Grf10 Transcription Factor Coordinates Nutrient Assimilation, Metabolism and Morphogenesis in Candida albicans
Rolfes, Ronda J.
Candida albicans is a commensal of the human microbiome and a major human fungal pathogen. Morphogenesis and metabolism are key attributes that allow C. albicans to thrive and infect the human host. Grf10, a homeodomain-containing transcription factor, regulates both morphogenesis and metabolism in C. albicans. The grf10∆ mutants were defective in yeast-to-hyphal transition, chlamydospore and biofilm formation, and also showed dramatically attenuated virulence in a mouse of infection model. Overexpression of GRF10 led to filamentation under yeast-promoting growth conditions, consistent with upregulation of GRF10 levels during hyphal growth and biofilm formation. Additionally, Grf10 and Bas1, a myb-containing transcription factor, are required for full upregulation of adenylate biosynthesis (ADE genes), one-carbon metabolism, and a nucleoside permease (NUP gene) when C. albicans is grown under adenine limitation. Phenotypic analysis revealed that the grf10∆ and bas1∆ mutants exhibited growth defects when grown in the absence of adenine. Unlike the strong morphological effects associated with the grf10∆ mutant, the bas1∆ mutant showed only modest filamentation defects and weak attenuated virulence.Differences in behavior of Grf10 and Bas1 in morphogenesis led to hypothesis that Grf10 independently regulates morphogenesis and metabolism. To test this hypothesis, the ability of LexA-GRF10 overexpression to drive filamentation was examined in the absence of Bas1 and adenine. The results showed that filamentation produced by LexA-Grf10 overexpression is independent from Bas1 and adenine levels. Alanine substitution analysis revealed that Grf10 required its own DNA-binding homeodomain to trigger hyphal growth. Thus, Grf10 separately regulates filamentation and adenine responsive genes.In addition, RNA-seq analysis demonstrated that Grf10 was required for expression of many genes involved with nutrient assimilation such as inorganic phosphate, copper, and iron. Phenotypic analysis revealed that the grf10∆ mutant was resistant to copper toxicity and prolonged exposure to excess copper triggered hyphal growth in this mutant. Importantly, key residues D302 and E305, predicted to be important for protein-protein interactions, are required for Grf10 functions during the adenine starvation, the filamentation, and copper toxicity responses. Together, these results suggest a model that Grf10 regulates target genes in multiple pathways by interacting with different protein partners.
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