L-O-methylthreonine-resistant mutant of Arabidopsis defective in isoleucine feedback regulation

• Published in: Plant physiology (Bethesda) Vol. 107; no. 1; pp. 43 - 52
• Main Authors: Mourad, G. (Indiana-Purdue University, Fort Wayne, IN.), King, J
• Format: Journal Article
• Language: English
• Published: Rockville, MD American Society of Plant Physiologists 01.01.1995
• Subjects: ACIDE AMINE; ACTIVIDAD ENZIMATICA; ACTIVITE ENZYMATIQUE; Agronomy. Soil science and plant productions; Alleles; Amino acids; AMINOACIDOS; ARABIDOPSIS THALIANA; Biological and medical sciences; BIOSINTESIS; BIOSYNTHESE; Biosynthesis; Chromosomes; Classical and quantitative genetics. Population genetics. Molecular genetics; CRECIMIENTO; CROISSANCE; Enzymes; EXPRESION GENICA; EXPRESSION DES GENES; Fundamental and applied biological sciences. Psychology; GENE; Gene Regulation and Molecular Genetics; Generalities. Genetics. Plant material; GENES; GENETICA; Genetics and breeding of economic plants; GENETIQUE; INHIBIDORES DE ENZIMAS; INHIBITEUR D'ENZYME; ISOLEUCINA; ISOLEUCINE; LIASAS; LIGNEE CONSANGUINE; LINEAS CONSANGUINEAS; LYASE; MARCADORES GENETICOS; MARQUEUR GENETIQUE; Molecular genetics; MUTANT; MUTANTES; Plant growth; Plants; Seedlings; Segregation; THREONINE; TREONINA; Enzyme; Feedback regulation; Threonine dehydratase; Lyases; Arabidopsis thaliana; Resistance; Biochemical properties; Cruciferae; Dicotyledones; Aminoacid; Angiospermae; Spermatophyta; Inhibition; Mutation; Experimental plant; Carbon-oxygen lyases; Derived product; Hydro-lyases; Isoleucine
• ISSN: 0032-0889; 1532-2548
• DOI: 10.1104/pp.107.1.43

Threonine dehydratase/deaminase (TD), the first enzyme in the isoleucine biosynthetic pathway, is feedback inhibited by isoleucine. By screening M2 populations of ethyl methane sulfonate-treated Arabidopsis thaliana Columbia wild-type seeds, we isolated five independent mutants that were resistant to L-O-amethylthreonine, an isoleucine structural analog. Growth in the mutants was 50- to 600-fold more resistant to L-O-amethylthreonine than in the wild type. The resistance was due to a singie, dominant nuclear gene that was denoted omrl and was mapped to chromosome 3 in GM1 1b, the mutant line exhibiting the highest level of resistance. Biochemical characteristics (specific activities, Km, Vmax, and pH optimum) of TD in extracts from the wild type and GM1 1b were similar except for the inhibition constant of isoleucine, which was 50-fold higher in GM11b than in the wild type. Levels of free isoleucine were 20-fold higher in extracts from GMllb than in extracts from wild type. Therefore, isoleucine feedback insensitivity in GM11b is due to a mutant form of the TD enzyme encoded by omr1. The mutant allele omrl of the line GM11b could provide a new selectable marker for plant genetic transformation