The objectives of this proposal are to get an integrated view i) of the regulator networks operating in legumes and rhizobia leading to their symbiotic association and to symbiotic nitrogen fixation and ii) of the metabolic interactions implicated in nitrogen fixation. Studies directed towards these objectives will be performed on two grain legumes, faba bean and french bean, and one forage legume, alfalfa, and on their respective nodulating rhizobia. For reasons of application of the results obtained, two industrial partners will participate in the project.
l.We will characterize and compare the expression pattern, inside the nodule and inside source tissues, of genes which encode diagnostic enzyme components of the major metabolic routes relevant for the process of nitrogen fixation: among these are the plant ADP-glucose pyrophosphorylase, the chloroplastidic fructose-1,6bisphosphatase, and the triose-phosphate translocator which are involved in the carbon flux to the nodules; plant sucrose synthase and carbonic anhydrase involved in the plant carbon metabolism in nodule tissues, the bacterial dicarboxylic acid permease which is involved in the uptake of carbon compounds by the microsymbiont, and the plant glutamine synthetase which participates in the assimilation of fixed nitrogen.
2.Recording the effects of modulating the individual expression of some of these genes of both plant and bacterial origin on the efficiency of nitrogen fixation in various environmental conditions, will give information on the implication of th; encoded enzymes and the corresponding metabolic pathways on the overall balance of the nitrogen fixation process and/or its flexibility towards environmental variations. We will use highly defined environmental conditions, e.g. in growth chambers and in addition non-artificial conditions, e.g. in field trials, to get an integrated view under conditions suitable for application. Evaluations on the expression of bacterial or plant genes in engineered symbiotic associations will give information on the physiological integration of the system and indications or possible regulatory signals.
3.We will attempt to further characterize these regulatory signals: metabolic signals will be looked for by expression studies in cell cultures or by transient expression in protoplasts. Identification and comparison of regulatory secIuences in the upstream regions of the genes will also be exploited in a search for developmental signals, specifically in case where expression patterns of several genes would be identical.
4.Regulation of the expression of bacterial genes, either directly involved in nitrogen fixation or indicative of the differentiation of endosymbiotic bacteria, will be studied as part of the carbon as well as the nitrogen regulatory and metabolic network of the nodule and as a means to identify the regulatory signals.
Funding SchemeCSC - Cost-sharing contracts
91190 Gif Sur Yvette