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Eukaryotic Cell, August 2003, p. 699-707, Vol. 2, No. 4
1535-9778/03/$08.00+0     DOI: 10.1128/EC.2.4.699-707.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.

Environmental Suppression of Neurospora crassa cot-1 Hyperbranching: a Link between COT1 Kinase and Stress Sensing

Rena Gorovits and Oded Yarden*

Department of Plant Pathology and Microbiology, The Otto Warburg Center for Agricultural Biotechnology, Faculty of Agricultural, Food and Environmental Quality Sciences, The Hebrew University of Jerusalem, Rehovot 76100, Israel,

Received 3 February 2003/ Accepted 7 May 2003

cot-1 mutants belong to a class of Neurospora crassa colonial temperature-sensitive (cot) mutants that exhibit abnormal polar extension and branching patterns when grown at restrictive temperatures. cot-1 encodes a Ser/Thr protein kinase that is structurally related to the human myotonic dystrophy kinase which, when impaired, confers a disease that involves changes in cytoarchitecture and ion homeostasis. When grown under restrictive conditions, cot-1 cultures exhibited enhanced medium acidification rates, increased relative abundance of sodium, and increased intracellular glycerol content, indicating an ion homeostasis defect in a hyperbranching mutant. The application of ion transport blockers led to only mild suppression of the cot-1 phenotype. The presence of increased medium NaCl or sorbitol, H2O2, or ethanol levels significantly suppressed the cot-1 phenotype, restored ion homeostasis, and was accompanied by reduced levels of cyclic AMP-dependent protein kinase (PKA) activity. The cot-1 phenotype could also be partially suppressed by direct inhibition of PKA with KT-5720. A reduced availability of fermentable carbon sources also had a suppressive effect on the cot-1 phenotype. In contrast to the effect of extragenic ropy suppressors of cot-1, environmental stress-related suppression of cot-1 did not change COT1 polypeptide expression patterns in the mutant. We suggest that COT1 function is linked to environmental stress response signaling and that altering PKA activity bypasses the requirement for fully functional COT1.

* Corresponding author. Mailing address: Department of Plant Pathology and Microbiology, Faculty of Agricultural, Food and Environmental Quality Sciences, The Hebrew University of Jerusalem, Rehovot 76100, Israel. Phone: 972-8-9489298. Fax: 972-8-9468785. E-mail: Oded.Yarden{at}huji.ac.il.

Eukaryotic Cell, August 2003, p. 699-707, Vol. 2, No. 4
1535-9778/03/$08.00+0     DOI: 10.1128/EC.2.4.699-707.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.



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