Metabolic profiling of maize mutants deficient for two glutamine synthetase isoenzymes using 1H-NMR-based metabolomics.
BACKGROUND
Maize mutants deficient for the expression of two genes encoding cytosolic glutamine synthetase (GS) isoenzymes GS1.3 and GS1.4 displayed reduced kernel number and kernel size, respectively, the effect of the mutation being cumulative in the double mutant. However, at maturity, shoot biomass production was not modified in all the mutants, indicating that the reaction catalysed by the enzyme is specifically involved in the control of grain yield.


OBJECTIVE
To examine the physiological impact of the GS mutations on the leaf metabolic profile during the kernel filling period, during which nitrogen is remobilized from the shoots to be further exported to the kernels.


METHODS
An (1)H-NMR spectroscopy metabolomic was applied to the investigation of metabolic change of the gln1.3, gln1.4 and gln1.3/1.4 double mutant.


RESULTS
In the three GS mutants, an increase in the amount of several N-containing metabolites such as asparagine, alanine, threonine and phophatidylcholine was observed whatever the level of nitrogen fertilisation. In addition, we found an accumulation of phenylalanine and tyrosine, two metabolites involved the primary steps of the phenylpropanoid pathway.


CONCLUSIONS
Changes in the metabolic profile of the GS mutants suggest that, when cytosolic GS activity is strongly reduced, either alternative metabolic pathways participate in the reassimilation of ammonium released during leaf protein remobilization or that premature leaf senescence is induced when kernel set and kernel filling are affected. The accumulation of phenylalanine and tyrosine in the mutant plants indicates that lignin biosynthesis is altered, thus possibly affecting ear development.
Broyart
Caroline
C
EA 3900-BioPI Biologie des Plantes et Contrôle des Insectes Ravageurs, Faculté de Pharmacie, 1, rue des Louvels et Faculté des Sciences, 33, rue Saint Leu, 80037 Amiens cedex 1, France.
Fontaine
Jean-Xavier
JX
Molinié
Roland
R
Cailleu
Dominique
D
Tercé-Laforgue
Thérèse
T
Dubois
Frédéric
F
Hirel
Bertrand
B
Mesnard
François
F
D005974:Glutamate-Ammonia Ligase / Q000235:genetics / Q000378:metabolism*; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism*; D055432:Metabolomics; D009154:Mutation; D019906:Nuclear Magnetic Resonance, Biomolecular / Q000379:methods*; D011522:Protons; D003313:Zea mays / Q000235:genetics / Q000378:metabolism*
D007527:Isoenzymes; D011522:Protons; D005974:Glutamate-Ammonia Ligase