title: Cytosolic glutamine synthetase1;2 is responsible for the primary assimilation of ammonium in rice roots.
abstract: Among three genes for cytosolic glutamine synthetase (OsGS1;1, OsGS1;2 and OsGS1;3) in rice (Oryza sativa L.) plants, the OsGS1;2 gene is known to be mainly expressed in surface cells of roots, but its function was not clearly understood. We characterized knock-out mutants caused by the insertion of an endogenous retrotransposon Tos17 into exon 2 of OsGS1;2. Homozygously inserted mutants showed severe reduction in active tiller number and hence panicle number at harvest. Other yield components, such as spikelet number per panicle, 1,000-spikelet weight and proportion of well ripened grains, were nearly identical between the mutants and wild-type plants. When the contents of free amino acids in roots were compared between the mutants and the wild type, there were marked reductions in contents of glutamine, glutamate, asparagine and aspartate, but a remarkable increase in free ammonium ions in the mutants. Concentrations of amino acids and ammonium ions in xylem sap behaved in a similar fashion. Re-introduction of OsGS1;2 cDNA under the control of its own promoter into the knock-out mutants successfully restored yield components to wild-type levels as well as ammonium concentration in xylem sap. The results indicate that GS1;2 is important in the primary assimilation of ammonium ions taken up by rice roots, with GS1;1 in the roots unable to compensate for GS1;2 functions.
authors.affiliation: Graduate School of Agricultural Science, Tohoku University, 1-1 Tsutsumidori-Amamiyamachi, Aoba-ku, Sendai, 981-8555 Japan.
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Funayama
authors.forename: Soichi
authors.initials: S
authors.lastname: Kojima
authors.forename: Mayumi
authors.initials: M
authors.lastname: Tabuchi-Kobayashi
authors.forename: Yuki
authors.initials: Y
authors.lastname: Sawa
authors.forename: Yosuke
authors.initials: Y
authors.lastname: Nakayama
authors.forename: Toshihiko
authors.initials: T
authors.lastname: Hayakawa
authors.forename: Tomoyuki
authors.initials: T
authors.lastname: Yamaya
mesh_terms: D000596:Amino Acids / Q000378:metabolism; D064751:Ammonium Compounds / Q000378:metabolism*; D003600:Cytosol / Q000201:enzymology*; D018076:DNA, Complementary / Q000235:genetics; D015971:Gene Expression Regulation, Enzymologic; D018506:Gene Expression Regulation, Plant; D055786:Gene Knockout Techniques; D005816:Genetic Complementation Test; D005974:Glutamate-Ammonia Ligase / Q000235:genetics / Q000378:metabolism*; D009154:Mutation / Q000235:genetics; D012275:Oryza / Q000201:enzymology* / Q000235:genetics; D010641:Phenotype; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D018517:Plant Roots / Q000235:genetics / Q000378:metabolism*; D060888:Real-Time Polymerase Chain Reaction; D052584:Xylem / Q000378:metabolism
chemical_list: D000596:Amino Acids; D064751:Ammonium Compounds; D018076:DNA, Complementary; D010940:Plant Proteins; D005974:Glutamate-Ammonia Ligase
keywords: Ammonium assimilation; Cytosolic glutamine synthetas; Metabolism; Mutant; Rice; Yield