Abstract
BackgroundTransposons, i.e. transposable elements (TEs), are the major internal spontaneous mutation agents for the variability of eukaryotic genomes. To address the general issue of whether transposons mediate genomic changes in environment-adaptation genes, we scanned two alleles per each of the six xenobiotic-metabolizing Helicoverpa zea cytochrome P450 loci, including CYP6B8, CYP6B27, CYP321A1, CYP321A2, CYP9A12v3 and CYP9A14, for the presence of transposon insertions by genome walking and sequence analysis. We also scanned thirteen Drosophila melanogaster P450s genes for TE insertions by in silico mapping and literature search.ResultsTwelve novel transposons, including LINEs (long interspersed nuclear elements), SINEs (short interspersed nuclear elements), MITEs (miniature inverted-repeat transposable elements), one full-length transib-like transposon, and one full-length Tcl-like DNA transpson, are identified from the alleles of the six H. zea P450 genes. The twelve transposons are inserted into the 5'flanking region, 3'flanking region, exon, or intron of the six environment-adaptation P450 genes. In D. melanogaster, seven out of the eight Drosophila P450s (CYP4E2, CYP6A2, CYP6A8, CYP6A9, CYP6G1, CYP6W1, CYP12A4, CYP12D1) implicated in insecticide resistance are associated with a variety of transposons. By contrast, all the five Drosophila P450s (CYP302A1, CYP306A1, CYP307A1, CYP314A1 and CYP315A1) involved in ecdysone biosynthesis and developmental regulation are free of TE insertions.ConclusionThese results indicate that TEs are selectively retained within or in close proximity to xenobiotic-metabolizing P450 genes.
Highlights
Transposons, i.e. transposable elements (TEs), are the major internal spontaneous mutation agents for the variability of eukaryotic genomes
Transposons within the CYP6B gene cluster Seven P450 monooxygenases (P450s) genes distributed in the CYP6B, CYP4M, and CYP321A subfamilies have been cloned from H. zea [2123]
Previous studies have demonstrated that CYP321A1 is highly inducible by xanthotoxin [23] and the four CYP6B transcripts accumulate to varying degrees in response to a range of allelochemicals naturally encountered in hostplants as well as in response to synthetic chemicals not naturally encountered [21,22]
Summary
Transposons, i.e. transposable elements (TEs), are the major internal spontaneous mutation agents for the variability of eukaryotic genomes. All organisms must adapt to their environments composed of biotic and abiotic factors to survive and reproduce. This requires organisms to allocate a substantial portion of their genomes to encode environment response genes that can be defined as those involved in interactions external to the organisms [1]. To cope with the ever-changing environment, organisms are required to have greater genomic plasticity in the environmental response genes so that novel adaptive genomic changes (mutations) are available for natural selection. BMC Evolutionary Biology 2007, 7:46 http://www.biomedcentral.com/1471-2148/7/46 directly cause genomic changes, the majority of environmental factors act as pure selection agents rather than mutagens. The genomic plasticity necessary for coping with the ever-changing environment in these loci should arise primarily from internal spontaneous alteration events [2]
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