Transgenic rice plants expressing human CYP1A1 exude herbicide metabolites from their roots

Abstract

We introduced a human cytochrome P450 CYP1A1 gene into rice plants ( Oryza sativa cv. Nipponbare) to confer herbicide tolerance. In germination tests, the R 1 seeds showed tolerance to various herbicides with different modes of action, including quizalofop-ethyl (0.2 μM), norflurazon (0.5 μM), mefenacet (2.5 μM), and chlortoluron (100 μM). We used 14C-labeled atrazine, chlortoluron, and norflurazon to confirm the metabolism of herbicides by the action of the introduced CYP1A1. Although both CYP1A1 plants and nontransgenic control plants metabolized these herbicides into the same set of chemical compounds, the herbicides were metabolized more rapidly in the CYP1A1 plants. We were surprised to find that the levels of the intermediate metabolites were higher in the culture medium of the CYP1A1 plants than in the plants themselves, because it is commonly accepted that herbicides are taken up, metabolized, and stored in plants. The metabolites of herbicides seemed to be exuded into the medium from the roots of the CYP1A1 plants. The introduced P450 enhanced the metabolism of the herbicides in plants. Therefore, the CYP1A1 plants became more tolerant to various herbicides than the control plants.