A high-affinity ammonium transporter from the mycorrhizal ascomycete Tuber borchii

An ammonium transporter cDNA, named TbAMT1, was isolated from the ectomycorrhizal ascomycetous truffle Tuber borchii. The polypeptide encoded by TbAMT1 (52 kDa) functionally complements ammonium uptake-defective yeast mutants and shares sequence similarity with previously characterized ammonium tran...

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Bibliographic Details
Published in:Fungal genetics and biology 2002-06, Vol.36 (1), p.22-34
Main Authors: Montanini, Barbara, Moretto, Nadia, Soragni, Elisabetta, Percudani, Riccardo, Ottonello, Simone
Format: Article
Language:English
Subjects:
Amino Acid Sequence
Ammonium transporter
Ascomycota - genetics
Ascomycota - metabolism
Base Sequence
Carrier Proteins - genetics
Carrier Proteins - isolation & purification
Carrier Proteins - metabolism
Cation Transport Proteins
DNA, Complementary - genetics
DNA, Complementary - isolation & purification
DNA, Fungal - genetics
DNA, Fungal - isolation & purification
Fungal Proteins - genetics
Fungal Proteins - isolation & purification
Fungal Proteins - metabolism
Genes, Fungal
Genetic Complementation Test
Kinetics
Models, Molecular
Molecular Sequence Data
Mycorrhizal fungi
Nitrate
Nitrogen
Nutrient-regulated expression
Permease
Phylogeny
Plant Proteins
Protein Structure, Secondary
Quaternary Ammonium Compounds - metabolism
RNA, Fungal - genetics
RNA, Fungal - metabolism
RNA, Messenger - genetics
RNA, Messenger - metabolism
Truffles
Tuber borchii
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Summary:An ammonium transporter cDNA, named TbAMT1, was isolated from the ectomycorrhizal ascomycetous truffle Tuber borchii. The polypeptide encoded by TbAMT1 (52 kDa) functionally complements ammonium uptake-defective yeast mutants and shares sequence similarity with previously characterized ammonium transporters from Saccharomyces (Mep) and Arabidopsis (AtAMT1). Structural characteristics common to the Mep/Amt family and peculiar features of the Tuber transporter have been evidenced by a detailed topological model of the TbAMT1 protein, which predicts 11 transmembrane helices with an N terminus OUT/C terminus IN orientation. As revealed by uptake/competition experiments conducted in yeast, TbAMT1 is a high-affinity transporter with an apparent K m for ammonium of 2 μM . The TbAMT1 mRNA was very slowly, yet specifically upregulated in nitrogen-deprived T. borchii mycelia. Instead, a much faster return to basal expression levels was observed upon resupplementation of either ammonium or nitrate, which thus appear to be utilized as equally effective nitrogen sources by Tuber mycelia.
ISSN:1087-1845
1096-0937
DOI:10.1016/S1087-1845(02)00001-4