Integration of physiological and developmental responses of the plant to nitrate: role of the NRT1.1 (NPF6.3/CHL1)-dependent nitrate sensing pathway in determining Nitrogen Use Efficiency – NitraSense

Nitrogen is quantitatively the most important nutrient that plants acquire from the soil thanks to their roots. In many species, nitrate is the main source of nitrogen. However, nitrate concentration in the soil solution dramatically fluctuates in both time and space, which constitutes a major limitation to plant biomass production. Therefore, for optimizing the acquisition of this crucial resource, plants must constantly adapt to the changes in external nitrate availability by modifying their physiology and development. The NitraSense project aims at investigating the nitrate sensing and signaling mechanisms in Arabidopsis thaliana, allowing this plant to develop relevant adaptive responses to nitrate. The three French and Taiwanese partners have played a pivotal role in the elucidation of these mechanisms because they have independently identified more than ten different molecular regulators (genes/proteins) putatively participating in the same sensing/signaling system controlled by the nitrate sensor NRT1.1/NPF6.3. These regulators trigger a wide range of both physiological and developmental responses to changes in nitrate availability. The objective of the NitraSense partners is now to combine their expertise and tools to unravel the structure and functioning of the network gathering these regulators, to validate the postulated central role of NRT1.1/NPF6.3 in governing the network, and to understand how this network coordinates physiological and developmental mechanisms to yield an integrated response of the whole plant. We will aim at determining how the expression of the regulators is controlled on transcriptional and post-transcriptional level and how these regulators interact with each other, physically or functionally, to activate specific ‘branches’ of the network in response to various N treatments (first supply of nitrate, ample or suboptimal supply of nitrate, nitrate starvation, etc…). The functional role of the various network ‘branches’ will be investigated through a reverse genetics approach (single and multiple mutants) in order to identify the different responses they specifically trigger in the different organs/tissues (up-regulation of nitrate uptake systems, changes in metabolism, modulation of root development, etc…). The overall significance of the regulatory network on nitrogen use efficiency will be assessed to determine its potential interest in breeding strategies for more nitrogen-efficient crops. Hence, the genotypes with mutations or combinations of mutations impacting the various physiological/developmental responses to nitrate will be grown on soil in pots, and subjected to high-throughput phenotyping of nitrate use efficiency on a dedicated automated platform.