The Rhizobium GstI protein reduces the NH4+ assimilation capacity of Rhizobium leguminosarum.
We show that the protein encoded by the glutamine synthetase translational inhibitor (gstI) gene reduces the NH4+ assimilation capacity of Rhizobium leguminosarum. In this organism, gstI expression is regulated by the ntr system, including the PII protein, as a function of the nitrogen (N) status of the cells. The GstI protein, when expressed from an inducible promoter, inhibits glutamine synthetase II (glnII) expression under all N conditions tested. The induction of gstI affects the growth of a glutamine synthetase I (glnA-) strain and a single amino acid substitution (W48D) results in the complete loss of GstI function. During symbiosis, gstI is expressed in young differentiating symbiosomes (SBs) but not in differentiated N2-fixing SBs. In young SBs, the PII protein modulates the transcription of NtrC-regulated genes such as gstI and glnII. The evidence presented herein strengthens the idea that the endocytosis of bacteria inside the cytoplasm of the host cells is a key step in the regulation of NH4+ metabolism.
Tatè
R
R
International Institute of Genetics and Biophysics, CNR, Naples, Italy.
Mandrich
L
L
Spinosa
M R
MR
Riccio
A
A
Lamberti
A
A
Iaccarino
M
M
Patriarca
E J
EJ
D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D001483:Base Sequence; D004269:DNA, Bacterial / Q000235:genetics; D007887:Fabaceae / Q000382:microbiology; D005798:Genes, Bacterial; D005974:Glutamate-Ammonia Ligase / Q000378:metabolism; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D009584:Nitrogen / Q000378:metabolism; D009586:Nitrogen Fixation / Q000235:genetics; D011401:Promoter Regions, Genetic; D000644:Quaternary Ammonium Compounds / Q000378:metabolism*; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*; D016961:Rhizobium leguminosarum / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D013559:Symbiosis
D001426:Bacterial Proteins; D004269:DNA, Bacterial; C414318:GstI protein, Rhizobium leguminosarum; D000644:Quaternary Ammonium Compounds; D012097:Repressor Proteins; C083818:glutamine synthetase 2; D005974:Glutamate-Ammonia Ligase; D009584:Nitrogen