Identification and comparative expression analysis of odorant binding protein genes in the tobacco cutworm Spodoptera litura

Insect odorant binding proteins (OBPs) are thought to involve in insects' olfaction perception. In the present study, we identified 38 OBP genes from the antennal transcriptomes of Spodoptera litura. Tissue expression profiles analysis revealed that 17 of the 38 SlitOBP transcripts were uniquely or primarily expressed in the antennae of both sexes, suggesting their putative role in chemoreception. The RPKM value analysis revealed that seven OBPs (SlitPBP1-3, SlitGOBP1-2, SlitOBP3 and SlitOBP5) are highly abundant in male and female antennae. Most S. litura antennal unigenes had high homology with Lepidoptera insects, especially genes of the genus Spodoptera. Phylogenetic analysis of the Lepidoptera OBPs demonstrated that the OBP genes from the genus Spodoptera (S. litura, Spodoptera littoralis and Spodoptera exigua) had a relatively close evolutionary relationship. Some regular patterns and key conserved motifs of OBPs in genus Spodoptera are identified by MEME, and their putative roles in detecting odorants are discussed here. The motif-patterns between Lepidoptera OBPs and CSPs are also compared. The SlitOBPs identified here provide a starting point to facilitate functional studies of insect OBPs at the molecular level both in vivo and in vitro.