Characterization of a NADH-dependent glutamate dehydrogenase mutant of Arabidopsis demonstrates the key role of this enzyme in root carbon and nitrogen metabolism.
The role of NADH-dependent glutamate dehydrogenase (GDH) was investigated by studying the physiological impact of a complete lack of enzyme activity in an Arabidopsis thaliana plant deficient in three genes encoding the enzyme. This study was conducted following the discovery that a third GDH gene is expressed in the mitochondria of the root companion cells, where all three active GDH enzyme proteins were shown to be present. A gdh1-2-3 triple mutant was constructed and exhibited major differences from the wild type in gene transcription and metabolite concentrations, and these differences appeared to originate in the roots. By placing the gdh triple mutant under continuous darkness for several days and comparing it to the wild type, the evidence strongly suggested that the main physiological function of NADH-GDH is to provide 2-oxoglutarate for the tricarboxylic acid cycle. The differences in key metabolites of the tricarboxylic acid cycle in the triple mutant versus the wild type indicated that, through metabolic processes operating mainly in roots, there was a strong impact on amino acid accumulation, in particular alanine, γ-aminobutyrate, and aspartate in both roots and leaves. These results are discussed in relation to the possible signaling and physiological functions of the enzyme at the interface of carbon and nitrogen metabolism.
Equipe d'Accueil 3900, Biologie des Plantes et Contrôle des Insectes Ravageurs, Faculté de Pharmacie, 80039 Amiens cedex 1, France.
Jean-Xavier
JX
Fontaine
Thérèse
T
Tercé-Laforgue
Patrick
P
Armengaud
Gilles
G
Clément
Jean-Pierre
JP
Renou
Sandra
S
Pelletier
Manuella
M
Catterou
Marianne
M
Azzopardi
Yves
Y
Gibon
Peter J
PJ
Lea
Bertrand
B
Hirel
Frédéric
F
Dubois
D000409:Alanine / Q000378:metabolism; D000429:Alcohol Oxidoreductases / Q000032:analysis / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics; D029681:Arabidopsis Proteins / Q000032:analysis / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D001224:Aspartic Acid / Q000378:metabolism; D002244:Carbon / Q000378:metabolism*; D002952:Citric Acid Cycle; D020869:Gene Expression Profiling; D007656:Ketoglutaric Acids / Q000378:metabolism; D008954:Models, Biological; D008969:Molecular Sequence Data; D009154:Mutation; D009584:Nitrogen / Q000378:metabolism*; D018515:Plant Leaves / Q000378:metabolism; D018517:Plant Roots / Q000378:metabolism*; D015398:Signal Transduction; D005680:gamma-Aminobutyric Acid / Q000378:metabolism
D029681:Arabidopsis Proteins; D007656:Ketoglutaric Acids; D001224:Aspartic Acid; D005680:gamma-Aminobutyric Acid; D002244:Carbon; D000429:Alcohol Oxidoreductases; C525353:GDH protein, Arabidopsis; D009584:Nitrogen; D000409:Alanine