An INRA research team in Montpellier, working in collaboration with teams from CNRS in Strasbourg and New York University, have recently achieved a major advance in our understanding of plant nutrition. They have characterized a gene involved in a molecular mechanism that can adjust the uptake of soil nitrogen by roots as a function of the nitrogen requirements of the whole plant. This research may facilitate the selection of varieties displaying a more efficient use of nitrate fertilisers, so as to ensure more environmentally-friendly crops.

To ensure their nutrition, plants absorb soil nitrate, or NO3- (the principal source of nitrogen for herbaceous plants) via their roots. This phenomenon is rendered possible by highly efficient transporters that allow the passage of nitrate through the membranes of cells at the periphery of the root. However, because soil nitrate availability is heterogeneous and can fluctuate over time and in space, plants must constantly modulate their absorption capacity so as to maintain a sufficient nitrate intake that will meet their needs. This is facilitated by a mechanism qualified as "satiety" (by analogy with animals), that allows the plant to reduce its absorption when its nitrogen requirements have been fulfilled.

For the first time, researchers in Montpellier have identified a gene (HNI9/IWS1) that participates in this mechanism in the model plant Arabidopsis thaliana. This gene codes for a nuclear protein in plant cells, the function of which had been very poorly understood until now. The scientists have shown that when the plant is satiated, this protein causes the deposit of epigenetic markers in the gene of the principal membrane transporter of root NO3. These markers do not modify the gene sequence but act as a "modulator" of its expression that represses synthesis of the transporter. The quantity of the transporter thus diminishes, and root nitrogen absorption is consequently reduced.

This original research opens perspectives to improve the use of fertilisers in agriculture. Indeed, nitrate is one of the principal ingredients in these fertilizers, and that part which is not taken up by crops can pollute ground and surface water. In this context, the discovery of mechanisms that are naturally implemented by plants to adjust nitrate uptake to their nutritional requirements, is of importance. One of the long-term prospects is to render plants capable of accumulating nitrogen even when their immediate nutritional requirements are met, so that they can remobilise it at a later stage. This could improve soil nitrate use efficiency by plants and allow a reduction in fertilizer inputs in agriculture.