title: Contributions of two cytosolic glutamine synthetase isozymes to ammonium assimilation in Arabidopsis roots.
abstract: Glutamine synthetase (GS) catalyzes a reaction that incorporates ammonium into glutamate and yields glutamine in the cytosol and chloroplasts. Although the enzymatic characteristics of the GS1 isozymes are well known, their physiological functions in ammonium assimilation and regulation in roots remain unclear. In this study we show evidence that two cytosolic GS1 isozymes (GLN1;2 and GLN1;3) contribute to ammonium assimilation in Arabidopsis roots. Arabidopsis T-DNA insertion lines for GLN1;2 and GLN1;3 (i.e. gln1;2 and gln1;3 single-mutants), the gln1;2:gln1;3 double-mutant, and the wild-type accession (Col-0) were grown in hydroponic culture with variable concentrations of ammonium to compare their growth, and their content of nitrogen, carbon, ammonium, and amino acids. GLN1;2 and GLN1;3 promoter-dependent green fluorescent protein was observed under conditions with or without ammonium supply. Loss of GLN1;2 caused significant suppression of plant growth and glutamine biosynthesis under ammonium-replete conditions. In contrast, loss of GLN1;3 caused slight defects in growth and Gln biosynthesis that were only visible based on a comparison of the gln1;2 single- and gln1;2:gln1;3 double-mutants. GLN1;2, being the most abundantly expressed GS1 isozyme, markedly increased following ammonium supply and its promoter activity was localized at the cortex and epidermis, while GLN1;3 showed only low expression at the pericycle, suggesting their different physiological contributions to ammonium assimilation in roots. The GLN1;2 promoter-deletion analysis identified regulatory sequences required for controlling ammonium-responsive gene expression of GLN1;2 in Arabidopsis roots. These results shed light on GLN1 isozyme-specific regulatory mechanisms in Arabidopsis that allow adaptation to an ammonium-replete environment.
authors.affiliation: Graduate School of Agricultural Science, Tohoku University, 1-1 Tsutsumidori-Amamiyamachi, Sendai, Japan.
authors.forename: Noriyuki
authors.initials: N
authors.lastname: Konishi
authors.affiliation: Graduate School of Agricultural Science, Tohoku University, 1-1 Tsutsumidori-Amamiyamachi, Sendai, Japan.|RIKEN Plant Science Center, Yokohama, Japan.
authors.forename: Keiki
authors.initials: K
authors.lastname: Ishiyama
authors.affiliation: Graduate School of Agricultural Science, Tohoku University, 1-1 Tsutsumidori-Amamiyamachi, Sendai, Japan.
authors.forename: Marcel Pascal
authors.initials: MP
authors.lastname: Beier
authors.affiliation: RIKEN Plant Science Center, Yokohama, Japan.
authors.forename: Eri
authors.initials: E
authors.lastname: Inoue
authors.affiliation: Graduate School of Agricultural Science, Tohoku University, 1-1 Tsutsumidori-Amamiyamachi, Sendai, Japan.
authors.forename: Keiichi
authors.initials: K
authors.lastname: Kanno
authors.affiliation: Graduate School of Agricultural Science, Tohoku University, 1-1 Tsutsumidori-Amamiyamachi, Sendai, Japan.|RIKEN Plant Science Center, Yokohama, Japan.
authors.forename: Tomoyuki
authors.initials: T
authors.lastname: Yamaya
authors.affiliation: RIKEN Plant Science Center, Yokohama, Japan.|Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, MI, USA.
authors.forename: Hideki
authors.initials: H
authors.lastname: Takahashi
authors.affiliation: Graduate School of Agricultural Science, Tohoku University, 1-1 Tsutsumidori-Amamiyamachi, Sendai, Japan.|RIKEN Plant Science Center, Yokohama, Japan.
authors.forename: Soichi
authors.initials: S
authors.lastname: Kojima
mesh_terms: D064751:Ammonium Compounds / Q000378:metabolism*; D017360:Arabidopsis / Q000235:genetics* / Q000378:metabolism; D003600:Cytosol; D005974:Glutamate-Ammonia Ligase / Q000235:genetics* / Q000378:metabolism; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism; D010940:Plant Proteins / Q000235:genetics* / Q000378:metabolism; D018517:Plant Roots / Q000378:metabolism
chemical_list: D064751:Ammonium Compounds; D007527:Isoenzymes; D010940:Plant Proteins; D005974:Glutamate-Ammonia Ligase
keywords: Ammonium; Arabidopsis; GS1; glutamine; nitrogen; root