1 SCIENTIFIC REPORTS | (2019) 9:3824 | https://doi.org/10.1038/s41598-019-40569-8 www.nature.com/scientificreports Developmental and physiological responses of Brachypodium distachyon to fuctuating nitrogen availability L. C. David, T. Girin , E. Fleurisson, E. Phommabouth, A. Mahfoudhi, S. Citerne, P. Berquin, F. Daniel-Vedele, A. Krapp & S. Ferrario-Méry The Nitrogen Use Efciency (NUE) of grain cereals depends on nitrate (NO 3 - ) 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 afects 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 3 - availability. As previously described in wheat and barley, we show that vegetative growth, shoot/root ratio, tiller formation, spike development, tissue NO 3 - and N contents, grain number per plant, grain yield and grain N content are sensitive to pre- and/or post- anthesis NO 3 - supply. We subsequently described constitutive and NO 3 - -inducible components of both High and Low Afnity Transport Systems (HATS and LATS) for root NO 3 - 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 specifcities such as high grain N content, strong post-anthesis NO 3 - uptake and efcient constitutive HATS, further identify Brachypodium as a direct source of knowledge for crop improvement. Te Poaceae family includes cereal crops such as wheat, rice, maize and barley, which provides a major source of food for humans and cattle. It is predicted that by 2050, the human population will increase by 20–50% in parallel to an increase of the living standard and thus, a doubling of grain demand is expected 1–3 . As arable land becomes limited, crop grain yields need to be improved. Nitrogen (N) is a major limiting macronutrient in the felds for crop production and as a consequence, N fertilizers are largely applied in modern agriculture to enhance plant vegetative growth and grain production. From an ecological point of view, the use of large amounts of N ferti- lizer on felds results in nitrate (NO 3 - ) leaching, which causes eutrophication and biodiversity depletion. Tus, increasing crop yields while diminishing environmental impacts of agriculture is a major goal of today’s agricul- ture. However, high-yielding modern cultivars are not suitable, as they have high nutrient requirements, due to their breeding under high nutrient availability 4,5 . Fundamental knowledge on molecular mechanisms of plant nutrition must be increased to engineer new cultivars giving high yields under low nutrient availability. Mechanisms directly afecting the plant Nitrogen Use Efciency (NUE) have been largely described at the physiological level in crop species (including wheat, barley, rice and corn) and in the model species, Arabidopsis thaliana (Arabidopsis) 6–9 . Most characterizations at the molecular level have however been restricted to the dicot Arabidopsis 10–12 . Brachypodium distachyon (Brachypodium) has been proposed as a good model to enhance this knowledge in C3 temperate cereals 13 . Tis non-domesticated monocot species ofers convenient characteristics for academic research (simple diploid sequenced genome, short life cycle, simple growth requirement, large mutant collections, efcient genetic transformation), and is phylogenetically closely related to wheat and barley, enabling an efcient translational approach. For grain crops, NUE is defned as the ratio between grain yield and available N in the soil per unit of feld surface, and is ofen approximated as the ratio between yield and added N 14 . It is dependent on processes such as Institut Jean-Pierre Bourgin, INRA, AgroParisTech, CNRS, Université Paris-Saclay, 78000, Versailles, France. L. C. David and T. Girin contributed equally. Correspondence and requests for materials should be addressed to T.G. (email: thomas.girin@inra.fr) Received: 8 May 2018 Accepted: 12 February 2019 Published: xx xx xxxx OPEN