Plant Expression of a Bacterial Cytochrome P450 That Catalyzes Activation of a Sulfonylurea Pro-Herbicide

Abstract

The Sfreptomyces griseolus gene encoding herbicide-metabolizing cytochrome P450sul (CYP105Al) was expressed in transgenic tobacco (Nicofiana tabacum). Because this P450 can be reduced by plant chloroplast ferredoxin in vitro, chloroplast-targeted and nontargeted expression were compared. Whereas P450sul antigen was found in the transgenic plants regardless of the targeting, only those with chloroplast-directed enzyme performed P450sul-mediated N-dealkylation of the sulfonylurea 2-methylethyl-2,3-dihydro-N-[(4,6-dimethoxypyrimidin-2-yl)aminocarbonyl~-1,2-benzoisothiazole-7-sulfonamide-1,l-dioxide (R7402). Chloroplast targeting appears to be essential for the bacterial P450 to function in the plant. Because the R7402 metabolite has greater phytotoxicity than R7402 itself, plants bearing active P450sul are susceptible to injury from R7402 treatment that is harmless to plants without P45OSul. Thus, P450sul expression and R7402 treatment can be used as a negative selection system in plants. Furthermore, expression of P450sul from a tissue-specific promoter can sequester production of the phytotoxic R7402 metabolite to a single plant tissue. In tobacco expressing P450sul from a tapetum-specific promoter, treatment of immature flower buds with R7402 caused dramatically lowered pollen viability. Such treatment could be the basis for a chemical hybridizing agent.P450 monooxygenases play a central role in plant response to a variety of environmental challenges, including herbicide and other pesticide treatments (Cole, 1983;Durst, 1991). The best examples of this role are those P450s that can chemically alter an herbicide to a form with reduced phytotoxicity, resulting in much higher herbicide tolerance in the plant where this metabolism occurs (Frear et al., 1969(Frear et al., ,1991Sweetser et al., 1982; Jacobson and Shimabukuru, 1984;Brown, 1990). Significant variability in P450 enzyme activity exists among plant species, both in the presence of distinct enzymic forms and in their range of substrate specificity. This variability is a major determinant in herbicide selectivity, the differential herbicide sensitivity of weed and crop species. Altering herbicide selectivity, particularly confemng resistance in a crop plant, might be accomplished by expression of Present address:

Impaired sucrose‐induction mutants reveal the modulation of sugar‐induced starch biosynthetic gene expression by abscisic acid signalling

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Multiple Independent Defective Suppressor-mutator Transposon Insertions in Arabidopsis: A Tool for Functional Genomics

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