Pho4 mediates phosphate acquisition in Candida albicans and is vital for stress resistance and metal homeostasis

During interactions with its mammalian host, the pathogenic yeast Candida albicans is exposed to a range of stresses such as superoxide radicals and cationic fluxes. Unexpectedly, a non-biased screen of transcription factor deletion mutants revealed that the phosphate-responsive transcription factor, Pho4, is vital for the resistance of C. albicans to these diverse stresses. RNA-Seq analysis indicated that Pho4 does not induce stress-protective genes directly. Instead, we show that loss of Pho4 impacts on metal cation toxicity, accumulation, and bioavailability. We demonstrate that pho4Δ cells are sensitive to metal and non-metal cations, and that Pho4-mediated polyphosphate synthesis mediates manganese resistance. Significantly, we show that Pho4 is important for mediating copper bioavailability to support the activity of the copper/zinc superoxide dismutase Sod1, and that loss of Sod1 activity contributes to the superoxide sensitivity of pho4Δ cells. Consistent with the key role of fungal stress responses in countering host phagocytic defences, we also report that C. albicans pho4Δ cells are acutely sensitive to macrophage-mediated killing, and display attenuated virulence in animal infection models. The novel connections between phosphate metabolism, metal homeostasis and superoxide stress resistance, presented in this study, highlights the importance of metabolic adaptation in promoting C. albicans survival in the host.