Insertion of Transposon Tn5tac1 in the Sinorhizobium meliloti Malate Dehydrogenase (mdh) Gene Results in Conditional Polar Effects on Downstream TCA Cycle Genes

Dymov, Sergiy; Meek, David J. J.; Steven, Blaire; Driscoll, Brian T.

doi:10.1094/mpmi.2004.17.12.1318

Cited by 24 publications

(15 citation statements)

References 73 publications

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“…Interestingly, in the icd background, spontaneous mutants lacking citrate synthase activity appeared (25). Similar viable phenotypes have been obtained for other enzymes involved in the TCA cycle, such as 2-oxoglutarate dehydrogenase and succinate dehydrogenase, as well as malic enzymes (8)(9)(10)(11)14).…”

supporting

confidence: 62%

Deletion of Citrate Synthase Restores Growth of Sinorhizobium meliloti 1021 Aconitase Mutants

et al. 2009

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The symbiotic nitrogen-fixing bacterium Sinorhizobium meliloti 1021 encodes only one predicted aconitase (AcnA) in its genome. AcnA has a significant degree of similarity with other bacterial aconitases that behave as dual proteins: enzymes and posttranscriptional regulators of gene expression. Similar to the case with these bacterial aconitases, AcnA activity was reversibly labile and was regained upon reconstitution with reduced iron. The aconitase promoter was active in root nodules. acnA mutants grew very poorly, had secondary mutations, and were quickly outgrown by pseudorevertants. The acnA gene was stably interrupted in a citrate synthase (gltA) null background, indicating that the intracellular accumulation of citrate may be deleterious for survival of strain 1021. No aconitase activity was detected in this mutant, suggesting that the acnA gene encodes the only functional aconitase of strain 1021. To uncover a function of AcnA beyond its catalytic role in the tricarboxylic acid cycle pathway, the gltA acnA double mutant was compared with the gltA single mutant for differences in motility, resistance to oxidative stress, nodulation, and growth on different substrates. However, no differences in any of these characteristics were found.Aconitases (EC 4.2.1.3) are key enzymes in the tricarboxylic acid (TCA) cycle in both prokaryotes and eukaryotes, catalyzing the reversible isomerization of citrate into isocitrate via the intermediate cis-aconitate. The active site contains a [4Fe-4S] cluster that is required for enzymatic activity.

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confidence: 62%

Deletion of Citrate Synthase Restores Growth of Sinorhizobium meliloti 1021 Aconitase Mutants

et al. 2009

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“…The TCA cycle appears to be essential for nitrogen fixation in many rhizobia, including R. leguminosarum, S. meliloti, and Bradyrhizobium sp. ORS278, based on mutation of TCA-cycle enzymes leading to a Fix − phenotype (13,37,159). However, several mutations of isocitrate dehydrogenase, aconitase, or a component of the 2-ketoglutarate dehydrogenase complex are Fix + in B. japonicum USDA110 (50,129,143; reviewed in 141).…”

Section: Bacterial Carbon Metabolismmentioning

confidence: 99%

Transport and Metabolism in Legume-Rhizobia Symbioses

Udvardi

Poole²

2013

Annu. Rev. Plant Biol.

715

555

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Symbiotic nitrogen fixation by rhizobia in legume root nodules injects approximately 40 million tonnes of nitrogen into agricultural systems each year. In exchange for reduced nitrogen from the bacteria, the plant provides rhizobia with reduced carbon and all the essential nutrients required for bacterial metabolism. Symbiotic nitrogen fixation requires exquisite integration of plant and bacterial metabolism. Central to this integration are transporters of both the plant and the rhizobia, which transfer elements and compounds across various plant membranes and the two bacterial membranes. Here we review current knowledge of legume and rhizobial transport and metabolism as they relate to symbiotic nitrogen fixation. Although all legume-rhizobia symbioses have many metabolic features in common, there are also interesting differences between them, which show that evolution has solved metabolic problems in different ways to achieve effective symbiosis in different systems.

