ABSTRACT: Melanin is an antioxidant polyphenol pigment, which is required for the pathogenicity of many human and plant fungal pathogens. Nevertheless, its comprehensive regulatory mechanism still remain elusive. In this study, we systematically analyzed melanin-regulating signaling pathways in Cryptococcus neoformans. Here we identified four core melanin-regulating TFs, Bzp4, Usv101, Mbs1, and Hob1, which are required for induction of the laccase gene (LAC1). Bzp4, Usv101 and Mbs1 independently regulate LAC1 induction while Hob1 controls Bzp4 and Usv101 expression. Both Bzp4 and Usv101 are translocated from the cytoplasm into the nucleus upon nutrient starved condition, while Mbs1 is constitutively localized in the nucleus. Notably, the cAMP pathway is not involved in regulation of the four TFs, while the HOG pathway negatively regulates induction of BZP4 and LAC1. As potential kinases upstream of the core TFs, we identified the nine core kinases, whose deletion leads to defective melanin production and LAC1 induction. Deletion of GSK3 or KIC1 abolishes induction of LAC1 and BZP4, and also perturbs nuclear translocation of Bzp4. Notably, Gsk3 also regulates the expression of HOB1, USV101, and MBS1, indicating that it is a critical melanin-regulating kinase. Finally, the RNA-sequencing based transcriptome analysis of the wild-type and bzp4Δ, usv101Δ, hob1Δ, and mbs1Δ strains under nutrient rich and starved conditions reveals that the core melanin-regulating TFs govern redundant and distinct classes of genes, which are involved in a variety of biological processes.
