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Transcript Profiles of Candida albicans Cortical Actin Patch Mutants Reflect Their Cellular Defects: Contribution of the Hog1p and Mkc1p Signaling Pathways

Biotechnology Research Institute, National Research Council of Canada, 6100 Royalmount, Montreal H4P 2R2, Quebec, Canada,¹ Department of Genetics, Cell Biology & Development, University of Minnesota, 6-160 Jackson Hall, 321 Church St. SE, Minneapolis, Minnesota 55455²

Received 23 December 2005/ Accepted 14 June 2006

In Candida albicans, Myo5p and Sla2p are required for the polarized localization and function of cortical actin patches, for hyphal formation, and for endocytosis. Deletion of either the MYO5 or the SLA2 gene generated a common transcriptional response that involved changes in the transcript levels of cell wall protein- and membrane protein-encoding genes. However, these profiles were distinct from those observed for a mutant with specific deletions of the actin-organizing domains of Myo5p or for wild-type cells treated with cytochalasin A, both of which also generate defects in the organization of cortical actin patches. The profiles observed for the myo5 and sla2 mutants had similarities to those of wild-type cells subjected to an osmotic shock, and the defects in cortical patch function found with myo5 and sla2 mutants, but not cortical actin patch distribution per se, affected sensitivity to various stresses, including heat and osmotic shocks and cell wall damage. Secondary effects coupled with defective endocytosis, such as lack of polarized lipid rafts and associated protein Rvs167-GFP (where GFP is green fluorescent protein) and lack of polarized wall remodeling protein GFP-Gsc1, were also observed for the myo5 and sla2 mutants. The mitogen-activated protein kinases Hog1p and Mkc1p, which mediate signaling in response to osmotic stress and cell wall damage, do not play a major role in regulating the transcript level changes in the myo5 and sla2 mutants. Hog1p was not hyperphosphorylated in the myo5 and sla2 mutants, and the transcript levels of only a subset of genes affected in the myo5 mutant were dependent upon the presence of Hog1p and Mkc1p. However, it appears that Hog1p and Mkc1p play important roles in the myo5 mutant cells because double deletion of myosin I and either Hog1p or Mkc1p resulted in very-slow-growing cells.

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