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Transcriptomic analysis of Rhizobium leguminosarum biovar viciae in symbiosis with host plants Pisum sativum and Vicia cracca.

ABSTRACT: Rhizobium leguminosarum bv. viciae forms nitrogen-fixing nodules on several legumes, including pea (Pisum sativum) and vetch (Vicia cracca), and has been widely used as a model to study nodule biochemistry. To understand the complex biochemical and developmental changes undergone by R. leguminosarum bv. viciae during bacteroid development, microarray experiments were first performed with cultured bacteria grown on a variety of carbon substrates (glucose, pyruvate, succinate, inositol, acetate, and acetoacetate) and then compared to bacteroids. Bacteroid metabolism is essentially that of dicarboxylate-grown cells (i.e., induction of dicarboxylate transport, gluconeogenesis and alanine synthesis, and repression of sugar utilization). The decarboxylating arm of the tricarboxylic acid cycle is highly induced, as is gamma-aminobutyrate metabolism, particularly in bacteroids from early (7-day) nodules. To investigate bacteroid development, gene expression in bacteroids was analyzed at 7, 15, and 21 days postinoculation of peas. This revealed that bacterial rRNA isolated from pea, but not vetch, is extensively processed in mature bacteroids. In early development (7 days), there were large changes in the expression of regulators, exported and cell surface molecules, multidrug exporters, and heat and cold shock proteins. fix genes were induced early but continued to increase in mature bacteroids, while nif genes were induced strongly in older bacteroids. Mutation of 37 genes that were strongly upregulated in mature bacteroids revealed that none were essential for nitrogen fixation. However, screening of 3,072 mini-Tn5 mutants on peas revealed previously uncharacterized genes essential for nitrogen fixation. These encoded a potential magnesium transporter, an AAA domain protein, and proteins involved in cytochrome synthesis.

SUBMITTER: Karunakaran R

PROVIDER: S-EPMC2698398 | biostudies-literature | 2009 Jun

REPOSITORIES: biostudies-literature

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Transcriptomic analysis of Rhizobium leguminosarum biovar viciae in symbiosis with host plants Pisum sativum and Vicia cracca.

Karunakaran R R Ramachandran V K VK Seaman J C JC East A K AK Mouhsine B B Mauchline T H TH Prell J J Skeffington A A Poole P S PS

Journal of bacteriology 20090417 12

Rhizobium leguminosarum bv. viciae forms nitrogen-fixing nodules on several legumes, including pea (Pisum sativum) and vetch (Vicia cracca), and has been widely used as a model to study nodule biochemistry. To understand the complex biochemical and developmental changes undergone by R. leguminosarum bv. viciae during bacteroid development, microarray experiments were first performed with cultured bacteria grown on a variety of carbon substrates (glucose, pyruvate, succinate, inositol, acetate, a ...[more]

PMID: 19376875

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Project description:Rhizobium leguminosarum bv. viciae UPM791 contains a second copy of the fnrN gene, which encodes a redox-sensitive transcriptional activator functionally homologous to Escherichia coli Fnr. This second copy (fnrN2) is located in the symbiotic plasmid, while fnrN1 is in the chromosome. Isolation and sequencing of the fnrN2 gene revealed that the deduced amino acid sequence of FnrN2 is 87.5% identical to the sequence of FnrN1, including a conserved cysteine-rich motif characteristic of Fnr-like proteins. Individual R. leguminosarum fnrN1 and fnrN2 mutants exhibited a Fix+ phenotype and near wild-type levels of nitrogenase and hydrogenase activities in pea (Pisum sativum L.) nodules. In contrast, an fnrN1 fnrN2 double mutant formed ineffective nodules lacking both nitrogenase and hydrogenase activities. Unlike the wild-type strain and single fnrN1 or fnrN2 mutants, the fnrN1 fnrN2 double mutant was unable to induce micro-oxic or bacteroid activation of the hypBFCDEX operon, which encodes proteins essential for hydrogenase synthesis. In the search for symbiotic genes that could be controlled by FnrN, a fixNOQP operon, putatively encoding a micro-oxically induced, bacteroid-specific cbb3-type terminal cytochrome oxidase, was isolated from strain UPM791 and partially sequenced. The fixNOQP operon was present in a single copy located in the symbiotic plasmid, and an anaerobox was identified in the fixN promoter region. Consistent with this, a fixNOQP'-lacZ fusion was shown to be highly induced in micro-oxic cells of the wild-type strain. A high level of micro-oxic induction was also observed in single fnrN1 and fnrN2 mutants, but no detectable induction was observed in the fnrN1 fnrN2 double mutant. The lack of expression of fixNOQP in the fnrN1 fnrN2 double mutant is likely to cause the observed Fix- phenotype. These data demonstrate that, contrary to the situation in other rhizobia, FnrN controls both hydrogenase and nitrogenase activities of R. leguminosarum bv. viciae UPM791 in the nodule and suggest that this strain lacks a functional fixK gene.

Dataset Information

Transcriptomic analysis of Rhizobium leguminosarum biovar viciae in symbiosis with host plants Pisum sativum and Vicia cracca.

Publications

Transcriptomic analysis of Rhizobium leguminosarum biovar viciae in symbiosis with host plants Pisum sativum and Vicia cracca.

Similar Datasets

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