Two cytosolic glutamine synthetase isoforms of maize are specifically involved in the control of grain production.
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.
Martin
Antoine
A
Unité de Nutrition Azotée des Plantes UR511, Institut National de la Recherche Agronomique, F-78026 Versailles Cedex, France.
Lee
Judy
J
Kichey
Thomas
T
Gerentes
Denise
D
Zivy
Michel
M
Tatout
Christophe
C
Dubois
Frédéric
F
Balliau
Thierry
T
Valot
Benoît
B
Davanture
Marlène
M
Tercé-Laforgue
Thérèse
T
Quilleré
Isabelle
I
Coque
Marie
M
Gallais
André
A
Gonzalez-Moro
María-Begoña
MB
Bethencourt
Linda
L
Habash
Dimah Z
DZ
Lea
Peter J
PJ
Charcosset
Alain
A
Perez
Pascual
P
Murigneux
Alain
A
Sakakibara
Hitoshi
H
Edwards
Keith J
KJ
Hirel
Bertrand
B
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
D007527:Isoenzymes; D021122:Protein Subunits; D012333:RNA, Messenger; D005974:Glutamate-Ammonia Ligase