Properties of Mutant Acetolactate Synthases Resistant to Triazolopyrimidine Sulfonanilide

• Published in: Plant physiology (Bethesda) 1990-09, Vol.94 (1), p.239-244
• Main Authors: Mani V. Subramanian, Han-Yu Hung, Jennifer M. Dias, Virginia W. Miner, Butler, John H., John J. Jachetta
• Format: Article
• Language: English
• Subjects: Adaptation to environment and cultivation conditions; Agronomy. Soil science and plant productions; Amino acids; Biological and medical sciences; Branched chain amino acids; Chemicals; Cross resistance; Enzymes; Fundamental and applied biological sciences. Psychology; Genetics and breeding of economic plants; Herbicide resistance; Herbicides; Materials; Metabolism and Enzymology; Physiological regulation; Plants; Varietal selection. Specialized plant breeding, plant breeding aims
• ISSN: 0032-0889; 1532-2548
• DOI: 10.1104/pp.94.1.239

Triazolopyrimidine sulfanilides are a class of highly active herbicides whose primary target is acetolactate synthase. Spontaneous mutants of tobacco (Nicotiana tabacum) (KS-43) and cotton (Gossypium hirsutum) (PS-3 and DO-2) resistant to triazolopyrimidine sulfonanilide were selected in tissue culture. Acetolactate synthase partially purified from the three mutants were 80- to 1000-fold less sensitive to inhibition by the compound compared with the corresponding wild-type enzyme. The mutants also varied in the cross-resistance pattern to other acetolactate synthase inhibiting herbicides in the sulfonylurea, imidazolinone, and pyrimidyl-oxy-benzoate chemical families. Thus, acetolactate synthase from KS-43, PS-3, and DO-2 cultures have different mutations. The affinities for pyruvate, thiamine pyrophosphate, as well as the activity of the mutant enzymes were found to be comparable to the corresponding wild-type enzymes. However, the enzyme from PS-3 was highly resistant to feedback inhibition by valine and leucine. In contrast, acetolactate synthase from KS-43 and DO-2 were inhibited by valine and leucine to nearly the same extent as the wild-type enzymes. Also, PS-3 cultures accumulated much higher levels of the branched chain amino acids compared to the wild-type cotton culture. The mutation in the PS-3 enzyme has therefore rendered it insensitive to feedback regulation by valine and leucine.