Three Prevacuolar Compartment Rab GTPases Impact Candida albicans Hyphal Growth

Disruption of vacuolar biogenesis in the pathogenic yeastCandida albicans causes profound defects in polarized hyphal growth. However, the precise vacuolar pathways involved in yeast-hypha differentiation have not been determined. Previously we focused on Vps21p, a Rab GTPase involved in directing vacuolar trafficking through the late endosomalp rev acuolarc ompartment (PVC). Herein, we identify two additional Vps21p-related GTPases, Ypt52p and Ypt53p, that colocalize with Vps21p and can suppress the hyphal defects of thevps21 Δ/Δ mutant. Phenotypic analysis of gene deletion strains revealed that loss of bothVPS21 andYPT52 causes synthetic defects in endocytic trafficking to the vacuole, as well as delivery of the virulence-associated vacuolar membrane protein Mlt1p from the Golgi compartment. Transcription of all three GTPase-encoding genes is increased under hyphal growth conditions, and overexpression of the transcription factor Ume6p is sufficient to increase the transcription of these genes. While only thevps21 Δ/Δ single mutant has hyphal growth defects, these were greatly exacerbated in avps21 Δ/Δypt52 Δ/Δ double mutant. On the basis of relative expression levels and phenotypic analysis of gene deletion strains, Vps21p is the most important of the three GTPases, followed by Ypt52p, while Ypt53p has an only marginal impact onC. albicans physiology. Finally, disruption of a nonendosomal AP-3-dependent vacuolar trafficking pathway in thevps21 Δ/Δypt52 Δ/Δ mutant, further exacerbated the stress and hyphal growth defects. These findings underscore the importance of membrane trafficking through the PVC in sustaining the invasive hyphal growth form ofC. albicans .