Herbicide Metabolism and Tolerance in the Transgenic Rice Plants Expressing Human CYP2C9 and CYP2C19

The cDNAs of human drug-metabolizing cytochrome P450 species CYP2C9 and CYP2C19 were each expressed in rice (Oryza sativa L.) plants under the control of CaMV35S promoter and Nos terminator. Western blot analysis of the selected transgenic rice plants revealed that CYP2C9 and CYP2C19 were produced in the transgenic rice plants 2C9-57 and 2C19-12, respectively. [14C]Chlorsulfuron and [14C]imazosulfuron were found to be more rapidly metabolized in R2 seedlings from 2C9-57R1 than in the control plants to yield polar metabolites which were mainly glucose conjugates of hydroxylated metabolites formed by the function of CYP2C9. The R2 transgenic rice seeds from 2C9-57R1 showed tolerance toward the sulfonylurea herbicide chlorsulfuron in a germination test. On the other hand, [14 [C]pyributicarb was also rapidly metabolized in R1 seedlings from 2C19-12R0 to give polar metabolites, but not in the control and PCR-negative transgenic plants. The R1 transgenic rice seeds of 2C19-12R0 showed cross-tolerance toward the herbicides mefenacet, metolachlor, norflurazon, and pyributicarb with different chemical structures and modes of herbicide action in a germination test. It was suggested that the herbicide-tolerant rice plant 2C9-57R2 seems to be practically useful for evasion of the sensitivity of rice plants toward the sulfonylurea herbicide chlorsulfuron. In addition, the herbicide-tolerant 2C19-12R1 appears to be potentially useful for the control of sulfonylurea-resistant weeds in a paddy field by the combined use of the herbicides mefenacet, metolachlor, norflurazon, and pyributicarb.