Journal Article

AtAMT1;4, a Pollen-Specific High-Affinity Ammonium Transporter of the Plasma Membrane in Arabidopsis

Lixing Yuan, Lucile Graff, Dominique Loqué, Soichi Kojima, Yumiko N. Tsuchiya, Hideki Takahashi and Nicolaus von Wirén

in Plant and Cell Physiology

Published on behalf of Japanese Society of Plant Physiologists

Volume 50, issue 1, pages 13-25
Published in print January 2009 | ISSN: 0032-0781
Published online December 2008 | e-ISSN: 1471-9053 | DOI: http://dx.doi.org/10.1093/pcp/pcn186
AtAMT1;4, a Pollen-Specific High-Affinity Ammonium Transporter of the Plasma Membrane in Arabidopsis

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  • Biochemistry
  • Molecular and Cell Biology
  • Plant Sciences and Forestry

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Pollen represents an important nitrogen sink in flowers to ensure pollen viability. Since pollen cells are symplasmically isolated during maturation and germination, membrane transporters are required for nitrogen import across the pollen plasma membrane. This study describes the characterization of the ammonium transporter AtAMT1;4, a so far uncharacterized member of the Arabidopsis AMT1 family, which is suggested to be involved in transporting ammonium into pollen. The AtAMT1;4 gene encodes a functional ammonium transporter when heterologously expressed in yeast or when overexpressed in Arabidopsis roots. Concentration-dependent analysis of 15N-labeled ammonium influx into roots of AtAMT1;4-transformed plants allowed characterization of AtAMT1;4 as a high-affinity transporter with a Km of 17 μM. RNA and protein gel blot analysis showed expression of AtAMT1;4 in flowers, and promoter–gene fusions to the green fluorescent protein (GFP) further defined its exclusive expression in pollen grains and pollen tubes. The AtAMT1;4 protein appeared to be localized to the plasma membrane as indicated by protein gel blot analysis of plasma membrane-enriched membrane fractions and by visualization of GFP-tagged AtAMT1;4 protein in pollen grains and pollen tubes. However, no phenotype related to pollen function could be observed in a transposon-tagged line, in which AtAMT1;4 expression is disrupted. These results suggest that AtAMT1;4 mediates ammonium uptake across the plasma membrane of pollen to contribute to nitrogen nutrition of pollen via ammonium uptake or retrieval.

Keywords: Ammonium uptake; AMTs; Germination; Nitrogen transport; Pollen; Pollen tube

Journal Article.  7273 words.  Illustrated.

Subjects: Biochemistry ; Molecular and Cell Biology ; Plant Sciences and Forestry

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