Distinct osmo-sensing protein kinase pathways are involved in signalling moderate and severe hyper-osmotic stress

Teun Munnik, Wilco Ligterink, Irute Meskiene, Ornella Calderini, John Beyerly, Alan Musgrave, Heribert Hirt*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

148 Scopus citations


Plant growth is severely affected by hyper-osmotic salt conditions. Although a number of salt-induced genes have been isolated, the sensing and signal transduction of salt stress is little understood. We provide evidence that alfalfa cells have two osmo-sensing protein kinase pathways that are able to distinguish between moderate and extreme hyper-osmotic conditions. A 46 kDa protein kinase was found to be activated by elevated salt concentrations (above 125 mM NaCl). In contrast, at high salt concentrations (above 750 mM NaCl), a 38 kDa protein kinase, but not the 46 kDa kinase, became activated. By biochemical and immunological analysis, the 46 kDa kinase was identified as SIMK, a member of the family of MAPKs (mitogen-activated protein kinases). SIMK is not only activated by NaCl, but also by KCl and sorbitol, indicating that the SIMK pathway is involved in mediating general hyper-osmotic conditions. Salt stress induces rapid but transient activation of SIMK, showing maximal activity between 8 and 16 min before slow inactivation. When inactive, most mammalian and yeast MAPKs are cytoplasmic but undergo nuclear translocation upon activation. By contrast, SIMK was found to be a constitutively nuclear protein and the activity of the kinase was not correlated with changes in its intracellular compartmentation, suggesting an intra-nuclear mechanism for the regulation of SIMK activity.

Original languageEnglish (US)
Pages (from-to)381-388
Number of pages8
JournalPlant Journal
Issue number4
StatePublished - Nov 1999

ASJC Scopus subject areas

  • Genetics
  • Plant Science
  • Cell Biology

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