Developing A Genetic Toggle Switch in Arabidopsis

Plant synthetic biology has significant technological potential, but the complexity of plant biology has made it difficult to engineer complex information-processing circuits into plants. The synthetic genetic toggle switch, which translates binary external stimuli into binary internal outcomes, was the earliest information-processing synthetic circuit developed in E. Coli in 2000. Here we report on results from a long collaborative effort to develop the first synthetic toggle switch in Arabidopsis. We used a forward engineering approach by first analyzing synthetically designed repressors in plant protoplasts[1]. Parameters obtained allowed us to predict the combinations most likely to work in the plant. We then chose two combinations to test, assembled and inserted them in Arabidopsis and used luciferase luminescence to report on circuit behavior. Assessing circuit behavior in plants was affected by unexpected phenomena such as tissue specific differences and the confounding effects of plant growth. Despite these issues we were able to successfully fit a mathematical model to the plant data using MCMC sampling. Analysis of the results led to the conclusion that one of the two combinations satisfied the tests for bistability. This circuit is, to our knowledge, the first synthetic genetic toggle switch in a plant[2].