A Genetic Toggle Switch in Plants

In synthetic biology, genetic components are assembled to make transcriptional units, and transcriptional units are assembled into circuits to perform specific and predictable functions of a genetic device. Genetic devices have been described in bacteria, mammalian cell cultures and small organoids, yet development of programmable genetic circuits for devices in plants has lagged. Programmable genetic devices require defining the components quantitative functions. Because plants have long life spans, studies often use transient analysis to define quantitative functions while verification in stably engineered plants is often neglected and largely unknown. This raises a question if unique attributes of plants such as environmental sensitivity, developmental plasticity, or alternation of generations, adversely impacts predictability of plant genetic circuits and devices. Alternatively, it is also possible that genetic elements to produce predictable genetic devices for plants require rigorous characterization with detailed mathematical modeling. Here we use plant genetic elements with quantitatively characterized transfer functions and developed in silico models to guide their assembly into a genetic device: a toggle switch or a mutually inhibitory gene-regulatory device. Our approach allows computational selection of plant genetic components and iterative refinement of the circuit if the desired genetic functions are not initially achieved. We show that our computationally selected genetic circuit functions as predicted in stably engineered plants including through tissue and organ differentiation. Developing abilities to produce predictable and programmable plant genetic devices opens the prospect of predictably engineering plants unique abilities in sustainable human and environmental systems.