title: Cytosolic Glutamine Synthetase Gln1;2 Is the Main Isozyme Contributing to GS1 Activity and Can Be Up-Regulated to Relieve Ammonium Toxicity.
abstract: Cytosolic GS1 (Gln synthetase) is central for ammonium assimilation in plants. High ammonium treatment enhanced the expression of the GS1 isogene Gln-1;2 encoding a low-affinity high-capacity GS1 protein in Arabidopsis (Arabidopsis thaliana) shoots. Under the same conditions, the expression of the high-affinity low-capacity isoform Gln-1;1 was reduced. The expression of Gln-1;3 did not respond to ammonium treatment while Gln-1;4 and Gln-1;5 isogenes in all cases were expressed at a very low level. Gln-2 was highly expressed in shoots but only at a very low level in roots. To investigate the specific functions of the two isogenes Gln-1;1 and Gln-1;2 in shoots for ammonium detoxification, single and double knock-out mutants were grown under standard N supply or with high ammonium provision. Phenotypes of the single mutant gln1;1 were similar to the wild type, while growth of the gln1;2 single mutant and the gln1;1:gln1;2 double mutant was significantly impaired irrespective of N regime. GS1 activity was significantly reduced in both gln1;2 and gln1;1:gln1;2 Along with this, the ammonium content increased while that of Gln decreased, showing that Gln-1;2 was essential for ammonium assimilation and amino acid synthesis. We conclude that Gln-1;2 is the main isozyme contributing to shoot GS1 activity in vegetative growth stages and can be up-regulated to relieve ammonium toxicity. This reveals, to our knowledge, a novel shoot function of Gln-1;2 in Arabidopsis shoots.
authors.affiliation: Department of Plant and Environmental Sciences and Copenhagen Plant Science Center, Faculty of Science, University of Copenhagen, DK-1871 Frederiksberg C, Denmark.
authors.forename: Miao
authors.identifier: 0000-0002-3927-6990
authors.initials: M
authors.lastname: Guan
authors.affiliation: Department of Plant and Environmental Sciences and Copenhagen Plant Science Center, Faculty of Science, University of Copenhagen, DK-1871 Frederiksberg C, Denmark.
authors.forename: Thomas C
authors.identifier: 0000-0002-5019-6422
authors.initials: TC
authors.lastname: de Bang
authors.affiliation: Department of Plant and Environmental Sciences and Copenhagen Plant Science Center, Faculty of Science, University of Copenhagen, DK-1871 Frederiksberg C, Denmark.
authors.forename: Carsten
authors.initials: C
authors.lastname: Pedersen
authors.affiliation: Department of Plant and Environmental Sciences and Copenhagen Plant Science Center, Faculty of Science, University of Copenhagen, DK-1871 Frederiksberg C, Denmark jks@plen.ku.dk.
authors.forename: Jan K
authors.identifier: 0000-0002-2852-3298
authors.initials: JK
authors.lastname: Schjoerring
mesh_terms: D000596:Amino Acids / Q000378:metabolism; D064751:Ammonium Compounds / Q000633:toxicity*; D017360:Arabidopsis / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D003600:Cytosol / Q000201:enzymology; D018506:Gene Expression Regulation, Plant; D005974:Glutamate-Ammonia Ligase / Q000235:genetics / Q000378:metabolism*; D008658:Inactivation, Metabolic; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism; D009154:Mutation; D009584:Nitrogen / Q000378:metabolism; D018520:Plant Shoots / Q000187:drug effects / Q000502:physiology; D030821:Plants, Genetically Modified; D015854:Up-Regulation / Q000187:drug effects
chemical_list: D000596:Amino Acids; D064751:Ammonium Compounds; D029681:Arabidopsis Proteins; D007527:Isoenzymes; C000616891:GLN1;2 protein, Arabidopsis; D005974:Glutamate-Ammonia Ligase; D009584:Nitrogen