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General stress response of Bradyrhizobium diazoefficiens: signals, signal transduction pathways and effectors involved in symbiosis

English title General stress response Bradyrhizobium diazoefficiens: signals, signal transduction pathways and effectors involved in symbiosis
Applicant Fischer Hans-Martin
Number 173255
Funding scheme Project funding (Div. I-III)
Research institution Institut für Mikrobiologie Departement Biologie ETH Zürich
Institution of higher education ETH Zurich - ETHZ
Main discipline Experimental Microbiology
Start/End 01.04.2017 - 31.08.2020
Approved amount 515'054.00
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All Disciplines (2)

Discipline
Experimental Microbiology
Botany

Keywords (10)

Bradyrhizobium japonicum; plant-microbe interaction; signal transduction; nitrogen fixation; general stress response; gene regulation ; Bradyrhizobium diazoefficiens; ECF sigma factor; symbiosis; root nodules

Lay Summary (German)

Lead
Die symbiotische Interaktion von (Brady)Rhizobium Bakterien mit Pflanzen aus der Familie der Leguminosen führt zur Entstehung von Wurzelknöllchen, in welchen die endosymbiontischen Bakterien atmosphärischen Stickstoff zu Ammonium reduzieren und diesen der Wirtspflanze als Stickstoff-Quelle zur Verfügung stellen. Das vorliegende Projekt leistet einen Beitrag zum besseren Verständnis der molekularen Faktoren und Prozesse, welche an der Schnittstelle zwischen Bradyrhizobium diazoefficiens und dessen Wirtspflanzen (z.B. Sojabohne) benötigt werden, um eine funktionelle Symbiose auszubilden.
Lay summary

Allgemeine Stressantwort von Bradyrhizobium diazoefficiens: Symbiose-relevante Signale, Signal-Transduktionswege und Effektoren

Système de réponse générale aux stress chez Bradyrhizobium diazoefficiens: signaux, voies de signalisation and effecteurs impliqués dans la symbiose

General stress response of Bradyrhizobium diazoefficiens: signals, signal transduction pathways and effectors involved in symbiosis 

Inhalt und Ziele

Die Ausbildung der Symbiose ist ein komplexer Prozess, dem ein chemischer Dialog zwischen den Symbiosepartnern zugrunde liegt. Eine erfolgreiche Interaktion der Symbiosepartner zu einer kontrollierten Infektion und Besiedlung von Pflanzenzellen durch die bakteriellen Symbionten. Ein bakterieller Transkriptionsfaktor (σEcfG), der in freilebenden B. diazoefficiens Zellen die allgemeine Stressantwort reguliert, wird in einem sehr frühen Symbiose-Stadium auch für die normale Wurzelknöllchen-Entwicklung benötigt. In diesem Projekte wird untersucht, welche Signale unter Symbiose-Bedingungen die Stressantwort auslösen, wie diese vom Symbionten detektiert, weitergeleitet und zu physiologischen Reaktionen führen, die für den Infektionsprozess wichtig sind. Dazu gehört u.a. die erhöhte Synthese eines Disaccharids, dessen Funktion in der Symbiose untersucht wird.

Relevanz

Das Projekt befasst mit Grundlagenforschung und stellt einen Beitrag dar zum besseren molekularen Verständnis von Bakterien-Pflanzen Interaktionen. Insbesondere könnten dabei neue Faktoren und Prozesse identifiziert werden, welche zur Ausbildung einer effizienten Symbiose nötig sind. Diese Erkenntnisse können auch einen Beitrag leisten zum Verständnis der Interaktionen von pathogen Mikroorganismen mit eukaryotischen Wirtszellen, weil sich darunter Bakterien befinden, die zur gleichen Gruppe wie die Rhizobien gehören und von denen bekannt ist, dass eine funktionelle allgemeine Stressantwort für eine chronische Infektion wichtig ist.

Direct link to Lay Summary Last update: 12.04.2017

Responsible applicant and co-applicants

Employees

Project partner

Publications

Publication
An Integrated Systems Approach Unveils New Aspects of Microoxia-Mediated Regulation in Bradyrhizobium diazoefficiens
Fernández Noemí, Cabrera Juan J., Varadarajan Adithi R., Lutz Stefanie, Ledermann Raphael, Roschitzki Bernd, Eberl Leo, Bedmar Eulogio J., Fischer Hans-Martin, Pessi Gabriella, Ahrens Christian H., Mesa Socorro (2019), An Integrated Systems Approach Unveils New Aspects of Microoxia-Mediated Regulation in Bradyrhizobium diazoefficiens, in Frontiers in Microbiology, 10, 924.
A functional general stress response of Bradyrhzobium diazoefficiens is required for early stages of host plant infection
Ledermann Ra, Bartsch Il, Müller Ba, Wülser Janine, Fischer Hans-Martin (2018), A functional general stress response of Bradyrhzobium diazoefficiens is required for early stages of host plant infection, in Molecular Plant-Microbe Interactions, 31(5), 537-547.

