PLANT EXPRESSION OF A BACTERIAL CYTOCHROME-P450 THAT CATALYZES ACTIVATION OF A SULFONYLUREA PRO-HERBICIDE

The Streptomyces griseolos gene encoding herbicide-metabolizing cytoch rome P450(SU1) (CYP105A1) was expressed in transgenic tobacco (Nicotia na tabacum). Because this P450 can be reduced by plant chloroplast fer redoxin in vitro, chloroplast-targeted and nontargeted expression were compared. Whereas P450(SU1) antigen was found in the transgenic plant s regardless of the targeting, only those with chloroplast-directed en zyme performed P450(SU1)-mediated N-dealkylation of the sulfonylurea y l]-1,2-benzoisothiazole-7-sulfonamide-1,1-dioxide (R7402). Chloroplast targeting appears to be essential for the bacterial P450 to function in the plant. Because the R7402 metabolite has greater phytotoxicity t han R7402 itself, plants bearing active P450(SU1) are susceptible to i njury from R7402 treatment that is harmless to plants without P450(SU1 ). Thus, P450(SU1) expression and R7402 treatment can be used as a neg ative selection system in plants. Furthermore, expression of P450(SU1) from a tissue-specific promoter can sequester production of the phyto toxic R7402 metabolite to a single plant tissue. In tobacco expressing P450(SU1) from a tapetum-specific promoter, treatment of immature flo wer buds with R7402 caused dramatically lowered pollen viability. Such treatment could be the basis for a chemical hybridizing agent.