Developmental and physiological responses of Brachypodium distachyon to fluctuating nitrogen availability

The Nitrogen Use Efficiency (NUE) of grain cereals depends on nitrate (NO₃^-) 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 NO₃^- availability. As previously described in wheat and barley, we show that vegetative growth, shoot/root ratio, tiller formation, spike development, tissue NO₃^- and N contents, grain number per plant, grain yield and grain N content are sensitive to pre- and/or post-anthesis NO₃^- supply. We subsequently described constitutive and NO₃^--inducible components of both High and Low Affinity Transport Systems (HATS and LATS) for root NO₃^- 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 NO₃^- uptake and efficient constitutive HATS, further identify Brachypodium as a direct source of knowledge for crop improvement.