Developmental and physiological responses of Brachypodium distachyon to fluctuating nitrogen availability.

The Nitrogen Use Efficiency (NUE) of grain cereals depends on nitrate (NO) uptake from the soil, translocation to the aerial parts, nitrogen (N) assimilation and remobilization to the grains. Brachypodium distachyon has been proposed as a model species to identify the molecular players and mechanisms that affects these processes, for the improvement of temperate C3 cereals. We report on the developmental, physiological and grain-characteristic responses of the Bd21-3 accession of Brachypodium to variations in NO availability. As previously described in wheat and barley, we show that vegetative growth, shoot/root ratio, tiller formation, spike development, tissue NO and N contents, grain number per plant, grain yield and grain N content are sensitive to pre- and/or post-anthesis NO supply. We subsequently described constitutive and NO-inducible components of both High and Low Affinity Transport Systems (HATS and LATS) for root NO uptake, and BdNRT2/3 candidate genes potentially involved in the HATS. Taken together, our data validate Brachypodium Bd21-3 as a model to decipher cereal N nutrition. Apparent specificities such as high grain N content, strong post-anthesis NO uptake and efficient constitutive HATS, further identify Brachypodium as a direct source of knowledge for crop improvement.