Additive contribution of AMT1;1 and AMT1;3 to high-affinity ammonium uptake across the plasma membrane of nitrogen-deficient Arabidopsis roots.
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.
Loqué
Dominique
D
Molekulare Pflanzenernährung, Universität Hohenheim, D-70593 Stuttgart, Germany.
Yuan
Lixing
L
Kojima
Soichi
S
Gojon
Alain
A
Wirth
Judith
J
Gazzarrini
Sonia
S
Ishiyama
Keiki
K
Takahashi
Hideki
H
von Wirén
Nicolaus
N
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*
D027682:Cation Transport Proteins; D010940:Plant Proteins; D000644:Quaternary Ammonium Compounds; C088952:ammonium transporters, plant; D009584:Nitrogen