Characterization of multiple CYP9A genes in the silkworm, Bombyx mori

Abstract

Based on the advances in the silkworm genome project, a new genome-wide analysis of cytochrome P450 genes was performed, focusing mainly on gene duplication. All four CYP9A subfamily members from the silkworm, Bombyx mori, were cloned by RT-PCR and designated CYP9A19-CYP9A22 by the P450 Nomenclature Committee. They each contain an open reading frame of 1,593 bp in length and encode a putative polypeptide of 531 amino acids. Both nucleic acid and amino acid sequences share very high identities with one another. The typical motifs of insect cytochrome P450, including the heme-binding region, helix-C, helix-I, helix-K, and PERF, show high sequence conservation among the multiple proteins. Alignment with their cDNA sequences revealed that these paralogues share identical gene structures, each comprising ten exons and nine introns of variable sizes. The locations of their introns (all nine introns follow the GT-AG rule) are absolutely conserved. CYP9A19, CYP9A20, and CYP9A21 form a tandem cluster on chromosome 17, whereas CYP9A22 is separated from the cluster by four tandem alcohol-dehydrogenase-like genes. Their phylogenetic relationships and structural comparisons indicated that these paralogues arose as the results of gene duplication events. RT-PCR detected their mRNAs in different "first line of defense" tissues, as well as in several other organs, suggesting diverse functions. Tissue-selective expression also indicates their functional divergence. The identified CYP9A genes have not yet been found outside the Lepidoptera, and are probably unique to the Lepidoptera. They show high sequence and structural similarities to each other, indicating that the Lepidoptera-specific P450s may be of functional importance. This analysis constitutes the first report of the clustering, spatial organization, and functional divergence of P450 in the silkworm.

Independent Recruitment of a Flavin-Dependent Monooxygenase for Safe Accumulation of Sequestered Pyrrolizidine Alkaloids in Grasshoppers and Moths

“…Therefore, PA N -oxygenation in insects seems to be a unique feature of FMOs. Of note, CYPs in insects form a far larger gene family than FMOs (the genomes of D. melanogaster and B. mori encode 83 and 86 putative CYPs, respectively, in contrast to only 2 and 3 putative FMOs, respectively [12], [17], [31], [32]) and are well-known for their importance in the metabolism of natural and artificial xenobiotics, including insecticides [33]. Specific and inducible CYP-encoding genes in Papilio butterflies (Papilionidae, Lepidoptera) for the detoxification of furanocoumarins represent only one of several fascinating examples of gene evolution during adaptation of insects to plant allelochemicals [34], [35].…”

Identification and characterization of a novel chitinase-like gene cluster (AgCht5) possibly derived from tandem duplications in the African malaria mosquito, Anopheles gambiae

“…Tandem duplicates are copies of a nearby gene that are within short intron distances of each other and may harbor some interesting biology. Gene expansion by tandem duplication is common in cytochrome P450 gene evolution (Ai et al, 2010;Baldwin et al, 2009). Five AgCht5 genes are clustered together in chromosome 2R with no other intervening genes.…”

Genome-wide analysis of cytochrome P450 monooxygenase genes in the silkworm, Bombyx mori

“…In general terms the intron positions of the silkworm members of the ubiquitous CYP3 and CYP4 clans are highly conserved and show very strong clade-specificity. For instance, 19 members from a clade composed of CYP340 and -341 families as well as CYP366A1 and -4AU2, and 7 members from the other clade formed by CYP9 families (Ai et al, 2010), they share nearly identical structures, respectively. All 14 CYP6 genes also have a single conserved intron at the second glycin of heme-binding motif, as was also observed for Helicoverpa armigera CYP6B P450s (Grubor and Heckel, 2007).…”