title: Nitrogen-dependent posttranscriptional regulation of the ammonium transporter AtAMT1;1.
abstract: Ammonium transporter (AMT) proteins of the AMT family mediate the transport of ammonium across plasma membranes. To investigate whether AMTs are regulated at the posttranscriptional level, a gene construct consisting of the cauliflower mosaic virus 35S promoter driving the Arabidopsis (Arabidopsis thaliana) AMT1;1 gene was introduced into tobacco (Nicotiana tabacum). Ectopic expression of AtAMT1;1 in transgenic tobacco lines led to high transcript levels and protein levels at the plasma membrane and translated into an approximately 30% increase in root uptake capacity for 15N-labeled ammonium in hydroponically grown transgenic plants. When ammonium was supplied as the major nitrogen (N) form but at limiting amounts to soil-grown plants, transgenic lines overexpressing AtAMT1;1 did not show enhanced growth or N acquisition relative to wild-type plants. Surprisingly, steady-state transcript levels of AtAMT1;1 accumulated to higher levels in N-deficient roots and shoots of transgenic tobacco plants in spite of expression being controlled by the constitutive 35S promoter. Moreover, steady-state transcript levels were decreased after addition of ammonium or nitrate in N-deficient roots, suggesting a role for N availability in regulating AtAMT1;1 transcript abundance. Nitrogen deficiency-dependent accumulation of AtAMT1;1 mRNA was also observed in 35S:AtAMT1;1-transformed Arabidopsis shoots but not in roots. Evidence for a regulatory role of the 3'-untranslated region of AtAMT1;1 alone in N-dependent transcript accumulation was not found. However, transcript levels of AtAMT1;3 did not accumulate in a N-dependent manner, even though the same T-DNA insertion line atamt1;1-1 was used for 35S:AtAMT1;3 expression. These results show that the accumulation of AtAMT1;1 transcripts is regulated in a N- and organ-dependent manner and suggest mRNA turnover as an additional mechanism for the regulation of AtAMT1;1 in response to the N nutritional status of plants.
authors.affiliation: Molecular Plant Nutrition, Institute of Plant Nutrition, University of Hohenheim, D-70593 Stuttgart, Germany.
authors.forename: Lixing
authors.initials: L
authors.lastname: Yuan
authors.forename: Dominique
authors.initials: D
authors.lastname: Loqué
authors.forename: Fanghua
authors.initials: F
authors.lastname: Ye
authors.forename: Wolf B
authors.initials: WB
authors.lastname: Frommer
authors.forename: Nicolaus
authors.initials: N
authors.lastname: von Wirén
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism*; D001693:Biological Transport, Active / Q000502:physiology; D027682:Cation Transport Proteins / Q000235:genetics / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D008744:Methylamines / Q000378:metabolism; D009584:Nitrogen / Q000378:metabolism* / Q000494:pharmacology; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D030821:Plants, Genetically Modified; D000644:Quaternary Ammonium Compounds / Q000378:metabolism; D012323:RNA Processing, Post-Transcriptional / Q000502:physiology*; D012333:RNA, Messenger / Q000378:metabolism; D014026:Nicotiana / Q000235:genetics / Q000378:metabolism
chemical_list: D027682:Cation Transport Proteins; D008744:Methylamines; D010940:Plant Proteins; D000644:Quaternary Ammonium Compounds; D012333:RNA, Messenger; C088952:ammonium transporters, plant; C027451:methylamine; D009584:Nitrogen