Recognition of galactose by a scaffold protein recruits a transcriptional activator for the <i>GAL</i> regulon induction in <i>Candida albicans</i>.

Abstract

The <i>GAL</i> pathway of yeasts has long served as a model system for understanding of how regulatory mode of eukaryotic metabolic pathways evolves. While Gal4 mode has been well-characterized in Saccharomycetaceae clade, little is known about the regulation of the <i>GAL</i> pathway in other yeasts. Here, we find that Rep1, a Ndt80-like family transcription factor, serves as a galactose sensor in the commensal-pathogenic fungus <i>Candida albicans</i>. It is presented at the <i>GAL</i> gene promoters independent of the presence of galactose. Rep1 recognizes galactose via a direct physical interaction. The net result of this interaction is the recruitment of a transcriptional activator Cga1 (Candida galactose gene activator, orf19.4959) and transcription of the <i>GAL</i> genes proceeds. Rep1 and Cga1 are conserved across the CTG species. Rep1 itself does not possess transcriptional activity. Instead, it provides a scaffold to recruit different factors for transcriptional regulation. Rep1-Cga1 mode of regulation represents a new example of network rewiring in fungi, which provides insight into how <i>C. albicans</i> evolves transcriptional programs to colonize diverse host niches.