Abstract
We report the cloning and characterization of the first NH 4 + transporter gene ( GintAMT1) in an arbuscular mycorrhizal fungus. GintAMT1 encodes a polypeptide of 479 amino acids sharing high sequence similarity with previously characterized NH 4 + transporters from other fungi. Heterologous expression of GintAMT1 in the yeast triple mep mutant complemented the defect of this strain to grow in the presence of less than 1 mM NH 4 +. As revealed by [ 14C]methylammonium uptake experiments carried out in yeast, GintAMT1 encodes a high-affinity NH 4 + transporter. In mycelia developed in the presence of 0.9 mM NO 3 −, GintAMT1 transcription was increased after the addition of 30 μM NH 4 + but decreased after the addition of 3 mM NH 4 +. However, in mycelia grown in the presence of higher N concentrations, GintAMT1 transcripts decreased after the addition of NH 4 +, irrespective of the concentration used. These data suggest that GintAMT1 is involved in NH 4 + uptake by the extraradical mycelia from the surrounding media when it is present at micromolar concentrations.
Published Version
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