title: Additive contribution of AMT1;1 and AMT1;3 to high-affinity ammonium uptake across the plasma membrane of nitrogen-deficient Arabidopsis roots.
abstract: In Arabidopsis four root-expressed AMT genes encode functional ammonium transporters, which raises the question of their role in primary ammonium uptake. After pre-culturing under nitrogen-deficiency conditions, we quantified the influx of (15)N-labeled ammonium in T-DNA insertion lines and observed that the loss of either AMT1;1 or AMT1;3 led to a decrease in the high-affinity ammonium influx of approximately 30%. Under nitrogen-sufficient conditions the ammonium influx was lower in Columbia glabra compared with Wassilewskija (WS), and AMT1;1 did not contribute significantly to the ammonium influx in Col-gl. Ectopic expression of AMT1;3 under the control of a 35S promoter in either of the insertion lines amt1;3-1 or amt1;1-1 increased the ammonium influx above the level of their corresponding wild types. In transgenic lines carrying AMT-promoter-GFP constructs, the promoter activities of AMT1;1 and AMT1;3 were both upregulated under nitrogen-deficiency conditions and were localized to the rhizodermis, including root hairs. AMT gene-GFP fusions that were stably expressed under the control of their own promoters were localized to the plasma membrane. The double insertion line amt1;1-1amt1;3-1 showed a decreased sensitivity to the toxic ammonium analog methylammonium and a decrease in the ammonium influx of up to 70% relative to wild-type plants. These results suggest an additive contribution of AMT1;1 and AMT1;3 to the overall ammonium uptake capacity in Arabidopsis roots under nitrogen-deficiency conditions.
authors.affiliation: Molekulare Pflanzenernährung, Universität Hohenheim, D-70593 Stuttgart, Germany.
authors.forename: Dominique
authors.initials: D
authors.lastname: Loqué
authors.forename: Lixing
authors.initials: L
authors.lastname: Yuan
authors.forename: Soichi
authors.initials: S
authors.lastname: Kojima
authors.forename: Alain
authors.initials: A
authors.lastname: Gojon
authors.forename: Judith
authors.initials: J
authors.lastname: Wirth
authors.forename: Sonia
authors.initials: S
authors.lastname: Gazzarrini
authors.forename: Keiki
authors.initials: K
authors.lastname: Ishiyama
authors.forename: Hideki
authors.initials: H
authors.lastname: Takahashi
authors.forename: Nicolaus
authors.initials: N
authors.lastname: von Wirén
mesh_terms: D017360:Arabidopsis / Q000378:metabolism*; D001693:Biological Transport, Active; D027682:Cation Transport Proteins / Q000235:genetics / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant; D009584:Nitrogen / Q000378:metabolism*; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D018517:Plant Roots / Q000166:cytology* / Q000378:metabolism; D000644:Quaternary Ammonium Compounds / Q000378:metabolism*
chemical_list: D027682:Cation Transport Proteins; D010940:Plant Proteins; D000644:Quaternary Ammonium Compounds; C088952:ammonium transporters, plant; D009584:Nitrogen