Identification of candidate chemosensory receptors based on transcriptome analysis in the monophagous insect Protegira songi (Lepidoptera, Noctuidae)

Insects perceive chemical cues from conspecifics and hosts through their sensitive chemosensory system. The chemosensory receptors, which are mainly represented by odorant receptors (ORs), ionotropic receptors (IRs), and gustatory receptors (GRs), are highly enriched in the chemosensory tissues and are crucial for perceiving and transducing chemical signals. In this study, we performed a transcriptome analysis of different tissues of Protegira songi, a notorious defoliator that specifically infests the medicinal and rubber plant Eucommia ulmoides and identified 77 candidate chemosensory receptors (50 PsonORs, 19 PsonIRs, and 8 PsonGRs). Gene expression were analyzed based on the transcriptome data. Sample relationship analysis revealed that the gene expression profiles of male and female antennae were highly correlated and formed an independent group from other tissues. Furthermore, the gene expression patterns of the antennae also showed a high degree of correlation with those of the mouthparts. PsonORs, PsonIRs, and PsonGRs are all transmembrane proteins. They exhibit high sequence divergence within their respective families, yet share high sequence identity with their orthologues in other Lepidoptera insects. Most PsonORs and PsonIRs are primarily expressed in male and female antennae, whereas mouthparts are the main sites for PsonGRs expression. Our results suggest that the antennae and mouthparts are critical chemosensory organs in P. songi. PsonORs, PsonIRs, and PsonGRs exhibit typical sequence features of insect chemosensory receptors, and those highly enriched in these organs may play an important role in chemosensory perception. Furthermore, the transcriptome data presented in this study may facilitate the studies on the molecular targets for controlling this harmful pest.