Identification of candidate olfactory genes in cicada Subpsaltria yangi by antennal transcriptome analysis.

Olfaction in antennae is essential for regulating insect behaviors such as host preference and oviposition site selection. To better understand the olfactory mechanisms in the cicada Subpsaltria yangi that has a very narrow host range far fewer than diets of most other cicadas, an antennal transcriptome was constructed in this study. We identified 10 unigenes encoding putative odorant-binding proteins (OBPs), 10 chemosensory proteins (CSPs), 8 sensory neuron membrane proteins (SNMPs), 7 gustatory receptors (GRs), 29 odorant receptors (ORs) and 13 ionotropic receptors (IRs). We found that the OBPs were separated into two groups, Classic OBPs and Plus-C OBPs, according to their motifs. Based on sequence alignment and phylogenetic analysis, we found five Orcos in OR family. However, no pheromone receptor was identified, which may be related to that cicadas are sound-producing insects and acoustic signals other than pheromones play most important role in sexual communication. We used qRT-PCR to examine the expression profile of ten OBPs genes in various organs, and found that they were mainly expressed in olfactory organs such as antennae and mouthparts. Our results make it possible for future research of the olfactory system of S. yangi at the molecular level, and provide important bases for elucidation of the molecular mechanisms and evolution of chemosensation in sap-sucking insects.