title: Two cytosolic glutamine synthetase isoforms of maize are specifically involved in the control of grain production.
abstract: The roles of two cytosolic maize glutamine synthetase isoenzymes (GS1), products of the Gln1-3 and Gln1-4 genes, were investigated by examining the impact of knockout mutations on kernel yield. In the gln1-3 and gln1-4 single mutants and the gln1-3 gln1-4 double mutant, GS mRNA expression was impaired, resulting in reduced GS1 protein and activity. The gln1-4 phenotype displayed reduced kernel size and gln1-3 reduced kernel number, with both phenotypes displayed in gln1-3 gln1-4. However, at maturity, shoot biomass production was not modified in either the single mutants or double mutants, suggesting a specific impact on grain production in both mutants. Asn increased in the leaves of the mutants during grain filling, indicating that it probably accumulates to circumvent ammonium buildup resulting from lower GS1 activity. Phloem sap analysis revealed that unlike Gln, Asn is not efficiently transported to developing kernels, apparently causing reduced kernel production. When Gln1-3 was overexpressed constitutively in leaves, kernel number increased by 30%, providing further evidence that GS1-3 plays a major role in kernel yield. Cytoimmunochemistry and in situ hybridization revealed that GS1-3 is present in mesophyll cells, whereas GS1-4 is specifically localized in the bundle sheath cells. The two GS1 isoenzymes play nonredundant roles with respect to their tissue-specific localization.
authors.affiliation: Unité de Nutrition Azotée des Plantes UR511, Institut National de la Recherche Agronomique, F-78026 Versailles Cedex, France.
authors.forename: Antoine
authors.initials: A
authors.lastname: Martin
authors.forename: Judy
authors.initials: J
authors.lastname: Lee
authors.forename: Thomas
authors.initials: T
authors.lastname: Kichey
authors.forename: Denise
authors.initials: D
authors.lastname: Gerentes
authors.forename: Michel
authors.initials: M
authors.lastname: Zivy
authors.forename: Christophe
authors.initials: C
authors.lastname: Tatout
authors.forename: Frédéric
authors.initials: F
authors.lastname: Dubois
authors.forename: Thierry
authors.initials: T
authors.lastname: Balliau
authors.forename: Benoît
authors.initials: B
authors.lastname: Valot
authors.forename: Marlène
authors.initials: M
authors.lastname: Davanture
authors.forename: Thérèse
authors.initials: T
authors.lastname: Tercé-Laforgue
authors.forename: Isabelle
authors.initials: I
authors.lastname: Quilleré
authors.forename: Marie
authors.initials: M
authors.lastname: Coque
authors.forename: André
authors.initials: A
authors.lastname: Gallais
authors.forename: María-Begoña
authors.initials: MB
authors.lastname: Gonzalez-Moro
authors.forename: Linda
authors.initials: L
authors.lastname: Bethencourt
authors.forename: Dimah Z
authors.initials: DZ
authors.lastname: Habash
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Lea
authors.forename: Alain
authors.initials: A
authors.lastname: Charcosset
authors.forename: Pascual
authors.initials: P
authors.lastname: Perez
authors.forename: Alain
authors.initials: A
authors.lastname: Murigneux
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Sakakibara
authors.forename: Keith J
authors.initials: KJ
authors.lastname: Edwards
authors.forename: Bertrand
authors.initials: B
authors.lastname: Hirel
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D003600:Cytosol / Q000201:enzymology*; D002523:Edible Grain / Q000191:economics* / Q000201:enzymology*; D015971:Gene Expression Regulation, Enzymologic; D018506:Gene Expression Regulation, Plant; D018745:Genome, Plant / Q000235:genetics; D005974:Glutamate-Ammonia Ligase / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D007527:Isoenzymes / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D008969:Molecular Sequence Data; D016254:Mutagenesis, Insertional; D009154:Mutation / Q000235:genetics; D010641:Phenotype; D052585:Phloem / Q000201:enzymology; D018515:Plant Leaves / Q000166:cytology / Q000201:enzymology / Q000648:ultrastructure; D018517:Plant Roots / Q000166:cytology / Q000201:enzymology; D018520:Plant Shoots / Q000201:enzymology; D021122:Protein Subunits / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D021381:Protein Transport; D040901:Proteomics; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D014158:Transcription, Genetic; D052584:Xylem / Q000201:enzymology; D003313:Zea mays / Q000166:cytology / Q000201:enzymology* / Q000648:ultrastructure
chemical_list: D007527:Isoenzymes; D021122:Protein Subunits; D012333:RNA, Messenger; D005974:Glutamate-Ammonia Ligase