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Eukaryotic Cell, March 2006, p. 480-487, Vol. 5, No. 3
1535-9778/06/$08.00+0     doi:10.1128/EC.5.3.480-487.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

Role of a Mitogen-Activated Protein Kinase Cascade in Ion Flux-Mediated Turgor Regulation in Fungi

Roger R. Lew,1,{dagger}* Natalia N. Levina,1 Lana Shabala,2 Marinela I. Anderca,1 and Sergey N. Shabala2,{dagger}

Department of Biology, York University, Toronto, Ontario, Canada,1 School of Agricultural Science, University of Tasmania, Hobart, Australia2

Received 1 October 2005/ Accepted 20 December 2005

Fungi normally maintain a high internal hydrostatic pressure (turgor) of about 500 kPa. In response to hyperosmotic shock, there are immediate electrical changes: a transient depolarization (1 to 2 min) followed by a sustained hyperpolarization (5 to 10 min) prior to turgor recovery (10 to 60 min). Using ion-selective vibrating probes, we established that the transient depolarization is due to Ca2+ influx and the sustained hyperpolarization is due to H+ efflux by activation of the plasma membrane H+-ATPase. Protein synthesis is not required for H+-ATPase activation. Net K+ and Cl– uptake occurs at the same time as turgor recovery. The magnitude of the ion uptake is more than sufficient to account for the osmotic gradients required for turgor to return to its original level. Two osmotic mutants, os-1 and os-2, homologs of a two-component histidine kinase sensor and the yeast high osmotic glycerol mitogen-activated protein (MAP) kinase, respectively, have lower turgor than the wild type and do not exhibit the sustained hyperpolarization after hyperosmotic treatment. The os-1 mutant does not exhibit all of the wild-type turgor-adaptive ion fluxes (Cl– uptake increases, but net K+ flux barely changes and net H+ efflux declines) (os-2 was not examined). Both os mutants are able to regulate turgor but at a lower level than the wild type. Our results demonstrate that a MAP kinase cascade regulates ion transport, activation of the H+-ATPase, and net K+ and Cl– uptake during turgor regulation. Other pathways regulating turgor must also exist.

* Corresponding author. Mailing address: Department of Biology, York University, 4700 Keele Street, Toronto, Ontario M3J 1P3, Canada. Phone: (416) 736-5243. Fax: (416) 736-5698. E-mail: planters{at}yorku.ca.

{dagger} R.R.L. and S.N.S. contributed equally to the research through a collaborative Australian Research Council International Linkage grant.

Eukaryotic Cell, March 2006, p. 480-487, Vol. 5, No. 3
1535-9778/06/$08.00+0     doi:10.1128/EC.5.3.480-487.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Lew, R. R., Nasserifar, S. (2009). Transient responses during hyperosmotic shock in the filamentous fungus Neurospora crassa. Microbiology 155: 903-911 [Abstract] [Full Text]  
  • Lew, R. R., Abbas, Z., Anderca, M. I., Free, S. J. (2008). Phenotype of a Mechanosensitive Channel Mutant, mid-1, in a Filamentous Fungus, Neurospora crassa. Eukaryot Cell 7: 647-655 [Abstract] [Full Text]  
  • Lew, R. R. (2007). Ionic currents and ion fluxes in Neurospora crassa hyphae. J Exp Bot 0: erm204v1-erm204 [Abstract] [Full Text]  
  • Jones, C. A., Greer-Phillips, S. E., Borkovich, K. A. (2007). The Response Regulator RRG-1 Functions Upstream of a Mitogen-activated Protein Kinase Pathway Impacting Asexual Development, Female Fertility, Osmotic Stress, and Fungicide Resistance in Neurospora crassa. Mol. Biol. Cell 18: 2123-2136 [Abstract] [Full Text]  
  • Lew, R. R., Levina, N. N. (2007). Turgor regulation in the osmosensitive cut mutant of Neurospora crassa. Microbiology 153: 1530-1537 [Abstract] [Full Text]  


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