Ammonium nutrition interacts with iron homeostasis in Brachypodium distachyon.

Most plants species develop stress symptoms when exposed to high ammonium (NH4 +) concentrations. Root is the first organ in contact with high NH4 + and therefore the first barrier to cope with ammonium stress. In this work, we focused on root adaptation to ammonium nutrition in the model plant Brachypodium distachyon. Proteome analysis evidenced changes associated to primary metabolism, cell wall remodelling and redox homeostasis. In addition, it revealed a strong induction of proteins related to methionine (Met) metabolism and phytosiderophore (PS) synthesis in ammonium-fed plants. In agreement, we show how the nitrogen source impacts Met/S-adenosyl-Met and PS metabolic pathways together with increasing root iron (Fe) content. Nevertheless, ammonium-fed plants displayed higher sensitivity to Fe deficiency, suggesting ammonium nutrition triggers impaired Fe utilization and root-to-shoot transport, which entailed an induction in Fe-related responses. Overall, this work evidences the importance of Fe homeostasis during ammonium nutrition and paves a new route to better understand and improve plants ammonium use efficiency and tolerance.