Genome-wide analysis of chemosensory protein genes in the small white butterfly Pieris rapae (Lepidoptera: Pieridae)

Chemosensory proteins (CSPs) play a crucial role in olfactory recognition in insects. The small white butterfly Pieris rapae a major pest of Brassicaceae vegetables, which causes enormous economic losses uses olfaction to locate its host plants. However, the molecular mechanism of olfaction in this species remains unknown. Herein, we performed a genome-wide and transcriptome-wide analysis of CSP genes in P. rapae and identified 21 CSPs (PrapCSP1 to PrapCSP21). Proteins encoded by these genes showed typical characteristics of CSPs an N-terminal signal peptide and four positionally conserved cysteine residues. BLASTX analysis indicated that most P. rapae CSPs showed high amino acid identity with their respective orthologs in other lepidopterans. Phylogenetic analysis showed that most P. rapae CSPs were well segregated and were clustered into different branches. The 21 genes were located on six genomic scaffolds, and most genes were tandemly arrayed. Quantitative reverse transcription-PCR showed that PrapCSP3, 4, 16 and 21 had the highest expression level in the antennae; PrapCSP7 and PrapCSP18 were mainly expressed in the ovaries, and PrapCSP9 and PrapCSP17 were leg-enriched. PrapCSP11 and PrapCSP20 were found mainly in the heads and testes, respectively. Our findings provide a solid foundation for studying the function of these genes.