title: Gene expression, cellular localisation and function of glutamine synthetase isozymes in wheat (Triticum aestivum L.).
abstract: We present the first cloning and study of glutamine synthetase (GS) genes in wheat (Triticum aestivum L.). Based on sequence analysis, phylogenetic studies and mapping data, ten GS sequences were classified into four sub-families: GS2 (a, b and c), GS1 (a, b and c), GSr (1 and 2) and GSe (1 and 2). Phylogenetic analysis showed that the wheat GS sub-families together with the GS genes from other monocotyledonous species form four distinct clades. Immunolocalisation studies in leaves, stems and rachis in plants at flowering showed GS protein to be present in parenchyma, phloem companion and perifascicular sheath cells. In situ localisation confirmed that GS1 transcripts were present in the perifascicular sheath cells whilst those for GSr were confined to the vascular cells. Studies of the expression and protein profiles showed that all GS sub-families were differentially expressed in the leaves, peduncle, glumes and roots. Expression of GS genes in leaves was developmentally regulated, with both GS2 and GS1 assimilating or recycling ammonia in leaves during the period of grain development and filling. During leaf senescence the cytosolic isozymes, GS1 and GSr, were the predominant forms, suggesting major roles in assimilating ammonia during the critical phases of remobilisation of nitrogen to the grain. A preliminary analysis of three different wheat genotypes showed that the ratio of leaf GS2 protein to GS1 protein was variable. Use of this genetic variation should inform future efforts to modulate this enzyme for pre-breeding efforts to improve nitrogen use in wheat.
authors.affiliation: Plant Science Department, Centre for Crop Genetic Improvement, Rothamsted Research, Harpenden, Hertfordshire, UK.
authors.forename: Stéphanie M
authors.initials: SM
authors.lastname: Bernard
authors.forename: Anders Laurell Blom
authors.initials: AL
authors.lastname: Møller
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Dionisio
authors.forename: Thomas
authors.initials: T
authors.lastname: Kichey
authors.forename: Thomas P
authors.initials: TP
authors.lastname: Jahn
authors.forename: Frederic
authors.initials: F
authors.lastname: Dubois
authors.forename: Marcela
authors.initials: M
authors.lastname: Baudo
authors.forename: Marta S
authors.initials: MS
authors.lastname: Lopes
authors.forename: Thérèse
authors.initials: T
authors.lastname: Tercé-Laforgue
authors.forename: Christine H
authors.initials: CH
authors.lastname: Foyer
authors.forename: Martin A J
authors.initials: MA
authors.lastname: Parry
authors.forename: Brian G
authors.initials: BG
authors.lastname: Forde
authors.forename: Jose Luis
authors.initials: JL
authors.lastname: Araus
authors.forename: Bertrand
authors.initials: B
authors.lastname: Hirel
authors.forename: Jan K
authors.initials: JK
authors.lastname: Schjoerring
authors.forename: Dimah Z
authors.initials: DZ
authors.lastname: Habash
mesh_terms: D000595:Amino Acid Sequence; D003001:Cloning, Molecular; D003600:Cytosol / Q000201:enzymology; D018507:Gene Expression Regulation, Developmental; D018506:Gene Expression Regulation, Plant; D005838:Genotype; D005974:Glutamate-Ammonia Ligase / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D008969:Molecular Sequence Data; D005810:Multigene Family; D052585:Phloem / Q000201:enzymology / Q000502:physiology / Q000648:ultrastructure; D010802:Phylogeny; D018515:Plant Leaves / Q000201:enzymology / Q000502:physiology / Q000648:ultrastructure; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D018547:Plant Stems / Q000201:enzymology / Q000502:physiology / Q000648:ultrastructure; D016415:Sequence Alignment; D014908:Triticum / Q000201:enzymology* / Q000502:physiology / Q000648:ultrastructure
chemical_list: D010940:Plant Proteins; D005974:Glutamate-Ammonia Ligase