RIM101-dependent and -independent pathways govern pH responses in Candida albicans

Growth and differentiation of Candida albicans over a broad pH range underl ie its ability to infect an array of tissues in susceptible hosts. We ident ified C. albicans RIM101, RIM20, and RIM8 based on their homology to compon ents of the one known fungal pH response pathway. PCR product-disruption mu tations in each gene cause defects in three responses to alkaline pH: filam entation, induction of PRA1 and PHR1, and repression of PHR2. We find that RIM101 itself is an alkaline-induced gene that also depends on Rim20p and R im8p for induction. Two observations indicate that a novel pH response path way also exists. First, PHR2 becomes an alkaline-induced gene in the absenc e of Rim101p, Rim20p, or Rim8p. Second, we created strains in which Rim101p activity is independent of Rim20p and Rim8p; in these strains, filamentati on remains pH dependent. Thus, pH governs gene expression and cellular diff erentiation in C. albicans through both RIM101-dependent and RIM101-indepen dent pathways.