Collaboration

Group / person Country
Types of collaboration
Prof. N. Zamboni, ETH Zurich Switzerland (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Research Infrastructure
Prof. J.A. Vorholt & Dr. P. Kiefer, ETH Zurich Switzerland (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Research Infrastructure

Scientific events

Active participation

Title Type of contribution Title of article or contribution Date Place Persons involved
18th Molecular Plant-Microbe Interactions Congress Poster Activation of the general stress response by stress-specific sensor histidine kinases is crucial for host infection by Bradyrhizobium diazoefficiens 14.07.2019 Glasgow, Great Britain and Northern Ireland Fischer Hans-Martin; Ledermann Raphael; Wülser Janine;
How microorganisms view their world Poster Function and regulation of ECF σ factor σEcfG in the nitrogen-fixing soybean symbiont Bradyrhizobium diazoefficiens 23.09.2018 Marburg, Germany Ledermann Raphael; Fischer Hans-Martin; Wülser Janine;
How microorganisms view their world Talk given at a conference Function and regulation of the ECF σ factor σEcfG in thenitrogen-fixing soybean symbiont Bradyrhizobium diazoefficiens 23.09.2018 Marburg, Germany Wülser Janine; Ledermann Raphael; Fischer Hans-Martin;
13th European Nitrogen Fixation Conference Poster Role of general stress response-controlled trehalose biosynthesis in the Bradyrhizobium diazoefficiens - soybean symbiosis 18.08.2018 Stockholm, Sweden Ledermann Raphael; Fischer Hans-Martin;
13th European Nitrogen Fixation Conference Poster The symbiosis-relevant subset of general stress response-activating kinases in Bradyrhizobium diazoefficiens 18.08.2018 Stockholm, Sweden Fischer Hans-Martin; Wülser Janine; Ledermann Raphael;
Bacterial networks (BacNet17) Poster The role of the general stress response in the Bradyrhizobium diazoefficiens - legume symbiosis 09.09.2017 Sant Feliu de Guixols, Spain Ledermann Raphael; Wülser Janine; Fischer Hans-Martin;
20th International Conference on Nitrogen Fixation Poster General stress response of Bradyrhizobium diazoefficiens: Control of PhyR activity by stress-specific kinases 03.09.2017 Granada, Spain Ledermann Raphael; Fischer Hans-Martin; Wülser Janine;
20th International Conference on Nitrogen Fixation Talk given at a conference The role of the general stress response in the Bradyrhizobium diazoefficiens - legume symbiosis 03.09.2017 Granada, Spain Wülser Janine; Ledermann Raphael; Fischer Hans-Martin;
20th International Conference on Nitrogen Fixation Poster Novel expression tools reveal crucial spatio-temporal control of trehalose biosynthesis in the Bradyrhizobium diazoefficiens - soybean symbiosis 03.09.2017 Granada, Spain Ledermann Raphael; Fischer Hans-Martin;


Awards

Title Year
ETH Medal for outstanding doctoral theses 2018

Associated projects

Number Title Start Funding scheme
153446 The role of Bradyrhizobium japonicum extracytoplasmic function (ECF) sigma factor EcfG in formation of an effective symbiosis 01.04.2014 Project funding (Div. I-III)
153446 The role of Bradyrhizobium japonicum extracytoplasmic function (ECF) sigma factor EcfG in formation of an effective symbiosis 01.04.2014 Project funding (Div. I-III)
183901 Metabolic bottlenecks in rhizobia affecting competitive nodulation during infection stages 01.03.2019 Postdoc.Mobility

Abstract

Rhizobia including Bradyrhizobium diazoefficiens are Gram-negative Alphaproteobacteria that are capable of symbiotic nitrogen fixation in specialized nodules formed by their legume host plants in response to the mutual exchange of chemical signals. During transition from the free-living state in soil to the endosymbiotic state rhizobia must cope with a latent host defense reaction that is manifested at early stages of the infection process. At a later stage, when nitrogen-fixing bacteroids live as true endosymbionts in plant cells they need to adapt their physiology as they entirely depend on nutrients provided by the host. In both symbiotic partners, complex regulatory networks are involved in the control of symbiotic genes to ensure coordinated development and persistent integrity of functional nodules. Among the rhizobial regulators are s factor proteins which, in association with RNA polymerase core enzyme, enable transcription from specific promoters. One of them, sEcfG, together with its anti- s factor NepR and the anti-anti-s factor PhyR forms the core element in the regulation of the general stress response (GSR) in B. diazoefficiens as in many other Alphaproteobacteria. In our previous work, we have shown that a functional GSR not only is required for stress tolerance under free-living conditions but, unlike in other rhizobia, also for a balanced interaction with host plants. Nodules induced by a B. diazoefficiens mutant lacking sEcfG appear delayed and most of them are aberrant, indicating that sEcfG is needed for normal nodule organogenesis and persistence. More recently we have shown that sEcfG-dependent functions are required at a very early infection stage, and a mutant deleted for the sEcfG-controlled trehalose biosynthesis gene otsA phenocopies a sEcfG mutant. While this indicates that trehalose biosynthesis is crucial for early steps in the symbiotic interaction of B. diazoefficiens with hosts, the underlying details are not understood to date. In project A of this proposal we will address the role of trehalose during the infection process and later stages of the symbiosis by testing if other compatible solutes can functionally replace trehalose. This question is particularly attractive in the light of recent findings that point to a role of trehalose (synthesis) in pathogenic bacteria-plant interactions and regulation of plant developmental processes. Project B is focusing on the signaling network upstream of the PhyR-NepR-sEcfG regulatoty core. In B. diazoefficiens, 11 distinct candidate sensory kinases are present which may sense different stress signals to activate a stress response via phosphorylation of PhyR. Mutants lacking individual or multiple kinases will be constructed and their free-living stress responsiveness and symbiotic phenotype will be determined. Special attention will be given to the sensory kinase(s) which perceive a postulated, unidentified "symbiotic stress signal" that triggers GSR induction during the onset of symbiosis. Taken together, we will characterize the input and output level of the B. diazoefficiens GSR to better understand its critical role in the interaction of this bacterium with host plants.
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