Motor Protein Myo5p Is Required To Maintain the Regulatory Circuit ControllingWOR1Expression in Candida albicans
ABSTRACTTheCandida albicans MYO5gene encodes myosin I, a protein required for the formation of germ tubes and true hyphae. Because the polarized growth of opaque-phase cells in response to pheromone results in mating projections that can resemble germ tubes, we examined the role of Myo5p in this process. We localized green fluorescent protein (GFP)-tagged Myo5p in opaque-phase cells ofC. albicansduring both bud and shmoo formation. In vegetatively growing opaque cells, Myo5p is found at sites of bud emergence and bud growth, while in pheromone-stimulated cells, Myo5p localizes at the growing tips of shmoos. Intriguingly, cells homozygous forMTLain which theMYO5gene was deleted failed to switch efficiently from the white phase to the opaque phase, although ectopic expression ofWOR1from theMET3promoter can convertmyo5mutants into mating-competent opaque cells. However, whenWOR1expression was shut off, themyo5-defective cells rapidly lost both their opaque phenotype and mating competence, suggesting that Myo5p is involved in the maintenance of the opaque state. WhenMYO5is expressed conditionally in opaque cells, the opaque phenotype, as well as the mating ability of the cells, becomes unstable under repressive conditions, and quantitative real-time PCR demonstrated that the shutoff ofMYO5expression correlates with a dramatic reduction inWOR1expression. It appears that while myosin I is not directly required for mating inC. albicans, it is involved inWOR1expression and the white-opaque transition and thus is indirectly implicated in mating.