Summary The NATURAL RESISTANCE‐ASSOCIATED MACROPHAGE PROTEIN 1 (NRAMP1) transporter guarantees plant survival of manganese (Mn) deficiency by mediating Mn entry into root cells. Unlike other high‐affinity metal transporters, NRAMP1 is only slightly regulated at the transcriptional level. We show here that adequate Mn content in tissues is safeguarded through a tight control of the quantity of NRAMP1 present at the surface of root cells. Depending on Mn availability, an NRAMP1‐GFP fusion protein cycles dynamically between the plasma membrane (PM) and endosomal compartments. This involves a clathrin‐mediated endocytosis pathway, as disrupting this pathway in auxilin‐overexpressor lines prevents NRAMP1 internalization. Mutation of the phosphorylated serine residues 20, 22 and 24 in the cytosol‐exposed N terminus of NRAMP1 alters its membrane distribution. Indeed, a phospho‐dead mutation stabilizes NRAMP1 at the PM, regardless of the Mn regime, and dramatically reduces plant tolerance to Mn toxicity. Conversely a phosphomimetic mutant is constitutively internalized into endosomes. Together, these data establish that phosphorylation of NRAMP1 is the trigger for its Mn‐induced endocytosis and represents the main level of regulation of this transporter. Furthermore, the extent of Mn toxicity observed when interrupting NRAMP1 membrane cycling undermines the dogma that Mn is only marginally toxic to plants.

Summary Manganese (Mn) is pivotal for plant growth and development but little is known about the processes that control its homeostasis in the cell. A spotlight on the pools of intracellular manganese and their cellular function has recently been gained through the characterization of new Mn transporters. In particular, transporters catalyzing the ins and outs of Mn at the various Golgi membranes have revealed the central role of the Golgi pool of Mn in the synthesis of the cell wall and as a reservoir for the numerous cellular Mn‐dependent pathways whose calibration relies on a set of Golgi‐resident transporters of the BICAT and NRAMP families.