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Signal transduction involved in early steps of nodule formation in the rhizobium-legume symbiosis: an interdisciplinary approach


Bacteria of the genes Rhizobium and Bradyhizobium induce the formation of a new organ, the nodule, on the roots of legumes.
During early nodule development, a number of genes (early nodulin genes) are specifically expressed. Two such genesm ENOD5 and ENOD12 from pea are presently being characterized by the Wageningen group. A bacterial factor purified and characterized from Rhizobium meliloti by the Toulouse groups is capable of triggering the early events of nodule formation including the onset of early nodulin gene expression. Several DNA sequences and DNA binding proteins involved in the expression of late nodulin genes have been characterized by the Aarhus group using a legume transformation system. Bringing together the expertise of the three groups we propose a project focusing on a signal transduction pathway of early nodule development, starting from the recognition of the bacterial factor by the plant to the initiation of plant gene expression. In order to investigate the specificity of the bacterial factor, a number of different factors, either chemically modified or products of bacterial mutants, will be tested for their ability to initiate the developmental process leading to nodule formation. This part of the project also provides important knowledge for the identification of plant receptors recogniwing and responding to the bacterial factors. Based on the obtained DNA sequence information on the ENOD5 and ENOD12 genes a series of promoter/reporter gene constructs will be analysed by transient expression assay and in transgenic legumes. The DNA regulatory elements defined by this analysis will be subjected to a protein/DNA binding study, to define trans-acting factors involved in early nodulin expression. The interdepence of the trans-acting factors and the inducing bacterial factors will be analysed.


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Participants (3)

Centre National de la Recherche Scientifique (CNRS)
205 Route De Narbonne
31077 Toulouse
Landbouwuniversiteit Wageningen
6703 HA Wageningen
Århus Universitet
10,Gustav Wieds Vej 10
8000 Århus