Abstract:

Cytochrome P450 plays a dominant role in the metabolism of a wide variety of both endogenous and xenobiotic substances. The evolution of P450 gene function was analyzed in the genome of the pea aphid, Acyrthosiphon pisum, using the mRNA and amino acid data. A genome-wide analysis of P450 genes was performed in pea aphid genome by bioinformatical methods. The results showed that sixty-nine P450 genes were discovered in pea aphid genome, which are of a typical superfamily and belong to 13 families and 18 subfamilies. We collected expression sequence tag (EST) evidence for 39 putative P450s genes, which are expressed at the transcriptional level and more likely to be true P450s. Because of significant differences in gene sequences, among 69 P450 genes 18 genes could not partitioned into any group, while the rest 51 P450 genes were partitioned into 10 groups by a criterion that the genes belong to a group when their amino acid identity is more than 60%. Positive selection and gene conversion were analyzed in 8 groups (including 47 genes). Positive selection was detected in only one group (including 9 genes). The positively selected sites with a more than 95% probability were 20T and 27N, located in substrate recognition site (SRS1) and D-helix, respectively. The significant gene conversion events were detected in 3 groups (8 sequences). P450 genes that identified gene conversion events were members of CYP4 family, which were CYP4C, CYP4G and CYP4V subfamily, respectively. Protein similarity between P450 genes with gene conversion was 70%-95%. P450 genes with gene conversion lay in the same scaffold, e.g., M_001944991 and XM_001951794 lay in SCAFFOLD12542, while XM_001945510 and XM_001944057 lay in SCAFFOLD7010. The results suggest that P450 genes may gain new function through gene duplication and gene conversion. Moreover, twenty motifs were identified, of which 5 motifs existed in over 90% of P450 genes.

Key words: Acyrthosiphon pisum, P450, expression sequence tag (EST), positive selection, gene conversion, motif