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Rhizobium-plant symbioses require the precise timing and recognition of rhizobial secondary symbiotic signals

English title Rhizobium-plant symbioses require the precise timing and recognition of rhizobial secondary symbiotic signals
Applicant Broughton William John
Number 116858
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 Biochemistry
Start/End 01.05.2007 - 30.04.2010
Approved amount 377'000.00
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All Disciplines (4)

Experimental Microbiology
Molecular Biology

Keywords (6)

molecular plant-microbe interactions; protein secretion; plant defence responses; signal transduction; nitrogen fixation; lotus japonicus

Lay Summary (English)

Lay summary
Soil bacteria, collectively called rhizobia colonise members of the legume family of plants (Leguminosae) forming new organs (nodules) on the roots, in which the rhizobia associate symbiotically with the plant. In the nodules, rhizobia reduce atmospheric nitrogen to ammonia, which the plants can assimilate to promote growth. In return, the rhizobia are provided with photosynthetic products (carbohydrates) from the plant. For these reasons, rhizobia are widely used in agriculture to reduce the need for fertilisation. The range of partners that both the rhizobia and a particular legume can interact with is highly variable, as the symbiotic interaction is precisely controlled by the exchange of molecular signals between the bacterium and plant. We study a Rhizobium species named NGR234, which has an exceptionally large legume host range. We are particularly interested in the signalling molecules produced by NGR234, and the responses they provoke from the plant that allow these multiple symbiotic interactions to develop. Our previous work with NGR234 has uncovered the main players in terms of symbiotic signalling molecules, Nod-factors, Surface Polysaccharides and proteins secreted by a type III secretion system (T3SS). We have characterised these signal molecules structurally and genetically, as well as their regulation. What is now required is to determine how and where in planta these signals act, the location within the root during the infection process and the plant responses they provoke. Unfortunately rhizobia do not initiate a symbiosis with the model plant Arabidopsis thaliana, which has led to the development of alternative model plants, Lotus and Medicago, as well as the emerging model Phaseolus (common bean), with which the symbiotic process can be studied. NGR234 is known to nodulate Lotus, implying that the NGR234 signals produced are recognised and acted upon. Thus we will use the resources available for Lotus, to investigate the macro-effects on nodule formation and the micro-effects within the plant cells to uncover how rhizobial signals influence plant development. We are particularly interested to investigate any parallels between symbiotic signals and those used by plant pathogens to down regulate defence processes and allow bacterial entry into plant cells. At the same time, we will continue our work on other legumes within the host range of NGR234 to study the positive and negative effects of the symbiotic signals to see if the process is universal or customised for each plant. In this way we hope to use the results obtained from the model legume and apply them to more cultivated species, such as the common bean - an important food crop, to uncover ways to improve nitrogen fixation and thus cultivation.
Direct link to Lay Summary Last update: 21.02.2013

Responsible applicant and co-applicants


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Associated projects

Number Title Start Funding scheme
104097 Fine Tuning of Nodulation by Complementary Rhizobial Signals 01.05.2004 Project funding