Synthetic Gene Networks for 2D Fractal Formation By S. Cerevisiae

Multicellular organisms form patterns to enable new functions and aid in specialization. Here, we link the natural capacity for multicellular growth inherent in Saccharomyces cerevisiae yeast to externally-controlled synthetic gene networks. In response to IPTG and ATc inductions, our engineered S288C yeast can be made to switch between a unicellular lifestyle and the multicellular filamenting patterns usually seen with pseudohyphal growth. Fine-control of dynamic behavior and gene expression within a colony of these cells provides us with the framework for genetic encoding of structural forms, with 2D fractal-like patterns being our goal. We show here how changes in the expression of the BUD gene family can alter the pattern of growth and we link our phenotype switches to genetically-encoded timer circuits in order control the duration that a colony grows either in multicellular or unicellular form. To further our ability to define the 2D fractal we also developed new tools to aid differentiation as a colony grows. We made and characterized new hybrid externally-inducible promoters that only express in mother cells after they have budded a daughter cell. These were designed in order to control how often filaments form new branches in our fractal growth phenotype. These new mother-specific promoters provide a unique type of differentiated regulation that could be applied to other synthetic biology designs where cells within the population diverge to perform alternative tasks.