Plants as Self-Sustaining Platforms for Synthetic Biology

Plant synthetic biology promises immense technological benefits, including the potential development of a sustainable bio-based economy. This goal will require the ability to design and produce synthetic gene circuits with predictable outputs. Such circuits are built from quantitatively characterized genetic parts, but can be slow in plants due to the time required for stable transformation. We have developed a method for rapid characterization of parts using transient expression in protoplasts and dual luciferase outputs. Using this method, we characterized hundreds of quantitatively characterized synthetic parts. We also developed descriptive models and normalization methods to account for stochastic effects. Our approach will speed the development of well-characterized genetic parts that can then be modeled, assembled and transferred to plants to produce predictable functions and controls such as toggle switches and positive feedback circuits. Another type of circuit is an environmental biosensor that enables a plant to detect a small molecule such as digoxin and initiate a transcriptional response. A transcriptional activator was fused to a computationally designed ligand binding domain; the fusion is unstable and inactive unless in the presence of digoxin. Upon binding the ligand, the activator activates transcription of a reporter or gene of interest. Such circuits can be precisely tuned through mathematical modeling and incorporating well-characterized and well-balanced parts, and can be used to control expression of desirable traits or the production of materials in plants.