Arabidopsis glt1-T mutant defines a role for NADH-GOGAT in the non-photorespiratory ammonium assimilatory pathway.
The physiological role of the NADH-dependent glutamine-2-oxoglutarate aminotransferase (NADH-GOGAT) enzyme was addressed in Arabidopsis using gene expression analysis and by the characterization of a knock-out T-DNA insertion mutant (glt1-T) in the single NADH-GOGAT GLT1 gene. The NADH-GOGAT GLT1 mRNA is expressed at higher levels in roots than in leaves. This expression pattern contrasts with GLU1, the major gene encoding Fd-GOGAT, which is most highly expressed in leaves and is involved in photorespiration. These distinct organ-specific expression patterns suggested a non-redundant physiological role for the NADH-GOGAT and Fd-GOGAT gene products. To test the in vivo function of NADH-GOGAT, we conducted molecular and physiological analysis of the glt1-T mutant, which is null for NADH-GOGAT, as judged by mRNA level and enzyme activity. Metabolic analysis showed that the glt1-T mutant has a specific defect in growth and glutamate biosynthesis when photorespiration was repressed by 1% CO2. Under these conditions, the glt1-T mutant displayed a 20% decrease in growth and a dramatic 70% reduction in glutamate levels. Herein, we discuss the significance of NADH-GOGAT in non-photorespiratory ammonium assimilation and in glutamate synthesis required for plant development.
Lancien
Muriel
M
Department of Biology, New York University, 100 Washington Square East, 1009 Main Building, New York, NY 10003, USA.
Martin
Melinda
M
Hsieh
Ming-Hsiun
MH
Leustek
Tom
T
Goodman
Howard
H
Coruzzi
Gloria M
GM
D000594:Amino Acid Oxidoreductases / Q000235:genetics / Q000502:physiology*; D000596:Amino Acids / Q000378:metabolism; D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics; D002245:Carbon Dioxide / Q000494:pharmacology; D002734:Chlorophyll / Q000378:metabolism; D004269:DNA, Bacterial / Q000235:genetics; D015971:Gene Expression Regulation, Enzymologic; D018506:Gene Expression Regulation, Plant; D050790:Glutamate Synthase (NADH); D018698:Glutamic Acid / Q000096:biosynthesis*; D005973:Glutamine / Q000096:biosynthesis; D008027:Light; D016254:Mutagenesis, Insertional; D009154:Mutation; D010101:Oxygen Consumption / Q000502:physiology; D010641:Phenotype; D018515:Plant Leaves / Q000187:drug effects / Q000378:metabolism / Q000528:radiation effects; D018517:Plant Roots / Q000187:drug effects / Q000378:metabolism / Q000528:radiation effects; D000644:Quaternary Ammonium Compounds / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism
D000596:Amino Acids; D004269:DNA, Bacterial; D000644:Quaternary Ammonium Compounds; D012333:RNA, Messenger; C036483:T-DNA; D005973:Glutamine; D002734:Chlorophyll; D002245:Carbon Dioxide; D018698:Glutamic Acid; D000594:Amino Acid Oxidoreductases; D050790:Glutamate Synthase (NADH); C042233:glutamate synthase (ferredoxin)