Cell wall perturbation in yeast results in dual phosphorylation of the Slt2/Mpk1 MAP kinase and in an Slt2-mediated increase in FKS2–lacZ expression, glucanase resistance and thermotolerance

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Abstract
The protein kinase C (PKC1) pathway is essential for maintaining cell integrity in yeast. Here it is shown that various forms of cell wall damage result in activation of the downstream MAP kinase Slt2/Mpk1. Several cell wall mutants displayed enhanced FKS2–lacZ expression, a known output of Slt2 activation. A similar response was obtained with wild-type cells grown in the presence of the cell wall perturbants Calcofluor white and Zymolyase. Upregulation of FKS2–lacZ in response to sublethal concentrations of these agents fully depended on the presence of Slt2. The same cell wall stress conditions resulted in dual threonine and tyrosine phosphorylation of Slt2. Both Slt2 phosphorylation and FKS2–lacZ induction could be largely prevented by providing osmotic support to the plasma membrane. Interestingly, Slt2 phosphorylation in response to cell wall damage required the putative plasma-membrane-located sensor Mid2 but not Hcs77/Wsc1. Finally, cell wall perturbation gave rise to cells with increased resistance to glucanase digestion and heat shock. These responses depended on the presence of Slt2. These results indicate that weakening of the cell wall activates the Slt2/Mpk1 MAP kinase pathway and results in compensatory changes in the cell wall.