Systematic Genetic Interaction Analysis Identifies a Transcription Factor Circuit Required for Oropharyngeal Candidiasis

Oropharyngeal candidiasis (OPC) is a common infection that complicates a wide range of medical conditions and can cause either mild or severe disease depending on the patient. The pathobiology of OPC shares many features with candidal biofilms of abiotic surfaces. The transcriptional regulation of C. albicans biofilm formation on abiotic surfaces has been extensively characterized and involves six key transcription factors (Efg1, Ndt80, Rob1, Bcr1, Brg1, and Tec1). To determine if the biofilm transcriptional regulatory network also plays a role in OPC, we carried out a systematic genetic interaction analysis in a mouse model of C. albicans OPC. Whereas each of the six transcription factors are required for biofilm formation, only three homozygous deletion mutants ( ΔΔ, ΔΔ, and ΔΔ) and one heterozygous mutant ( Δ/ ) have reduced infectivity in the mouse model of OPC. Although single mutants (heterozygous or homozygous) of and have no effect on fungal burden, double heterozygous and homozygous mutants have dramatically reduced infectivity, indicating a critical genetic interaction between these two transcription factors during OPC. Using epistasis analysis, we have formulated a genetic circuit, [ + ]→ → , that is required for OPC infectivity and oral epithelial cell endocytosis. Surprisingly, we also found transcription factor mutants with defects in filamentation, such as ΔΔ, ΔΔ, and ΔΔ filament, during oral infection and that reduced filamentation does not correlate with infectivity. Taken together, these data indicate that key biofilm transcription factors are involved in OPC but that the network characteristics and functional connections during infection are distinct from those observed . The pathology of oral candidiasis has features of biofilm formation, a well-studied process . Based on that analogy, we hypothesized that the network of transcription factors that regulates biofilm formation has similarities and differences during oral infection. To test this, we employed the first systematic genetic interaction analysis of C. albicans in a mouse model of oropharyngeal infection. This revealed that the six regulators involved in biofilm formation played roles but that the functional connections between factors were quite distinct. Surprisingly, we also found that while many of the factors are required for filamentation , none of the transcription factor deletion mutants was deficient for this key virulence trait . These observations clearly demonstrate