The Vps21 signalling pathway regulates white-opaque switching and mating in <i>Candida albicans</i>

<i>Candida albicans</i> is able to switch between two epigenetic cell types, namely white and opaque. Multiple conserved signalling pathways control the switch between white and opaque cell types in response to environmental changes. Here, we report the regulatory roles of the endosomal Rab family GTPase Vps21 and associated key components of the Vps21 signalling pathway in white-opaque switching and mating in <i>C. albicans</i>. Deletion of <i>VPS21</i> promoted a switch from the white to the opaque phenotype in the presence of N-acetyl-glucosamine (GlcNAc). Consistently, inactivation of the guanine nucleotide exchange factor of Vps21 (Vps9) and downstream components in the Vps21 pathway (Vps3, Vac1, and Pep12) had similar promoting effects on phenotypic switching. The mating efficiency of opaque cells is much higher than that of white cells under standard laboratory culture conditions. However, compared to the wildtype strain, the <i>vps21/vps21</i>, <i>vps9/vps9</i>, <i>vps3/vps3</i>, <i>vac1/vac1</i>, and <i>pep12/pep12</i> mutant strains exhibited dramatically reduced mating efficiencies. Quantitative RT-PCR assays demonstrated that inactivation of the Vps21 signalling pathway led to downregulation of pheromone expression and mating response pathway associated genes. Taken together, our findings indicate that the conserved Vps21 signalling pathway plays critical roles in the regulation of cell-type switching and mating in <i>C. albicans</i>.