Roles of TUP1 in Switching, Phase Maintenance, and Phase-Specific Gene Expression in Candida albicans

Academic Article


  • ABSTRACT Candida albicans strain WO-1 switches spontaneously and reversibly between a “white” and “opaque” phenotype that affects colony morphology, cellular phenotype, and expression of a number of phase-specific genes and virulence traits. To assess the role of the transcription regulator Tup1p in this phenotypic transition, both TUP1 alleles were deleted in the mutant Δ tup1 . Δ tup1 formed “fuzzy large” colonies made up of cells growing exclusively in the filamentous form. Δ tup1 cells did not undergo the white-opaque transition, but it did switch spontaneously, at high frequency (∼10 −3 ), and unidirectionally through the following sequence of colony (and cellular) phenotypes: “fuzzy large” (primarily hyphae) → “fuzzy small” (primarily pseudohyphae) → “smooth” (primarily budding yeast) → “revertant fuzzy” (primarily pseudohyphae). Northern analysis of white-phase, opaque-phase, and hypha-associated genes demonstrated that Tup1p also plays a role in the regulation of select phase-specific genes and that each variant in the Δ tup1 switching lineage differs in the level of expression of one or more phase-specific and/or hypha-associated genes. Using a rescued Δ tup1 strain, in which TUP1 was placed under the regulation of the inducible MET3 promoter, white- and opaque-phase cells were individually subjected to a regime in which TUP1 was first downregulated and then upregulated. The results of this experiment demonstrated that (i) downregulation of TUP1 led to exclusive filamentous growth in both originally white- and opaque-phase cells; (ii) the white-phase-specific gene WH11 continued to be expressed in TUP1 downregulated cultures originating from white-phase cells, while WH11 expression remained repressed in TUP1 -downregulated cultures originating from opaque-phase cells, suggesting that cells maintained phase identity in the absence of TUP1 expression; and (iii) subsequent upregulation of TUP1 resulted in mass conversion of originally white-phase cells to the opaque phase and maintenance of originally opaque-phase cells in the opaque phase and in the resumption in both cases of switching, suggesting that TUP1 reexpression turns on the switching system in the opaque phase.
  • Authors

    Published In

  • Eukaryotic Cell  Journal
  • Digital Object Identifier (doi)

    Pubmed Id

  • 16373966
  • Author List

  • Zhao R; Lockhart SR; Daniels K; Soll DR
  • Start Page

  • 353
  • End Page

  • 365
  • Volume

  • 1
  • Issue

  • 3