Post-translational regulation of cytosolic glutamine synthetase by reversible phosphorylation and 14-3-3 protein interaction

Plant J. 2000 Oct;24(2):171-81. doi: 10.1046/j.1365-313x.2000.00863.x.


Regulation of the cytosolic isozyme of glutamine synthetase (GS(1); EC was studied in leaves of Brassica napus L. Expression and immunodetection studies showed that GS(1) was the only active GS isozyme in senescing leaves. By use of [gamma-(32)P]ATP followed by immunodetection, it was shown that GS(1) is a phospho-protein. GS(1) is regulated post-translationally by reversible phosphorylation catalysed by protein kinases and microcystin-sensitive serine/threonine protein phosphatases. Dephosphorylated GS(1) is much more susceptible to degradation than the phosphorylated form. The phosphorylation status of GS(1) changes during light/dark transitions and depends in vitro on the ATP/AMP ratio. Phosphorylated GS(1) interacts with 14-3-3 proteins as verified by two different methods: a His-tag 14-3-3 protein column affinity method combined with immunodetection, and a far-Western method with overlay of 14-3-3-GFP. The degree of interaction with 14-3-3-proteins could be modified in vitro by decreasing or increasing the phosphorylation status of GS(1). Thus, the results demonstrate that 14-3-3 protein is an activator molecule of cytosolic GS and provide the first evidence of a protein involved in the activation of plant cytosolic GS. The role of post-translational regulation of cytosolic GS and interactions between phosphorylated cytosolic GS and 14-3-3 proteins in senescing leaves is discussed in relation to nitrogen remobilization.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • 14-3-3 Proteins
  • Biological Transport
  • Brassica / genetics*
  • Cytosol / enzymology*
  • Darkness
  • Gene Expression Regulation, Enzymologic
  • Glutamate-Ammonia Ligase / genetics*
  • Light
  • Models, Biological
  • Molecular Sequence Data
  • Nitrogen / metabolism
  • Phosphoproteins / metabolism
  • Phosphorylation
  • Plant Leaves / enzymology
  • Plant Proteins / metabolism
  • Protein Processing, Post-Translational*
  • Protein Subunits
  • Tyrosine 3-Monooxygenase / metabolism*


  • 14-3-3 Proteins
  • Phosphoproteins
  • Plant Proteins
  • Protein Subunits
  • Tyrosine 3-Monooxygenase
  • Glutamate-Ammonia Ligase
  • Nitrogen

Associated data

  • GENBANK/AF111812
  • GENBANK/X72751
  • GENBANK/X76736
  • GENBANK/X82997