Dataset Information

How legumes control nitrogen fixation by root nodule bacteria

ABSTRACT: Rhizobia are soil bacteria that can enter into complex symbiotic relationships with legumes, where rhizobia induce the formation of nodules on the plant root. Inside nodules, rhizobia differentiate into nitrogen-fixing bacteroids that reduce atmospheric nitrogen into ammonia, secreting it to the plant host in exchange for carbon. During the transition from free-living bacteria to bacteroids, rhizobial metabolism undergoes major changes. To investigate the metabolism of bacteroids and contrast it with the free-living state, we quantified the proteome of unlabelled bacteroids relative to 15N-labelled free-living rhizobia. The data were used to build a core metabolic model of pea bacteroids for the strain Rhizobium leguminosarum bv. viciae 3841.

INSTRUMENT(S): LTQ Orbitrap

ORGANISM(S): Rhizobium Leguminosarum Bv. Viciae 3841

TISSUE(S): Bacteroid

SUBMITTER: Gerhard Saalbach

LAB HEAD: Philip Poole

PROVIDER: PXD019467 | Pride | 2021-09-09

REPOSITORIES: Pride

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Metabolic control of nitrogen fixation in rhizobium-legume symbioses.

Schulte Carolin C M CCM Borah Khushboo K Wheatley Rachel M RM Terpolilli Jason J JJ Saalbach Gerhard G Crang Nick N de Groot Daan H DH Ratcliffe R George RG Kruger Nicholas J NJ Papachristodoulou Antonis A Poole Philip S PS

Science advances 20210730 31

Rhizobia induce nodule formation on legume roots and differentiate into bacteroids, which catabolize plant-derived dicarboxylates to reduce atmospheric N<sub>2</sub> into ammonia. Despite the agricultural importance of this symbiosis, the mechanisms that govern carbon and nitrogen allocation in bacteroids and promote ammonia secretion to the plant are largely unknown. Using a metabolic model derived from genome-scale datasets, we show that carbon polymer synthesis and alanine secretion by bacter ...[more]

PMID: 34330708

Similar Datasets

Project description:During the legume-rhizobium symbiosis, free-living soil bacteria known as rhizobia trigger the formation of root nodules. The rhizobia infect these organs and adopt an intracellular lifestyle within the symbiotic nodule cells where they become nitrogen-fixing bacteroids. Several legume lineages enforce their symbionts into an extreme cellular differentiation, comprising cell enlargement and genome endoreduplication. The antimicrobial peptide transporter BclA is a major determinant of this differentiation process in Bradyrhizobium sp. ORS285, a symbiont of Aeschynomene spp.. In the absence of BclA, Bradyrhizobium sp. ORS285 proceeds until the intracellular infection of nodule cells but the bacteria cannot differentiate into enlarged polyploid bacteroids and fix nitrogen. The nodule bacteria of the bclA mutant constitute thus an intermediate stage between the free-living soil bacteria and the intracellular nitrogen-fixing bacteroids. Metabolomics on whole nodules of Aeschynomene afraspera and Aeschynomene indica infected with the ORS285 wild type or the bclA mutant revealed 47 metabolites that differentially accumulated concomitantly with bacteroid differentiation. Bacterial transcriptome analysis of these nodules discriminated nodule-induced genes that are specific to differentiated and nitrogen-fixing bacteroids and others that are activated in the host microenvironment irrespective of bacterial differentiation and nitrogen fixation. These analyses demonstrated that the intracellular settling of the rhizobia in the symbiotic nodule cells is accompanied with a first transcriptome switch involving several hundreds of upregulated and downregulated genes and a second switch accompanying the bacteroid differentiation, involving less genes but that are expressed to extremely elevated levels. The transcriptomes further highlighted the dynamics of oxygen and redox regulation of gene expression during nodule formation and we discovered that bclA represses the expression of non-ribosomal peptide synthetase gene clusters suggesting a non-symbiotic function of BclA. Together, our data uncover the metabolic and gene expression changes that accompany the transition from intracellular bacteria into differentiated nitrogen-fixing bacteroids.

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