Cytochrome P450 Monooxygenases Metabolizing Herbicides

Cytochrome P450 monooxygenases catalyze oxidative reactions in biosynthesis of secondary metabolites as well as in metabolism of xenobiotics in higher plants. The enzyme system localized on the microsomes of plant cells consists of many cytochrome P450 (P450 or CYP) species and one or a few species of NADPH-cytochrome P450 reductase (P450 reductase). Particularly, P450 species metabolizing herbicides play an important role in r herbicide selectivity and resistance. However, molecular information on plant P450 species metabolizig herbicides was quite limited. It. was found that tobacco cultured S401 cells treated with 2,4-D metabolized chlortoluron to give ring-methyl hydroxylated and N-demethylated metabolites. Then, we cloned P450 cDNAs from the S401 cells treated with 2,4-D by RT-PCR methods. Among four novel P450 cDNA clones, CYP71A11 and CYP81B2 were each expressed in the yeast Saccharomyces cerevisiae and were found to catalyze both ring-methyl hydroxylation and N-demethylation of chlortoluron, and ring-methylhydroxylation, respectively. It was also found that several mammalian P450 species including human P4501A1 metabolized chlortoluron through ring-methyl hydroxylation and N-demethylation, and atrazine through N-deal- kylation. When rat P450IA1 (CYP 1 Al) and its fused enzyme with yeast P450 reductase were each expressed in potato and tobacco plants, respectively, both transgenic plants showed resistance to the herbicides chlortoluron. Expression of a mammalian P450 species with overlapping broad substrate-specificity towards xenobiotics in plants seems to produce transgenic plants not only resistant to herbicides but also enhanced in metabolism of various environmental contaminants.