ENGINEERING-PLANT RESISTANCE TO THIAZOPYR HERBICIDE VIA EXPRESSION OFA NOVEL ESTERASE DEACTIVATION ENZYME

Plants were engineered to confer resistance to thiazopyr, a member of the pyridine herbicide family, via an esterase deactivation mechanism. Earlier studies showed that transformation of thiazopyr to its monoac id metabolite resulted in loss of herbicidal activity (PC.C. Feng et a l., 1995, Xenobiotica 35, 27). Based on thiazopyr hydrolytic activity, a 60-kDa esterase was purified from rabbit liver. The N-terminal amin o acid sequence of purified pyridine-esterase demonstrated high homolo gy to the published protein sequence of rabbit liver esterase isozyme 1 (RLE1). PCR primers designed based on the amino acid sequence of RLE 1 recovered a novel cDNA (RLE3) whose derived amino acid sequence was 95% homologous to RLE1. Baculovirus-mediated expression of RLE3 cDNA i n insect cells detected the 60-kDa esterase as well as activity agains t thiazopyr. Stable plant transformation of RLE3 cDNA was conducted in tomato and tobacco under a constitutive expression promotor. R-0 plan ts demonstrated wild-type phenotype, and analysis of leaf tissues conf irmed the presence of the 60-kDa esterase. Transgenic seedlings demons trated both in vitro and in vivo deactivation of thiazopyr to the mono acid. In growth chamber and greenhouse tests, R-1 seedlings from trans genic tomato and tobacco demonstrated enhanced resistance to thiazopyr . Resistance was directly correlated to the level of pyridine-esterase expression. A field study was conducted with transgenic tomato seedli ngs Which further confirmed resistance to thiazopyr. (C) 1997 Academic Press.