title: Characterization of three functional high-affinity ammonium transporters in Lotus japonicus with differential transcriptional regulation and spatial expression.
abstract: Ammonium is a primary source of nitrogen for plants. In legume plants ammonium can also be obtained by symbiotic nitrogen fixation, and NH(4)(+) is also a regulator of early and late symbiotic interaction steps. Ammonium transporters are likely to play important roles in the control of nodule formation as well as in nitrogen assimilation. Two new genes, LjAMT1;2 and LjAMT1;3, were cloned from Lotus japonicus. Both were able to complement the growth defect of a yeast (Saccharomyces cerevisiae) ammonium transport mutant. Measurement of [(14)C]methylammonium uptake rates and competition experiments revealed that each transporter had a high affinity for NH(4)(+). The K(i) for ammonium was 1.7, 3, and 15 microm for LjAMT1;1, 1;2, and 1;3, respectively. Real-time PCR revealed higher expression of LjAMT1;1, 1;2, and 1;3 genes in leaves than in roots and nodule, with expression levels decreasing in the order LjAMT1;1 > 1;2 > 1;3 except in flowers, in which LjAMT1;3 was expressed at higher level than in leaves, and LjAMT1;1 showed the lowest level of expression. Expression of LjAMT1;1 and 1;2 in roots was induced by nitrogen deprivation. Expression of LjAMT1;1 was repressed in leaves exposed to elevated CO(2) concentrations, which also suppress photorespiration. Tissue and cellular localization of LjAMT1 genes expression, using promoter-beta-glucuronidase and in situ RNA hybridization approaches, revealed distinct cellular spatial localization in different organs, including nodules, suggesting differential roles in the nitrogen metabolism of these organs.
authors.affiliation: Institute of Genetics and Biophysics, Via Marconi 12, 80125 Napoli, Italy.
authors.forename: Enrica
authors.initials: E
authors.lastname: D'Apuzzo
authors.forename: Alessandra
authors.initials: A
authors.lastname: Rogato
authors.forename: Ulrike
authors.initials: U
authors.lastname: Simon-Rosin
authors.forename: Hicham
authors.initials: H
authors.lastname: El Alaoui
authors.forename: Ani
authors.initials: A
authors.lastname: Barbulova
authors.forename: Marco
authors.initials: M
authors.lastname: Betti
authors.forename: Maria
authors.initials: M
authors.lastname: Dimou
authors.forename: Panagiotis
authors.initials: P
authors.lastname: Katinakis
authors.forename: Antonio
authors.initials: A
authors.lastname: Marquez
authors.forename: Anne-Marie
authors.initials: AM
authors.lastname: Marini
authors.forename: Michael K
authors.initials: MK
authors.lastname: Udvardi
authors.forename: Maurizio
authors.initials: M
authors.lastname: Chiurazzi
mesh_terms: D001483:Base Sequence; D002245:Carbon Dioxide / Q000494:pharmacology; D027682:Cation Transport Proteins / Q000235:genetics* / Q000378:metabolism; D018507:Gene Expression Regulation, Developmental / Q000187:drug effects; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D000070116:Lotus / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism; D008969:Molecular Sequence Data; D009154:Mutation; D009584:Nitrogen / Q000494:pharmacology; D010940:Plant Proteins / Q000235:genetics* / Q000378:metabolism; D000644:Quaternary Ammonium Compounds / Q000378:metabolism; D012689:Sequence Homology, Nucleic Acid; D015003:Yeasts / Q000235:genetics / Q000378:metabolism
chemical_list: D027682:Cation Transport Proteins; D010940:Plant Proteins; D000644:Quaternary Ammonium Compounds; C088952:ammonium transporters, plant; D002245:Carbon Dioxide; D009584:Nitrogen