Immunogold localisation of hemoglobin inCasuarina root nodules

Abstract The enzyme phosphoenolpyruvate carboxykinase (Pck) catalyzes the first step in the gluconeogenic pathway in most organisms. We are examining the genetic regulation of the gene encoding Pck, pckA, in Rhizobium (now Sinorhizobium) meliloti. This bacterium forms N2-fixing root nodules on alfalfa, and the major energy sources supplied to the bacteria within these nodules are C4-dicarboxylic acids such as malate and succinate. R. meliloti cells growing in glucose minimal medium show very low pckA expression whereas addition of succinate to this medium results in a rapid induction of pckA transcription. We identified spontaneous mutations (rpk) that alter the regulation of pckA expression such that pckA is expressed in media containing the non-inducing carbon sources lactose and glucose. Genetic and phenotypic analysis allowed us to differentiate at least four rpk mutant classes that map to different locations on the R. meliloti chromosome. The wild-type locus corresponding to one of these rpk loci was cloned by complementation, and two Tn5 insertions within the insert DNA that no longer complemented the rpk mutation were identified. The nucleotide sequence of this region revealed that both Tn5 insertions lay within a gene encoding a protein homologous to the Ga1R/LacI family of transcriptional regulators that are involved in metabolism.

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Equilibria and Kinetics of Ligand Binding by Leghemoglobin from Soybean Root Nodules

Journal of Biological Chemistry ◽

10.1016/s0021-9258(19)45733-5 ◽

1972 ◽

Vol 247 (2) ◽

pp. 521-526

Author(s):

Takashi Imamura ◽

Austen Riggs ◽

Quentin H. Gibson

Keyword(s):

Ligand Binding ◽

Root Nodules ◽

Soybean Root ◽

Kinetics Of

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Mutation in the ntrR Gene, a Member of the vap Gene Family, Increases the Symbiotic Efficiency of Sinorhizobium meliloti

Molecular Plant-Microbe Interactions ◽

10.1094/mpmi.2001.14.7.887 ◽

2001 ◽

Vol 14 (7) ◽

pp. 887-894 ◽

Cited By ~ 25

Author(s):

Boglárka Oláh ◽

Erno Kiss ◽

Zoltán Györgypál ◽

Judit Borzi ◽

Gyöngyi Cinege ◽

...

Keyword(s):

Nitrogen Fixation ◽

Pathogenic Bacteria ◽

Sinorhizobium Meliloti ◽

Root Nodules ◽

Nifh Gene ◽

Dry Weight ◽

Nodule Occupancy ◽

Gene Encoding ◽

Symbiotic Efficiency ◽

Host Interactions

In specific plant organs, namely the root nodules of alfalfa, fixed nitrogen (ammonia) produced by the symbiotic partner Sinorhizobium meliloti supports the growth of the host plant in nitrogen-depleted environment. Here, we report that a derivative of S. meliloti carrying a mutation in the chromosomal ntrR gene induced nodules with enhanced nitrogen fixation capacity, resulting in an increased dry weight and nitrogen content of alfalfa. The efficient nitrogen fixation is a result of the higher expression level of the nifH gene, encoding one of the subunits of the nitrogenase enzyme, and nifA, the transcriptional regulator of the nif operon. The ntrR gene, controlled negatively by its own product and positively by the symbiotic regulator syrM, is expressed in the same zone of nodules as the nif genes. As a result of the nitrogen-tolerant phenotype of the strain, the beneficial effect of the mutation on efficiency is not abolished in the presence of the exogenous nitrogen source. The ntrR mutant is highly competitive in nodule occupancy compared with the wild-type strain. Sequence analysis of the mutant region revealed a new cluster of genes, termed the “ntrPR operon,” which is highly homologous to a group of vap-related genes of various pathogenic bacteria that are presumably implicated in bacterium-host interactions. On the basis of its favorable properties, the strain is a good candidate for future agricultural utilization.

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