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Regulatory networks that control gene expression in bacteroids of Rhizobium sp. NGR234

English title Regulatory networks that control gene expression in bacteroids of Rhizobium sp. NGR234
Applicant Perret Xavier
Number 116591
Funding scheme Project funding
Research institution Département de Biologie Végétale Faculté des Sciences Université de Genève
Institution of higher education University of Geneva - GE
Main discipline Molecular Biology
Start/End 01.05.2007 - 30.04.2013
Approved amount 260'000.00
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All Disciplines (2)

Discipline
Molecular Biology
Botany

Keywords (6)

symbiosis; transcription; nitrogen fixation; nodules; differentiation; global regulation

Lay Summary (English)

Lead
Lay summary
Biological nitrogen fixation can be performed by various prokaryotes including soil bacteria collectively called rhizobia, which form symbiotic associations with members of the plant family Leguminosae. These symbiotic associations lead to the formation on the stems and roots of host plants of specialised structures called nodules, where endosymbiotic rhizobia will differentiate into a nitrogen-fixing competent form known as bacteroids. In return for the ammonia fixed by bacteroids, host plants supply the microsymbionts with amino acids and photosynthates required to fuel the enzymatic reduction of nitrogen. Nodules also provide the low free-oxygen environment required to preserve the activity of the bacterial nitrogenase, the enzyme that reduces atmospheric dinitrogen.The intimate co-ordination of expression of the plant and bacterial genomes that is required for an efficient symbiotic nitrogen fixation is mostly mediated through the exchange of a series of molecular signals. At the onset of the association, flavonoids exuded by roots and Nod-factors (the rhizobial response to them) are key signals that contribute extensively to the specificity of Rhizobium-legumes symbioses. Within nodules, the expression of bacterial genes is principally regulated by oxygen, or rather the absence of it. In many rhizobia, a complex regulatory cascade that includes the two component system FixL-FixJ, the sigma 54 (RpoN) dependent transcriptional activator NifA as well as other regulatory proteins such as FixK, directs the transcription of nitrogen fixation genes (nif and fix).As a model microsymbiont, we selected Rhizobium species strain NGR234 that induces the formation of nodules on the roots of more than 120 genera of legumes, as well as the non-legume Parasponia andersonii. Since bacteroids of NGR234 reduce atmospheric nitrogen in nodules of either determinate (DT) or indeterminate (IDT) types, NGR234 is a model of choice to study the molecular basis for broad host-range symbiotic nitrogen fixation. Surprisingly, analysis of the genome sequence indicate that NGR234 lacks a conserved FixLJ regulatory system, and despite its extensive similarity with the genome of Sinorhizobium meliloti strain 1021, also conserved FixK activators. Thus, NGR234 evolved not only ways to induce the formation of nodules on many different hosts, it also implemented a transcriptional control of nif and fix genes that is distinct from other rhizobia and nevertheless sufficiently flexible for allowing nitrogen fixation in different nodule backgrounds. The aims of this research proposal are to dissect the regulatory networks that control gene expression inside bacteroids of NGR234, and understand how NGR234 responds to the environments found in the nodules of different hosts.
Direct link to Lay Summary Last update: 21.02.2013

Responsible applicant and co-applicants

Name Institute

Employees

Publications

Publication
In situ identification of plant-invasive bacteria with MALDI-TOF mass spectrometry
Ziegler Dominik, Mariotti Anna, Pflueger Valentin, Saad Maged, Vogel Guido, Tonolla Mauro, Perret Xavier (2012), In situ identification of plant-invasive bacteria with MALDI-TOF mass spectrometry, in PLOS ONE, 7(5), 1-7.
Functional analysis of the nifQdctA1y4vGHIJ operon of Sinorhizobium fredii strain NGR234 using a transposon with a NifA-dependent read-out promoter
Fumeaux Coralie, Bakkou Nadia, Kopcinska Joanna, Golinowski Wladyslav, Westenberg David J., Müller Peter, Perret Xavier (2011), Functional analysis of the nifQdctA1y4vGHIJ operon of Sinorhizobium fredii strain NGR234 using a transposon with a NifA-dependent read-out promoter, in Microbiology, 157, 2745-2758.
Rhizobium sp Strain NGR234 Possesses a Remarkable Number of Secretion Systems
Schmeisser Christel, Liesegang Heiko, Krysciak Dagmar, Bakkou Nadia, Le Quere Antoine, Wollherr Antje, Heinemeyer Isabelle, Morgenstern Burkhard, Pommerening-Roeser Andreas, Flores Margarita, Palacios Rafael, Brenner Sydney, Gottschalk Gerhard, Schmitz Ruth A., Broughton William J., Perret Xavier, Strittmatter Axel W., Streit Wolfgang R. (2009), Rhizobium sp Strain NGR234 Possesses a Remarkable Number of Secretion Systems, in APPLIED AND ENVIRONMENTAL MICROBIOLOGY, 75(12), 4035-4045.

Collaboration

Group / person Country
Types of collaboration
Philipps Universität Marburg Germany (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
Mabritec AG Switzerland (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
- Industry/business/other use-inspired collaboration

Scientific events

Active participation

Title Type of contribution Title of article or contribution Date Place Persons involved


Self-organised

Title Date Place
9th European Nitrogen Fixation Conference 06.09.2010 Genève, Suisse (CICG)

Associated projects

Number Title Start Funding scheme
146548 Towards a synthetic minimal replicon for symbiotic nitrogen fixation 01.04.2014 Project funding
146548 Towards a synthetic minimal replicon for symbiotic nitrogen fixation 01.04.2014 Project funding
67977 Global gene regulation in bacteroids of Rhizobium sp. NGR234 01.03.2003 Project funding
173191 Synthetic replicons to challenge legumes with single "nodulation keys" and monitor plant responses with phenotypic and transcriptome analyses 01.10.2017 Project funding

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