Optogenetic Control of Phosphate-Responsive Genes Using Single-Component Fusion Proteins in <i>Saccharomyces cerevisiae</i>

Blue light illumination can be detected by light-oxygen-voltage (LOV) photosensing proteins and translated into a range of biochemical responses, facilitating the generation of novel optogenetic tools to control cellular function. Here, we develop new variants of our previously described VP-EL222 light-dependent transcription factor and apply them to study the phosphate-responsive signaling (<i>PHO</i>) pathway in the budding yeast <i>Saccharomyces cerevisiae</i>, exemplifying the utilities of these new tools. Focusing first on the VP-EL222 protein itself, we quantified the tunability of gene expression as a function of light intensity and duration and demonstrated that this system can tolerate the addition of substantially larger effector domains without impacting function. We further demonstrated the utility of several EL222-driven transcriptional controllers in both plasmid and genomic settings, using the <i>PHO5</i> and <i>PHO84</i> promoters in their native chromosomal contexts as examples. These studies highlight the utility of light-controlled gene activation using EL222 tethered to either artificial transcription domains or yeast activator proteins (Pho4). Similarly, we demonstrate the ability to optogenetically repress gene expression with EL222 fused to the yeast Ume6 protein. We finally investigated the effects of moving EL222 recruitment sites to different locations within the <i>PHO5</i> and <i>PHO84</i> promoters, as well as determining how this artificial light-controlled regulation could be integrated with the native controls dependent on inorganic phosphate (P_i) availability. Taken together, our work expands the applicability of these versatile optogenetic tools in the types of functionalities that they can deliver and the biological questions that can be probed.