title: The Kinase CIPK23 Inhibits Ammonium Transport inArabidopsis thaliana.
abstract: Ion transport in plants is not only strictly regulated on a transcriptional level, but it is also regulated posttranslationally. Enzyme modifications such as phosphorylation provide rapid regulation of many plant ion transporters and channels. Upon exposure to high ammonium concentrations in the rhizosphere, the high-affinity ammonium transporters (AMTs) inArabidopsis thalianaare efficiently inactivated by phosphorylation to avoid toxic accumulation of cytoplasmic ammonium. External ammonium stimulates the phosphorylation of a conserved threonine in the cytosolic AMT1 C terminus, which allosterically inactivates AMT1 trimers. Using a genetic screen, we found that CALCINEURIN B-LIKE INTERACTING PROTEIN KINASE23 (CIPK23), a kinase that also regulates the most abundant NO3-transporter, NPF6;3, and activates the K+channel AKT1, inhibits ammonium transport and modulates growth sensitivity to ammonium. Loss ofCIPK23increased root NH4+uptake after ammonium shock and conferred hypersensitivity to ammonium and to the transport analog methylammonium. CIPK23 interacts with AMT1;1 and AMT1;2 in yeast, oocytes, and in planta. Inactivation of AMT1;2 by direct interaction with CIPK23 requires kinase activity and the calcineurin B-like binding protein CBL1. Since K+, NO3-, and NH4+are major ions taken up by plants, CIPK23 appears to occupy a key position in controlling ion balance and ion homeostasis in the plant cell.
authors.affiliation: Institute of Crop Science, Nutritional Crop Physiology, University of Hohenheim, D-70593 Stuttgart, Germany.
authors.forename: Tatsiana
authors.initials: T
authors.lastname: Straub
authors.affiliation: Institute of Crop Science, Nutritional Crop Physiology, University of Hohenheim, D-70593 Stuttgart, Germany.
authors.forename: Uwe
authors.identifier: 0000-0001-5456-1055
authors.initials: U
authors.lastname: Ludewig
authors.affiliation: Institute of Crop Science, Nutritional Crop Physiology, University of Hohenheim, D-70593 Stuttgart, Germany benjamin.neuhaeuser@uni-hohenheim.de.
authors.forename: Benjamin
authors.identifier: 0000-0002-2391-0598
authors.initials: B
authors.lastname: Neuhäuser
mesh_terms: D064751:Ammonium Compounds / Q000378:metabolism*; D000818:Animals; D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D001692:Biological Transport; D027682:Cation Transport Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D018506:Gene Expression Regulation, Plant; D016254:Mutagenesis, Insertional; D009154:Mutation; D010641:Phenotype; D010766:Phosphorylation; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D014982:Xenopus laevis
chemical_list: D064751:Ammonium Compounds; D029681:Arabidopsis Proteins; D027682:Cation Transport Proteins; D010940:Plant Proteins; C088952:ammonium transporters, plant; C514581:CIPK23 protein, Arabidopsis; D017346:Protein Serine-Threonine Kinases