The award funded by the Systems and Synthetic Biology Program in MCB and the Biotechnology, Biochemical and Biomass Engineering Program in CBET supports research into the auxin signaling system used by plants. Auxin is a hormone present in almost every part of the plant and is essential for diverse cellular responses. However, it remains unclear how each cell in the plant responds to auxin signals differently depending on what type of cell it is, its location, and its history. Understanding how plants use auxin signaling to coordinate multicellular behaviors will shed light on how plants grow and respond to stimuli and may also yield new engineering tools and methods for designing custom cell-cell communication systems. To develop a toolbox for programming multicellular behavior with auxin, key genes will be ported from the auxin sensing pathway in the plant Arabidopsis thaliana into the yeast Saccharomyces cerevisiae. Lab yeast is ideal for the characterization of the pathway because it is easy to manipulate and has all the prerequisites needed to process auxin, but is otherwise essentially insensitive to it. Rigorous quantitative characterization of a large variety of synthetic auxin signaling circuits that mimic those found in plants will be combined with mathematical modeling and engineering design tools to build an understanding of the programmability of the pathway. More broadly, the work may lead to new applications in human tissue engineering and new methods for improving important crop species. The project will also support the development of new undergraduate and K-12 educational modules on synthetic biology and cell signaling that use the auxin/yeast system as an example.
Synthetic cell-cell signaling circuits in yeast will be constructed using genetic parts, pathways, and inspiration from plants. Protein components will be varied across family members to explore how the circuits are tuned. Mathematical modeling and characterization of subtle differences in circuit tunings will elucidate the programmability of the auxin parts. Demonstration of novel cell-cell behaviors will serve as proof of principle of the approach. Specifically, auxin signal processing circuits based on auxin receptors (TIR1, AFB2), transcription factors (ARFs), co-factors (Aux/IAAs) will be constructed. By suitably combining these components, simple signal processing circuits such as filters, repeaters, and pulse generators will be constructed and their dynamic behaviors characterized in yeast. An auxin biosynthesis module, consisting of enzymes that catalyze the production of auxin and controlled by auxin signal processing circuits, will be constructed in yeast to enable a novel mode of cell-cell communication. Auxin sensing circuits will control the production of auxin to achieve signaling functions such as filters and thresholds. The capability to send, receive, and process auxin will enable the investigation of multicellular behaviors such as wave propagation or consensus. The results will not only provide new tools for engineering multicellular systems, but will also provide biological hypotheses about how and why auxin is used so effectively by plants.
