Abstract
Plants take up the nitrogen necessary for their growth mainly in the form of nitrate. To cope with spatio-temporal fluctuations in NO3- availability in soils, these organisms have developed adaptation mechanisms specific to each situation. Plant N response involves several signaling pathways that depend on the N variation scenarios of the medium. Two major signaling pathways are studied in this thesis. The Primary Nitrate Response (or PNR) which corresponds to the rapid (within minutes) and nitrate-specific responses of the plant when provided with Nitrate. The Nitrogen Starvation response (or NSR) which corresponds to the slower response (within days) which makes it possible to overcome the lack of N in the medium. Although some molecular actors are known in each of the pathways (PNR and NSR); i) the NSR is significantly less well documented than the PNR, ii) nothing is known about the coordination of the 2 signaling pathways. During my thesis I was able to demonstrate that a subgroup of the GARP transcription factor family induced during PNR is directly involved in the regulation of NSR (repression of transport genes with a very high nitrate affinity). This provides both new NSR regulators and a coordination mechanism between the 2 signaling pathways. The phenotypes recorded for plants altered in this transcription factors family open up perspectives for crop biotechnological improvements because they have nitrate transport capacities far superior to wild plants.Results regarding the subcellular dual localization of HRS1 and the role of HRS1 in controlling the redox status of plants are presented and discussed in the context of the previously proposed PNR-NSR interaction model.