Effect of mutagenesis at serine 653 of Arabidopsis thaliana acetohydroxyacid synthase on the sensitivity to imidazolinone and sulfonylurea herbicides

Resistance to sulfonylurea and imidazolinone herbicides can occur by mutati ons in acetohydroxyacid synthase (EC 4.1,3.18), Changing serine 653 to aspa ragine is known to cause insensitivity to imidazolinones but not to sulfony lureas. Here, S-653 of the Arabidopsis thaliana enzyme was mutated to alani ne, threonine and phenylalanine. The purified mutated enzymes resemble wild -type in their enzymatic properties. The threonine and phenylalanine mutant s are imidazolinone-resistant and the latter is also slightly sulfonylurea- resistant. The alanine mutant remains sensitive to both herbicides. The res ults suggest that the beta-hydroxyl group is not required for imidazolinone binding and that the size of the side-chain determines resistance. (C) 199 9 Federation of European Biochemical Societies.