First published online March 2, 2007; 10.1104/pp.106.094243
Plant Physiology 143:1651-1659 (2007)
© 2007 American Society of Plant Biologists
OPEN ACCESS ARTICLE
CELL BIOLOGY AND SIGNAL TRANSDUCTION
Regulation of NH4+ Transport by Essential Cross Talk between AMT Monomers through the Carboxyl Tails1,[C],[W],[OA]
Benjamin Neuhäuser,
Marek Dynowski,
Maria Mayer and
Uwe Ludewig*
Zentrum für Molekularbiologie der Pflanzen, Pflanzenphysiologie, Universität Tübingen, D–72076 Tuebingen, Germany
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.
1 This work was supported by the Deutsche Forschungsgemeinschaft (grant no. Lu673/7–1).
The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Uwe Ludewig (uwe.ludewig{at}zmbp.uni-tuebingen.de).
[C] Some figures in this article are displayed in color online but in black and white in the print edition.
[W] The online version of this article contains Web-only data.
[OA] Open Access articles can be viewed online without a subscription.
www.plantphysiol.org/cgi/doi/10.1104/pp.106.094243
* Corresponding author; e-mail uwe.ludewig{at}zmbp.uni-tuebingen.de; fax 49–7071–29–3287.
Received December 5, 2006;
accepted February 22, 2007;
published March 2, 2007.
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