Reprogramming Plants Using Synthetic Signalling Systems

Maintaining food security in today’s rapidly changing agricultural environments necessitates the development of tools to rationally re-design traits that confer productivity and robustness to plants. Plant development and stress response is precisely coordinated, in part, by a chemical circuitry of phytohormones. Their spatiotemporal distribution triggers and tunes developmental and stress-response programs by regulating the expression of key genes. We have developed synthetic hormone activated Cas9-based repressors (HACRs) which allow us alter how these hormone fluxes affect gene regulation. These tools allow us to rewire the phytohormone circuitry, and thereby reprogram plants.

Using auxin responsive HACRs in conjunction with mathematical models of development, we re-engineered the shoot architecture of the model plant, Arabidopsis thaliana. We demonstrate the ability to rationally alter both branching and phyllotaxy in ways that could potentially increase yields if applied to crops. We also used a similar approach to rewire how gibberellic acid regulates plant size and flowering time. In addition to these developmental phenotypes, we also re-engineered how plants respond to stress, specifically insect herbivory. Using a jasmonate responsive HACR were able to link the jasmonate signal produced upon insect herbivory to the regulation genes of interest, creating a pest triggered defense system. This system has the potential to both increase yields by lowering the metabolic load on plants as well as slow down the development of resistance by reducing the environmental exposure to BT.

We are now moving the HACR platform into crop plants, including tomato, maize, and rice, to demonstrate how this approach could be used to create agriculturally useful traits in the feild. We believe these tools and approaches will facilitate the rapid reprogramming of plants for the generation of optimized plant varieties to deal with the agricultural challenges that threaten our future food security.