Rhizobium tropici Genes Involved in Free-Living Salt Tolerance are Required for the Establishment of Efficient Nitrogen-Fixing Symbiosis with Phaseolus vulgaris
Open Access
- 1 March 2002
- journal article
- research article
- Published by Scientific Societies in Molecular Plant-Microbe Interactions®
- Vol. 15 (3), 225-232
- https://doi.org/10.1094/mpmi.2002.15.3.225
Abstract
Characterization of nine transposon-induced mutants of Rhizobium tropici with decreased salt tolerance (DST) allowed the identification of eight gene loci required for adaptation to high external NaCl. Most of the genes also were involved in adaptation to hyperosmotic media and were required to overcome the toxicity of LiCl. According to their possible functions, genes identified could be classified into three groups. The first group included two genes involved in regulation of gene expression, such as ntrY, the sensor element of the bacterial ntrY/ntrX two-component regulatory system involved in regulation of nitrogen metabolism, and greA, which encodes a transcription elongation factor. The second group included genes related to synthesis, assembly, or maturation of proteins, such as alaS coding for alanine-tRNA synthetase, dnaJ, which encodes a molecular chaperone, and a nifS homolog probably encoding a cysteine desulfurase involved in the maturation of Fe-S proteins. Genes related with cellular build-up and maintenance were in the third group, such as a noeJ-homolog, encoding a mannose-1-phosphate guanylyltransferase likely involved in lipopolysaccharide biosynthesis, and kup, specifying an inner-membrane protein involved in potassium uptake. Another gene was identified that had no homology to known genes but that could be conserved in other rhizobia. When inoculated on Phaseolus vulgaris growing under nonsaline conditions, all DST mutants displayed severe symbiotic defects: ntrY and noeJ mutants were impaired in nodulation, and the remaining mutants formed symbiosis with very reduced nitrogenase activity. The results suggest that bacterial ability to adapt to hyper-osmotic and salt stress is important for the bacteroid nitrogen-fixing function inside the legume nodule and provide genetic evidence supporting the suggestion that rhizobia face severe environmental changes after their release into plant cells.Keywords
This publication has 51 references indexed in Scilit:
- Genome structure of Ri plasmid (2). Sequencing analysis of T-DNA and its flanking regions of pRi1724 in Japanese Agrobacterium rhizogenesEncyclopedia of Life Sciences, 1999
- DnaJ Potentiates the Interaction between DnaK and α-Helical PeptidesBiochemical and Biophysical Research Communications, 1997
- The dnaKJ operon belongs to the σ32-dependent class of heat shock genes in Bradyrhizobium japonicumMolecular Genetics and Genomics, 1997
- Characterization ofRhizobium tropiciClAT899 Nodulation Factors: The Role ofnodHandnodPQGenes in Their SulfationMolecular Plant-Microbe Interactions®, 1996
- Acid pH tolerance in strains of Rhizobium and Bradyrhizobium, and initial studies on the basis for acid tolerance of Rhizobium tropici UMR1899Canadian Journal of Microbiology, 1994
- Nodulation factors from Rhizobium tropici are sulfated or nonsulfated chitopentasaccharides containing an N-methyl-N-acylglucosaminyl terminusBiochemistry, 1993
- Homology of the NifS family of proteins to a new class of pyridoxal phosphate‐dependent enzymesFEBS Letters, 1993
- A Broad Host Range Mobilization System for In Vivo Genetic Engineering: Transposon Mutagenesis in Gram Negative BacteriaBio/Technology, 1983
- Detection of specific sequences among DNA fragments separated by gel electrophoresisJournal of Molecular Biology, 1975
- Indole-3-acetic Acid Catabolism by Soybean BacteroidsJournal of General Microbiology, 1975