Identification of genes involved in the phosphate metabolism in Cryptococcus neoformans.

Cryptococcus neoformans is a pathogenic basidiomycetous yeast that can cause life-threatening meningoencephalitis in immuno-compromized patients. To propagate in the human body, this organism has to acquire phosphate that functions in cellular signaling pathways and is also an essential component of nucleic acids and phospholipids. Thus it is reasonable to assume that C. neoformans (Cn) possesses a phosphate regulatory system (PHO system) analogous to that of other fungi. By BLAST searches using the amino acid sequences of the components of the PHO system of Saccharomyces cerevisiae (Sc), we found potential counterparts to ScPHO genes in C. neoformans, namely, acid phosphatase (CnPHO2), the cyclin-dependent protein kinase (CDK) inhibitor (CnPHO81), Pho85-cyclin (CnPHO80), and CDK (CnPHO85). Disruption of each candidate gene, except CnPHO85, followed by phenotypic analysis, identified most of the basic components of the CnPHO system. We found that CnPHO85 was essential for the growth of C. neoformans, having regulatory function in the CnPHO system. Genetic screening and ChIP analysis, showed that CnPHO4 encodes a transcription factor that binds to the CnPHO genes in a Pi-dependent manner. By RNA-seq analysis of the wild-type and the regulatory mutants of the CnPHO system, we found C. neoformans genes whose expression is controlled by the regulators of the CnPHO system. Thus the CnPHO system shares many properties with the ScPHO system, but expression of those CnPHO genes that encode regulators is controlled by phosphate starvation, which is not the case in the ScPHO system (except ScPHO81). We also could identify some genes involved in the stress response of the pathogenic yeast, but CnPho4 appeared to be responsible only for phosphate starvation.