A functional analysis of the exocyst subunit Sec15 in Candida albicans. Academic Article uri icon

abstract

  • In prior studies of exocyst-mediated late secretion in Candida albicans, we have determined that Sec6 contributes to cell wall integrity, secretion, and filamentation. A conditional mutant lacking SEC6 expression exhibits markedly reduced lateral hyphal branching. In addition, lack of the related t-SNAREs Sso2 and Sec9 also leads to defects in secretion and filamentation. To further understand the role of the exocyst in the fundamental processes of polarized secretion and filamentation in C. albicans, we studied the exocyst subunit Sec15. Since Saccharomyces cerevisiae SEC15 is essential for viability, we generated a C. albicans conditional mutant strain in which SEC15 was placed under the control of a tetracycline-regulated promoter. In the repressed state, cell death occurred after 5 hours in the tetR-SEC15 strain. Prior to this timepoint, the tetR-SEC15 mutant was markedly defective in Sap and lipase secretion, and demonstrated increased sensitivity to zymolyase and chitinase. Notably, tetR-SEC15 mutant hyphae were characterized by a hyper-branching phenotype, in direct contrast to strain tetR-SEC6 which had minimal lateral branching. We further studied localization of the Spitzenkörper, polarisome, and exocyst in the tetR-SEC15 and tetR-SEC6 mutants during filamentation. Mlc1-GFP (marking the Spitzenkörper), Spa2-GFP (the polarisome) and Exo70-GFP (exocyst) localization was normal in the tetR-SEC6 mutant, whereas these structures were mislocalized in the tetR-SEC15 mutant. Following alleviation of gene repression by removing doxycycline, first Spitzenkörper, then polarisome and finally exocyst localization were recovered sequentially. These results indicate that the exocyst subunits Sec15 and Sec6 have distinct roles in mediating polarized secretion and filamentation in C. albicans.Copyright © 2015, American Society for Microbiology. All Rights Reserved.

publication date

  • October 2015