Genome-wide analysis reveals the expansion of Cytochrome P450 genes associated with xenobiotic metabolism in rice striped stem borer, Chilo suppressalis.

The Cytochrome P450 (CYP) superfamily is a large group of ancient proteins with enzymatic activities involved in various physiological processes. The rice striped stem borer, Chilo suppressalis, is an important insect pest in rice production. Here, we report the identification and characterization of 77 CYP genes from rice striped stem borer (SSB) through genome and transcriptome sequence analyses. All these CYP genes were confirmed by RT-PCR and direct sequencing. Twenty-eight CYP transcripts have full open reading frame (ORF) and four additional transcripts have a nearly full length coding region. The SSB CYP genes were classified into four clans, the mitochondrial, CYP2, CYP3, and CYP4. Phylogenetic analysis indicated that there was an apparent expansion of the CYP3 clan in insects. The CYP6AB subfamily of the CYP3 clan had nine members in SSB. Evolutionary analysis showed that this subfamily was expanded only in lepidopteran insects. In this study, we identified a new P450 subfamily, CYP321F, which is unique to SSB and located in the genome as tandem repeats. Our work provided a foundation for future studies on the functions and mechanism of P450s in the destructive rice pest.