title: Characterization of AMT-mediated high-affinity ammonium uptake in roots of maize (Zea mays L.).
abstract: High-affinity ammonium uptake in plant roots is mainly mediated by AMT1-type ammonium transporters, and their regulation varies depending on the plant species. In this study we aimed at characterizing AMT-mediated ammonium transport in maize, for which ammonium-based fertilizer is an important nitrogen (N) source. Two ammonium transporter genes, ZmAMT1;1a and ZmAMT1;3, were isolated from a maize root-specific cDNA library by functional complementation of an ammonium uptake-defective yeast mutant. Ectopic expression of both genes in an ammonium uptake-defective Arabidopsis mutant conferred high-affinity ammonium uptake capacities in roots with substrate affinities of 48 and 33 μM for ZmAMT1;1a and ZmAMT1;3, respectively. In situ hybridization revealed co-localization of both ZmAMT genes on the rhizodermis, suggesting an involvement in capturing ammonium from the rhizosphere. In N-deficient maize roots, influx increased significantly while ZmAMT expression did not. Ammonium resupply to N-deficient or nitrate-pre-cultured roots, however, rapidly enhanced both influx and ZmAMT transcript levels, revealing a substrate-inducible regulation of ammonium uptake. In conclusion, the two rhizodermis-localized transporters ZmAMT1;1a and ZmAMT1;3 are most probably the major components in the high-affinity transport system in maize roots. A particular regulatory feature is their persistent induction by ammonium rather than an up-regulation under N deficiency.
authors.affiliation: Department of Plant Nutrition, Key Laboratory of Plant-Soil Interactions, MOE, Center for Resources, Environment and Food Security, China Agricultural University, Beijing 100193, China.
authors.forename: Riliang
authors.initials: R
authors.lastname: Gu
authors.forename: Fengying
authors.initials: F
authors.lastname: Duan
authors.forename: Xia
authors.initials: X
authors.lastname: An
authors.forename: Fusuo
authors.initials: F
authors.lastname: Zhang
authors.forename: Nicolaus
authors.initials: N
authors.lastname: von Wirén
authors.forename: Lixing
authors.initials: L
authors.lastname: Yuan
mesh_terms: D064751:Ammonium Compounds / Q000378:metabolism*; D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism; D001692:Biological Transport; D015153:Blotting, Western; D027682:Cation Transport Proteins / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant; D005816:Genetic Complementation Test; D017403:In Situ Hybridization; D009154:Mutation; D010802:Phylogeny; D019441:Plant Epidermis / Q000235:genetics / Q000378:metabolism; D010940:Plant Proteins / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D018517:Plant Roots / Q000235:genetics / Q000378:metabolism*; D030821:Plants, Genetically Modified / Q000235:genetics / Q000378:metabolism; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D058441:Rhizosphere; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D003313:Zea mays / Q000235:genetics / Q000378:metabolism*
chemical_list: D064751:Ammonium Compounds; D027682:Cation Transport Proteins; D010940:Plant Proteins; D020033:Protein Isoforms; C088952:ammonium transporters, plant
keywords: AMT; High-affinity ammonium uptake; Maize roots; Membrane transport; Nitrogen nutrition; Transcriptional regulation