De novo generation of a phosphate starvation-regulated promoter in Candida glabrata

What steps are required for a promoter to acquire regulation by an environmental condition? We address this question by examining a promoter in Candida glabrata that is regulated by phosphate starvation and the transcription factor Pho4. The gene PMU2 encodes a secreted acid phosphatase that resulted from gene duplication events not present in other Ascomycetes, and only this gene of the three paralogs has acquired Pho4 regulation. We observe that the PMU2 promoter from C. glabrata is not functional in Saccharomyces cerevisiae, which is surprising because it is regulated by Pho4, and Pho4 is regulated in a similar manner in both species - through phosphorylation and localization. Additionally, we determine that phosphate starvation-regulated promoters in C. glabrata do not require the coactivator Pho2, which is essential to the phosphate starvation response in S. cerevisiae. We define a region of the PMU2 promoter that is important for Pho4 regulation, and this promoter region does not contain the canonical CACGTX sequence that ScPho4 utilizes for phosphate starvation-dependent transcription. However, CgPho4 utilizes CACGTX in the CgPHO84 promoter, as mutation of this sequence decreases transcription. We conclude that the acquisition of PMU2 has expanded the binding specificity of CgPho4 relative to ScPho4.