The product of the Rhizobium meliloti ilvC gene is required for isoleucine and valine synthesis and nodulation of alfalfa

• Published in: Journal of Bacteriology Vol. 173; no. 24; pp. 7756 - 7764
• Main Authors: Aguilar, O.M. (Forestry Canada, Edmonton, Alberta, Canada), Grasso, D.H
• Format: Journal Article
• Language: English
• Published: Washington, DC American Society for Microbiology 01-12-1991
• Subjects: Alcohol Oxidoreductases - genetics; Alcohol Oxidoreductases - metabolism; Amino Acid Sequence; Bacteriology; Base Sequence; Biological and medical sciences; BIOSINTESIS; BIOSYNTHESE; Cloning, Molecular; DNA, Bacterial; Escherichia coli - genetics; FORMATION DE NODOSITES; Fundamental and applied biological sciences. Psychology; GENE; GENES; Genes, Bacterial; Genetic Complementation Test; ISOLEUCINA; ISOLEUCINE; Isoleucine - biosynthesis; Ketol-Acid Reductoisomerase; MEDICAGO SATIVA; Medicago sativa - microbiology; Metabolism. Enzymes; Microbiology; Molecular Sequence Data; Nitrogen Fixation - genetics; NODULACION; NUCLEOTIDE; NUCLEOTIDOS; OXIDORREDUCTASAS; OXYDOREDUCTASE; Phenotype; RHIZOBIUM MELILOTI; Sequence Alignment; Sinorhizobium meliloti - enzymology; Sinorhizobium meliloti - genetics; VALINA; VALINE; Valine - biosynthesis; Rhizobium meliloti; Nucleotide sequence; Enzyme; Sequence alignment; Medicago sativa; Nodulation; Homology; Biosynthesis; Leguminosae; Enzymatic activity; Valine; Dicotyledones; Angiospermae; Restriction map; Bacteria; Ketol-acid reductoisomerase; Spermatophyta; Rhizobiaceae; Aminoacid sequence; Isoleucine
• ISSN: 0021-9193; 1098-5530; 1067-8832
• DOI: 10.1128/jb.173.24.7756-7764.1991

Tn5-induced mutants of Rhizobium meliloti that require the amino acids isoleucine and valine for growth on minimal medium were studied. In one mutant, 1028, the defect is associated with an inability to induce nodules on alfalfa. The Tn5 mutation in 1028 is located in a chromosomal 5.5-kb EcoRI fragment. Complementation analysis with cloned DNA indicated that 2.0 kb of DNA from the 5.5-kb EcoRI fragment restored the wild-type phenotype in the Ilv- Nod- mutant. This region was further characterized by DNA sequence analysis and was shown to contain a coding sequence homologous to those for Escherichia coli IlvC and Saccharomyces cerevisiae Ilv5. Genes ilvC and ilv5 code for the enzyme acetohydroxy acid isomeroreductase (isomeroreductase), the second enzyme in the parallel pathways for the biosynthesis of isoleucine and valine. Enzymatic assays confirmed that strain 1028 was a mutant defective in isomeroreductase activity. In addition, it was shown that the ilvC genes of Rhizobium meliloti and E. coli are functionally equivalent. We demonstrated that in ilvC mutant 1028 the common nodulation genes nodABC are not activated by the inducer luteolin. E. coli ilvC complemented both defective properties (Ilv- and Nod-) found in mutant 1028. These findings demonstrate that R. meliloti requires an active isomeroreductase enzyme for successful nodulation of alfalfa