Activation of the cell wall integrity pathway promotes escape from G2 in the fungus Ustilago maydis

• Published in: PLoS genetics Vol. 6; no. 7; p. e1001009
• Main Authors: Carbo, Natalia, Perez-Martin, Jose
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 01.07.2010; Public Library of Science (PLoS)
• Subjects: Bacterial cell walls; cdc25 Phosphatases - genetics; cdc25 Phosphatases - metabolism; Cell Biology/Cell Signaling; Cell Biology/Microbial Growth and Development; Cell cycle; Cell Wall - enzymology; Cell Wall - genetics; Cell Wall - metabolism; Developmental Biology/Microbial Growth and Development; Extracellular signal-regulated kinases; Fungal Proteins - genetics; Fungal Proteins - metabolism; G2 Phase; Kinases; MAP Kinase Signaling System; Microbiology/Microbial Growth and Development; Mitogen-Activated Protein Kinases - genetics; Mitogen-Activated Protein Kinases - metabolism; Phosphorylation; Physiological aspects; Proteins; Saccharomyces cerevisiae; Schizosaccharomyces pombe; Ustilago - cytology; Ustilago - enzymology; Ustilago - genetics; Ustilago - metabolism; Ustilago maydis; Yeast; Yeast fungi; Spain
• ISSN: 1553-7404; 1553-7390; 1553-7404
• DOI: 10.1371/journal.pgen.1001009

It is widely accepted that MAPK activation in budding and fission yeasts is often associated with negative effects on cell cycle progression, resulting in delay or arrest at a specific stage in the cell cycle, thereby enabling cells to adapt to changing environmental conditions. For instance, activation of the Cell Wall Integrity (CWI) pathway in the budding yeast Saccharomyces cerevisiae signals an increase in CDK inhibitory phosphorylation, which leads cells to remain in the G2 phase. Here we characterized the CWI pathway of Ustilago maydis, a fungus evolutionarily distant from budding and fission yeasts, and show that activation of the CWI pathway forces cells to escape from G2 phase. In spite of these disparate cell cycle responses in S. cerevisiae and U. maydis, the CWI pathway in both organisms appears to respond to the same class cell wall stressors. To understand the basis of such a difference, we studied the mechanism behind the U. maydis response. We found that activation of CWI pathway in U. maydis results in a decrease in CDK inhibitory phosphorylation, which depends on the mitotic phosphatase Cdc25. Moreover, in response to activation of the CWI pathway, Cdc25 accumulates in the nucleus, providing a likely explanation for the increase in the unphosphorylated form of CDK. We also found that the extended N-terminal domain of Cdc25, which is dispensable under normal growth conditions, is required for this G2 escape as well as for resistance to cell wall stressors. We propose that the process of cell cycle adaptation to cell stress evolved differently in these two divergent organisms so that each can move towards a cell cycle phase most appropriate for responding to the environmental signals encountered.