"Sustainable agriculture means to maintain equilibrium between obtaining a product at the best possible yield and with the best possible quality at the same time that the minimum environmental impact is provoked. Among the major challenges that the European Commission Horizon 2020 describes to be faced by researchers in the near future for building a better society, resources efficiency and sustainable agriculture are two of them.Nitrate (NO3−) and ammonium (NH4+) are the main forms of nitrogen (N) available for plants. There is serious concern regarding NO3− loss in the field, giving rise to soil and water pollution and to global warming through emissions of nitrous oxide. In this framework, the use of ammonium-based fertilizers is a great opportunity to reduce environmental pollution effects of nitrate-based manures. The potential of NH4+ as N source for agriculture has been reconsidered alongside the search to improve N use efficiency by the Intergovernmental Panel on Climate Change (IPCC). However, plants have traditionally been bred under nitric or combined nitrogen nutrition provoking a negative selection pressure towards NH4+ assimilation. Indeed, NH4+ is toxic to animals, plants, and fungi when present in excess amounts.In this project, a multidisciplinary approach will be engaged to identify new molecular and genetic basis of ammonium use efficiency in plants. With this aim, 384 natural accessions of Arabidopsis will be phenotyped and a Genome Wide Association analysis will be launched to identify genetic determinants of ammonium use efficiency in Arabidopsis. In parallel, Arabidopsis genetic reprogramming during ammonium nutrition will be assayed by RNAseq. The more interesting candidate genes will be functionally validated. Importantly, the knowledge and results generated with Arabidopsis as model plant will be transferred to economically important crops (wheat and tomato)."