Gene expression, cellular localisation and function of glutamine synthetase isozymes in wheat (Triticum aestivum L.).
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.
Bernard
Stéphanie M
SM
Plant Science Department, Centre for Crop Genetic Improvement, Rothamsted Research, Harpenden, Hertfordshire, UK.
Møller
Anders Laurell Blom
AL
Dionisio
Giuseppe
G
Kichey
Thomas
T
Jahn
Thomas P
TP
Dubois
Frederic
F
Baudo
Marcela
M
Lopes
Marta S
MS
Tercé-Laforgue
Thérèse
T
Foyer
Christine H
CH
Parry
Martin A J
MA
Forde
Brian G
BG
Araus
Jose Luis
JL
Hirel
Bertrand
B
Schjoerring
Jan K
JK
Habash
Dimah Z
DZ
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
D010940:Plant Proteins; D005974:Glutamate-Ammonia Ligase