Cytochrome P450 monooxygenases play a significant role in the detoxification of hostplant allelochemicals and synthetic insecticides in Lepidoptera. In Helicoverpa zea, a polyphagous noctuid of economic importance, metabolisms of xanthotoxin, a toxic furanocoumarin, and cypermethrin, an insecticide, are mediated by at least one P450 whose catalytic site is capable of accepting both substrates. Closely related P450s in the CYP6B subfamily (CYP6B8, CYP6B9, CYP6B27, CYP6B28) and in the divergent CYP4 family potentially contribute to the detoxification of xenobiotic chemicals by this species. To date, we have cloned all four of the CYP6B subfamily members and two CYP4 family members expressed in this species. RT-PCR analysis of RNAs isolated from various developmental stages and tissues has demonstrated that all four of the CYP6B genes are expressed at a discernible levels in uninduced midguts of fifth instar larvae as well as intact larvae of all earlier stages. Induction analysis indicates that these four CYP6B transcripts accumulate to varying degrees in response to a range of chemicals naturally encountered in the hostplants for these larvae (xanthotoxin, indole-3-carbinol, chlorogenic acid, etc.) as well as synthetic chemicals not naturally encountered (insecticides, phenobarbitol, etc.). CYP4 transcripts also accumulate in response to xanthotoxin. We are in the process of further defining the substrate reactivities of these CYP6B and CYP4 proteins toward natural and synthetic chemicals and on defining interactions among the various chemical inducers of the CYP6B and CYP4 genes.
Species 1: Lepidoptera Noctuidae Helicoverpa zea (corn earworm)
Keywords: P450 gene expression, detoxification of xenobiotic chemicals
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