Genetic analysis and phenotypic characterization of three novel genes of Rhizobium tropici CIAT899 involved in symbiotic interactions with Phaseolus vulgaris

Rhizobium tropici CIAT899 is highly tolerant to many environmental stresses and a good competitor for nodule occupancy of Phaseolus vulgaris. Random transposon mutagenesis was performed with the aim to identify novel genes of this strain involved in symbiosis and stress tolerance. The analysis of th...

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Bibliographic Details
Main Author: Rojas Jimenez, Keilor
Contributors: Werner, Dietrich (Prof. Dr.) (Thesis advisor)
Format: Doctoral Thesis
Language:English
Published: Philipps-Universität Marburg 2005
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Summary:Rhizobium tropici CIAT899 is highly tolerant to many environmental stresses and a good competitor for nodule occupancy of Phaseolus vulgaris. Random transposon mutagenesis was performed with the aim to identify novel genes of this strain involved in symbiosis and stress tolerance. The analysis of the locus disrupted by the Tn5 insertion in mutants 899-PV9 and 899-PV4 led the discovery of three novel genes required for and efficient symbiotic interaction with beans plants. The first gene (syc1) bears significant similarity to voltage-gated chloride channels. A non-polar deletion in this gene caused serious deficiencies for nodule establishment, nodulation competitiveness and N2 fixation, probably due to its reduced ability to invade plant cells and to form stable symbiosomes, as judged by electron transmission microscopy. A second gene (olsC) found downstream of the former was shown to be homologous with aspartyl/asparaginyl β-hydroxylases and involved in the modification of two species of ornithine-containing lipids, presumably by a hydroxylation. A mutant carrying a non-polar deletion in olsC was symbiotically defective, whereas over-expressed OlsC in the complemented strain was related with an acid-sensitive phenotype. The third gene (sigE) codes for a putative σE factor. Analysis performed on the mutant carrying a deletion in this gene also revealed serious deficiencies for nodule development, nodulation competitiveness and N2 fixation when inoculated on bean plants. These three different bacterial activities have not been previously reported as required for the symbiotic interaction of rhizobia with its legume host.
DOI:10.17192/z2005.0119