|NIU, GUODONG - University Of Illinois|
|RUPASINGHE, SANJEEWA - University Of Illinois|
|ZANGERL, ARTHUR - University Of Illinois|
|SCHULER, MARY - University Of Illinois|
|BERENBAUM, MAY - University Of Illinois|
Submitted to: Insect Biochemistry and Molecular Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/31/2010
Publication Date: 4/1/2011
Citation: Niu, G., Rupasinghe, S.G., Zangerl, A.R., Siegel, J.P., Schuler, M.A., Berenbaum, M.R. 2011. A substrate-specific cytochrome P450 monoxygenase, CYP6AB11, from the polyphagous navel orangeworm. Insect Biochemistry and Molecular Biology. 41:244-253.
Interpretive Summary: The navel orangeworm, Amyelois transitella (Walker)is a serious pest of many tree crops in California, including almonds, pistachios, walnuts and figs. In order to promote better control of this insect pest, a study was conducted to understand the mechanisms by which this insect detoxifies the defense compounds present in plants. The method used in this study extracted DNA from larval midgets and identified genes from the cytochrome P450 complex, a major metabolic route that insects use to detoxify various plant defense compounds. We determined the range of activity of one gene identified in this study, designated as CYP6AB11. The navel orangeworm is considered a generalist feeder, and we expected that this enzyme would oxidize entire classes of defensive chemicals. Instead, CYP6AB11 specifically and rapidly inactivated a plant defensive compound called imperatorin. This finding suggests that imperatorin was present in the original host that the navel orangeworm evolved on. This same gene enabled the navel orangeworm to break down at a slower rate a different chemical, piperonyl butoxide, which is used to make the pyrethroid class of insecticides more potent. From this study we conclude that the navel orangeworm evolved on plants or a plant family containing imperatorin, and that this insect possesses the capability to become resistant to insecticides utilizing piperonyl butoxide.
Technical Abstract: The navel orangeworm, Amyelois transitella (Walker)is a serious pest of many tree crops in California, including almonds, pistachios, walnuts and figs. In order to understand the molecular mechanisms underlying detoxification of phytochemicals, insecticides, and mycotoxins by this species, full length CYP6AB11 cDNA was isolated from larval midgets using RACE PCR. Phylogenetic analysis of this insect’s cytochrome P450 monooxygenases established its evolutionary relationship to other species because of its ability to selectively metabolize imperatorin, a linear furanocoumarin, and myrisiticin, a natural methylendioxyphenyl compound. Metabolic assays conducted with baculovirus expressed P450 protein, P450 reductase and cytochrome b5 on 16 compounds, including phytochemicals, mycotoxins and synthetic pesticides, indicated that CYP6AB11 efficiently metabolized imperatorin and slowly metabolized piperonyl butoxide. LC-MS analysis indicated that the imperatorin metabolite is an epoxide generated by oxidation of the double bond in its extended isoprenyl side chain. Predictive structures for CYP6AB11 suggested that its catalytic site contains a doughnut-like constriction over the heme that excludes aromatic rings on substrates and allows only their extended side chains to access the catalytic site.