Analysis of substrate specificity of pig CYP2B22 and CYP2C49 towards herbicides by transgenic rice plants.

We introduced two novel types of pig (Sus scrofa) cytochrome P450, CYP2B22 and CYP2C49, into rice plants (Oryza sativa L. cv. 'Nipponbare') to produce herbicide-tolerant plants and to confirm the metabolic activities of the cytochrome P450 species. In germination tests, both types of transgenic plants showed tolerance to various herbicides with different modes of action. CYP2B22 rice plants showed tolerance towards 12 herbicides including chlortoluron (100 microM), amiprofos-methyl (2.5 microM), pendimethalin (10 microM), metolachlor (2.5 microM), and esprocarb (20 microM). CYP2C49 rice plants showed tolerance towards 13 herbicides, including chlortoluron (100 microM), norflurazon (0.5 microM), amiprofos-methyl (2.5 microM), alachlor (0.8 microM), and isoxaben (1 microM). The herbicide tolerance was considered to reflect the substrate specificity of the introduced P450 species. We used (14)C-labeled metolachlor and norflurazon to confirm the P450 activity in the transgenic rice plants. The herbicides were metabolized more quickly in the transgenic rice plants than in the nontransgenic rice plants. Therefore, CYP2B22 and CYP2C49 rice plants became more tolerant to various herbicides than nontransgenic control plants because of accelerated metabolism of the herbicides by the introduced P450 species. Assuming that public and commercial acceptance is forthcoming, these transgenic rice plants may become useful tools for the breeding of herbicide-tolerant crops.