Bistable Genetic Switch Design in Plant System

Programming the behavior of biological traits using rationally designed genetic devices has been the goal of synthetic biology. Genetic switches are one of the devices essential for decision making at different phases of regulatory networks and allow programmable control over biological systems. To build robust biological based bistable switches, orthogonal genetic components and quantitatively determined input-output functions are vital. Here, we are reporting the characterization of genetic parts and the demonstration of a synthetic genetic toggle switch design in complex plant system. The circuit uses synthetic repressor-repressible promoter pairs that are quantitatively balanced and can be controlled by external inducers to toggle between two stable output states (ON vs. OFF). We have designed and quantitatively characterized the behavior of a series of these pairs transiently in protoplasts. The kinetic parameters derived from these assays were used to guide the design of more complex genetic circuits for whole plant. So far, homozygous transgenic lines containing bistable genetic circuits are generated and showed reasonable toggle switch behavior under the control of external inputs. By modifying the output of these toggle switches, we hope to increase the engineering potential of useful plant traits.