Symbiotic nitrogen fixation does not require adenylylation of glutamine synthetase I in Rhizobium meliloti.
Symbiotic nitrogen fixation is accompanied by a shift of Rhizobium nitrogen metabolism from ammonium assimilation to ammonium export, which probably involves genetic or metabolic regulation of glutamine synthetase activity. In free-living Rhizobium meliloti glutamine synthetase I (GSI) is regulated post-translationally by reversible adenylylation in response to ammonium addition. Moreover, full expression of the GSI gene glnA requires the transcriptional activator, NtrC. A glnA1 mutant synthesizing a non-adenylylatable GSI produces normal nitrogen-fixing nodules on alfalfa: GSI adenylylation is dispensable for symbiotic nitrogen fixation. This is rationalized by the observation that less GS protein is present in R. meliloti bacteroids than in free-living bacterial cells.
Arcondéguy
T
T
Laboratoire de Bíologie Moléculaire des Relations Plantes-Microorganismes, UMR 215 INRAICNRS, Chemin de Borde Rouge, Castanet-Tolosan, France.
Huez
I
I
Fourment
J
J
Kahn
D
D
D000250:Adenosine Phosphosulfate / Q000378:metabolism; D005974:Glutamate-Ammonia Ligase / Q000235:genetics / Q000378:metabolism*; D007700:Kinetics; D008969:Molecular Sequence Data; D016296:Mutagenesis / Q000502:physiology; D009586:Nitrogen Fixation / Q000502:physiology*; D010641:Phenotype; D000644:Quaternary Ammonium Compounds / Q000378:metabolism; D016962:Sinorhizobium meliloti / Q000201:enzymology* / Q000235:genetics; D013559:Symbiosis
D000644:Quaternary Ammonium Compounds; D000250:Adenosine Phosphosulfate; C081173:glutamine synthetase I; D005974:Glutamate-Ammonia Ligase