Three Prevacuolar Compartment Rab GTPases Impact Candida albicans Hyphal Growth

Disruption of vacuolar biogenesis in the pathogenic yeast Candida albicans causes profound defects in polarized hyphal growth. However, the precise vacuolar pathways involved in yeast-hypha differentiation have not been determined. Previously we fo-cused on Vps21p, a Rab GTPase involved in directing vacuolar trafficking through the late endosomal prevacuolar compartment (PVC). Herein, we identify two additional Vps21p-related GTPases, Ypt52p and Ypt53p, that colocalize with Vps21p and can suppress the hyphal defects of the vps21/mutant. Phenotypic analysis of gene deletion strains revealed that loss of both VPS21 and YPT52 causes synthetic defects in endocytic trafficking to the vacuole, as well as delivery of the virulence-associated vacuolar membrane proteinMlt1p 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 the vps21/ single mutant has hyphal growth defects, these were greatly exacerbated in a vps21/ ypt52/ 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 on C. albicans physiol-ogy. Finally, disruption of a nonendosomal AP-3-dependent vacuolar trafficking pathway in the vps21/ ypt52/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 of C. albicans. The fungal vacuole plays a vital role in supporting the pathoge-nicity of Candida albicans and Cryptococcus neoformans (1–3