Transcriptome sequencing reveals abundant olfactory genes in the antennae of the rice leaffolder,Cnaphalocrocis medinalis(Lepidoptera: Pyralidae)

The rice leaffolder, Cnaphalocrocis medinalis Guenee, is an important lepidopteran pest of rice in Asia. Insect olfactory proteins, including olfactory receptors (ORs), ionotropic receptors (IRs), odorant-binding proteins (OBPs), chemosensory proteins (CSPs) and sensory neuron membrane proteins (SNMPs), are responsible for perception of sex pheromones and host plant volatiles, and thus regulate insect behavior. In the present study, transcriptome sequencing was conducted for C. medinalis antennae to identify genes involved in olfaction. A total of 45800 unigenes were assembled from the transcriptome dataset. Of these, 19696 (43.0%) unigenes were annotated by searching against the NCBI non-redundant database. Functional classification of these unigenes were also conducted by using the Gene Ontology (GO) and Cluster of Orthologous Groups (COG) databases. We identified 90 putative olfactory genes (including 37 novel ones): 46 ORs, 15 IRs, 12 OBPs, 15 CSPs and two SNMPs. BLASTX best hit results indicated that these genes were most identical to their respective orthologs from other lepidopteran insects. Quantitative reverse transcription-PCR (qRT-PCR) assays were performed to investigate the expression profiles of newly identified OR genes. All of the OR genes were antennae-specific or antennae-enriched. Of these, CmedOR28 and CmedOR31 were mainly expressed in male antennae, while CmedOR27 and CmedOR32 were enriched in female antennae. Our results establish a solid foundation for future functional studies of these genes.