title: Regulation of NH4+ transport by essential cross talk between AMT monomers through the carboxyl tails.
abstract: Ammonium transport across plant plasma membranes is facilitated by AMT/Rh-type ammonium transporters (AMTs), which also have homologs in most organisms. In the roots of the plant Arabidopsis (Arabidopsis thaliana), AMTs have been identified that function directly in the high-affinity NH4+ acquisition from soil. Here, we show that AtAMT1;2 has a distinct role, as it is located in the plasma membrane of the root endodermis. AtAMT1;2 functions as a comparatively low-affinity NH4+ transporter. Mutations at the highly conserved carboxyl terminus (C terminus) of AMTs, including one that mimics phosphorylation at a putative phosphorylation site, impair NH4+ transport activity. Coexpressing these mutants along with wild-type AtAMT1;2 substantially reduced the activity of the wild-type transporter. A molecular model of AtAMT1;2 provides a plausible explanation for the dominant inhibition, as the C terminus of one monomer directly contacts the neighboring subunit. It is suggested that part of the cytoplasmic C terminus of a single monomer can gate the AMT trimer. This regulatory mechanism for rapid and efficient inactivation of NH4+ transporters may apply to several AMT members to prevent excess influx of cytotoxic ammonium.
authors.affiliation: Zentrum für Molekularbiologie der Pflanzen, Pflanzenphysiologie, Universität Tübingen, D-72076 Tuebingen, Germany.
authors.forename: Benjamin
authors.initials: B
authors.lastname: Neuhäuser
authors.forename: Marek
authors.initials: M
authors.lastname: Dynowski
authors.forename: Maria
authors.initials: M
authors.lastname: Mayer
authors.forename: Uwe
authors.initials: U
authors.lastname: Ludewig
mesh_terms: D017360:Arabidopsis / Q000378:metabolism; D001692:Biological Transport; D027682:Cation Transport Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D008958:Models, Molecular; D009154:Mutation; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D018517:Plant Roots / Q000378:metabolism; D000644:Quaternary Ammonium Compounds / Q000378:metabolism*; D013696:Temperature
chemical_list: D027682:Cation Transport Proteins; D010940:Plant Proteins; D000644:Quaternary Ammonium Compounds; C088952:ammonium transporters, plant