A conserved mitogen-activated protein kinase pathway is required for mating in Candida albicans

Candida albicans had been thought to lack a mating process until the recent discovery of a mating type-like locus and mating between MTLa and MTLalpha strains. To elucidate the molecular mechanisms that regulate mating in C. albicans, we examined the function of Cph1 and its upstream mitogen-activated protein (MAP) kinase pathway in mating, as they are homologues of the pheromone-responsive MAP kinase pathway in Saccharomyces cerevisiae. We found that overexpressing CPH1 in MTLa, but not in MTLa/alpha strains, induced the transcription of orthologues of S. cerevisiae pheromone-induced genes and also increased mating efficiency. Furthermore, cph1 and hst7 mutants were completely defective in mating, and cst20 and cek1 mutants showed reduced mating efficiency, as in S. cerevisiae. The partial mating defect in cek1 results from the presence of a functionally redundant MAP kinase, Cek2. CEK2 complemented the mating defect of a fus3 kss1 mutant of S. cerevisiae and was expressed only in MTLa or MTLalpha, but not in MTLa/alpha cell types. Moreover, a cek1 cek2 double mutant was completely defective in mating. Our data suggest that the conserved MAP kinase pathway regulates mating in C. albicans. We also observed that C. albicans mating efficiency was greatly affected by medium composition, indicating the potential involvement of nutrient-sensing pathways in mating in addition to the MAP kinase pathway.