The herbicide bromoxynil (3,5-dibromo-4-hydroxybenzonitrile) is a photosynthetic (photosystem II) inhibitor in plants.  A gene, bxn, encoding a specific nitrilase that converts bromoxynil to its primary metabolite 3,5-dibromo-4-hydroxybenzoic acid, was cloned from the natural soil bacterium Klebsiella ozaenae.  For expression in plants, the bxn gene was placed under control of a light-regulated tissue-specific promoter, the ribulose biophosphate carboxylase small subunit.  Transfer of this chimeric gene and expression of a bromoxynil-specific nitrilase in leaves of transgenic tobacco plants conferred resistance to high levels of a commercial formulation of bromoxynil.  The results presented indicate a successful approach to obtain herbicide resistance by introducing a novel catabolic detoxification gene in plants.