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“…Since the plants are cultured on nitrogen-free medium, they can grow only if reduced nitrogen is supplied by bacteroids within the nodule. Thus, the dry weight of the infected plant can be used as an indirect measure of nitrogen fixation (18,40). We measured the dry weight of plants inoculated with either wild-type, nodPQ, or cysH M. loti cells.…”

Section: Fig 4 Paps Biosynthesis Inmentioning

confidence: 99%

Mesorhizobium lotiProducesnodPQ-Dependent Sulfated Cell Surface Polysaccharides

2006

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Leguminous plants and bacteria from the family Rhizobiaceae form a symbiotic relationship, which culminates in novel plant structures called root nodules. The indeterminate symbiosis that forms between Sinorhizobium meliloti and alfalfa requires biosynthesis of Nod factor, a ␤-1,4-linked lipochitooligosaccharide that contains an essential 6-O-sulfate modification. S. meliloti also produces sulfated cell surface polysaccharides, such as lipopolysaccharide (LPS). The physiological function of sulfated cell surface polysaccharides is unclear, although mutants of S. meliloti with reduced LPS sulfation exhibit symbiotic abnormalities. Using a bioinformatic approach, we identified a homolog of the S. meliloti carbohydrate sulfotransferase, LpsS, in Mesorhizobium loti. M. loti participates in a determinate symbiosis with the legume Lotus japonicus. We showed that M. loti produces sulfated forms of LPS and capsular polysaccharide (KPS). To investigate the physiological function of sulfated polysaccharides in M. loti, we identified and disabled an M. loti homolog of the sulfate-activating genes, nodPQ, which resulted in undetectable amounts of sulfated cell surface polysaccharides and a cysteine auxotrophy. We concomitantly disabled an M. loti cysH homolog, which disrupted cysteine biosynthesis without reducing cell surface polysaccharide sulfation. Our experiments demonstrated that the nodPQ mutant, but not the cysH mutant, showed an altered KPS structure and a diminished ability to elicit nodules on its host legume, Lotus japonicus. Interestingly, the nodPQ mutant also exhibited a more rapid growth rate and appeared to outcompete wild-type M. loti for nodule colonization. These results suggest that sulfated cell surface polysaccharides are required for optimum nodule formation but limit growth rate and nodule colonization in M. loti.Most soils are limited in reduced forms of nitrogen. Thus, plants undergo symbioses with microorganisms that provide the plants with reduced nitrogen. The best studied of these symbioses occur between leguminous plants and a family of gram-negative bacteria known as rhizobia. The symbiosis culminates in the formation of novel structures on the plant root called nodules. To enter and colonize the nodules, the bacteria elicit a series of morphological changes in specialized epidermal cells called root hairs. The bacteria induce curling of the root hairs, trapping bacterial microcolonies in the center of the structure. The bacteria then elicit the formation of a plantderived tubular structure that emanates from the center of the curl, extending through the root hair and ultimately penetrating through the epidermis into the cortical layers of the root. This structure, known as an infection thread, is occupied by the bacteria and allows their entry into the interior of the root. The bacteria are released from the infection thread into the cytoplasm of plant cells within the nodule, where they differentiate into intracellular forms called bacteroids, which then reduce molecular dinitrogen for use...

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Insertion of Transposon Tn5tac1 in the Sinorhizobium meliloti Malate Dehydrogenase (mdh) Gene Results in Conditional Polar Effects on Downstream TCA Cycle Genes

Cited by 24 publications

References 73 publications

Deletion of Citrate Synthase Restores Growth of Sinorhizobium meliloti 1021 Aconitase Mutants

Deletion of Citrate Synthase Restores Growth of Sinorhizobium meliloti 1021 Aconitase Mutants

Transport and Metabolism in Legume-Rhizobia Symbioses

Mesorhizobium lotiProducesnodPQ-Dependent Sulfated Cell Surface Polysaccharides

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