Glutamine and alpha-ketoglutarate are metabolite signals involved in nitrate reductase gene transcription in untransformed and transformed tobacco plants deficient in ferredoxin-glutamine-alpha-ketoglutarate aminotransferase.
Transformed tobacco (Nicotiana tabacum L.) plants with varying activities of the key enzyme of ammonia assimilation, ferredoxin-glutamine-alpha-ketoglutarate aminotransferase (Fd-GOGAT; EC 1.4.7.1), were used to examine the roles of ammonium, glutamine (Gln) and alpha-ketoglutarate (alpha-KG) in the regulation of nitrate reductase (NR; EC 1.6.6.1) transcript abundance. In wild-type leaf discs, NR mRNA abundance was increased following feeding with NO3-, sucrose and alpha-KG and decreased by feeding Gln. In air, leaves with decreased GOGAT accumulated Gln and alpha-KG simultaneously; this was accompanied by increased NR transcripts. The inhibition of NR transcription by Gln observed in leaf-disc experiments was therefore not observed in the low-Fd-GOGAT plants that accumulate Gln in vivo. The results suggest that the negative effect of Gln on NR transcript abundance was offset by high alpha-KG and that the relative amounts of alpha-KG and Gln are more important in controlling NR gene transcription than the concentration of either metabolite alone.
Ferrario-Méry
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S
Unité de Nutrition Azotée des Plantes, INRA de Versailles, France. ferrario@versailles.inra.fr
Masclaux
C
C
Suzuki
A
A
Valadier
M H
MH
Hirel
B
B
Foyer
C H
CH
D000594:Amino Acid Oxidoreductases / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant; D005973:Glutamine / Q000378:metabolism*; D066298:In Vitro Techniques; D007656:Ketoglutaric Acids / Q000378:metabolism*; D050901:Nitrate Reductase; D009565:Nitrate Reductases / Q000235:genetics* / Q000378:metabolism; D009566:Nitrates / Q000494:pharmacology; D010101:Oxygen Consumption; D018515:Plant Leaves / Q000235:genetics / Q000378:metabolism; D030821:Plants, Genetically Modified; D000644:Quaternary Ammonium Compounds / Q000378:metabolism; D012333:RNA, Messenger; D018749:RNA, Plant; D015398:Signal Transduction; D013395:Sucrose / Q000494:pharmacology; D014026:Nicotiana / Q000235:genetics* / Q000378:metabolism; D014158:Transcription, Genetic
D007656:Ketoglutaric Acids; D009566:Nitrates; D000644:Quaternary Ammonium Compounds; D012333:RNA, Messenger; D018749:RNA, Plant; D005973:Glutamine; D013395:Sucrose; D000594:Amino Acid Oxidoreductases; C042233:glutamate synthase (ferredoxin); D009565:Nitrate Reductases; D050901:Nitrate Reductase