Candida albicans is an opportunistic, dimorphic fungus that causes can-didiasis in immunocompromised people. C. albicans forms specialized structures called microcolonies that are important for surface adhesion and virulence. Microcolonies form in response to specific environmental conditions and require glycolytic substrates for optimal growth. However, fungal signaling pathways involved in sensing and transmitting these environmental cues to induce microcolony formation have not been identified. Here, we show that the C. albicans Ras1-cAMP cascade is required for microcolony formation, while the Cek1-MAP kinase pathway is not required, and Hog1 represses microcolony formation. The membrane protein Sho1, known to regulate the Cek1 pathway in yeasts, was indispensable for C. albicans mi-crocolony formation but regulated the Ras1-cAMP pathway instead, based upon diminished intracellular levels of cAMP and reduced expression of core microcolony genes, including HWP1, PGA10, and ECE1, in C. albicans sho1Δ cells. Based upon predicted physical interactions between Sho1 and the glycolytic enzymes Pfk1, Fba1, Pgk1, and Cdc19, we hypothesized that Sho1 regulates Ras1-cAMP by establishing cellular energy levels produced by glycolysis. Indeed, microcolony formation was restored in C. albicans sho1Δ cells by addition of exogenous intermediates of glycoly-sis, including downstream products of each predicted interacting enzyme (fructose 1,6 bisphosphate, glyceraldehyde phosphate, 3-phosphoglyceric acid, and pyruvate). Thus, C. albicans Sho1 is an upstream regulator of the Ras1-cAMP signaling pathway that connects glycolytic metabolism to the formation of pathogenic microcolonies.
- Candida albicans