Nonsex Genes in the Mating Type Locus of Candida albicans Play Roles in a/α Biofilm Formation, Including Impermeability and Fluconazole Resistance

The mating type locus (MTL) of Candida albicans contains the mating type genes and has, therefore, been assumed to play an exclusive role in the mating process. In mating-incompetent a/alpha cells, two of the mating type genes, MTLa1 and MTL alpha 2, encode components of the a1-alpha 2 corepressor that suppresses mating and switching. But the MTL locus of C. albicans also contains three apparently unrelated nonsex genes (NSGs), PIK, PAP and OBP, the first two essential for growth. Since it had been previously demonstrated that deleting either the a/alpha copy of the entire MTL locus, or either MTLa1 or MTL alpha 2, affected virulence, we hypothesized that the NSGs in the MTL locus may also play a role in pathogenesis. Here by mutational analysis, it is demonstrated that both the mating type and nonsex genes in the MTL locus play roles in a/alpha biofilm formation, and that OBP is essential for impermeability and fluconazole resistance.