal transcriptomes of <i>A. cerana</i> workers and drones using Illumina sequencing. A total of 5262 differentially expressed genes (DEGs) (fold change &amp;gt; 2) were identified between these two castes, with 2359 upregulated and 2903 downregulated in drones compared with workers. We identified 242 candidate olfaction-related genes, including 15 odourant-binding proteins (OBPs), 5 chemosensory proteins (CSPs), 110 odourant receptors (ORs), 9 gustatory receptors (GRs), 8 ionotropic receptors (IRs), 2 sensory neuron membrane proteins (SNMPs) and 93 putative odourant-degrading enzymes (ODEs). More olfaction-related genes have worker-biased expression than drone-biased expression, with 26 genes being highly expressed in workers' antennae and only 8 genes being highly expressed in drones' antennae (FPKM &amp;gt; 30). Using real-time quantitative PCR (RT-qPCR), we verified the reliability of differential genes inferred by transcriptomics and compared the expression profiles of 6 ORs (<i>AcOR10</i>, <i>AcOR11</i>, <i>AcOR13</i>, <i>AcOR18</i>, <i>AcOR79</i> and <i>AcOR170</i>) between workers and drones. These ORs were expressed at significantly higher levels in the antennae than in other tissues (<i>p</i> &amp;lt; 0.01). There were clear variations in the expression levels of all 6 ORs between differently aged workers and drones. The relative expression levels of <i>AcOR10</i>, <i>AcOR11</i>, <i>AcOR13</i>, <i>AcOR18</i> and <i>AcOR79</i> reached a high peak in 15-day-old drones. These results will contribute to future research on the olfaction mechanism of <i>A. cerana</i> and will help to better reveal the odourant reception variations between different biological castes of honeybees.