Synthetic Morphogenesis in Plant Roots

Form often dictates function in biological systems and humans have played significant roles in shaping plants and animals to suit specific needs. Notable examples include dwarf rice and wheat crops, which increase grain yield at the expense of straw biomass, and dachshunds, whose long bodies can flush out burrow-dwelling animals for hunters. These examples illustrate how allometric changes in relative dimensions of growth can have profound effects. Progress in engineering the form of multicellular organisms has been limited by our capacity to design genetic programs that rearrange cell types and organs in a predictable manner. Development is more complicated than other biological processes already engineered by humans, e.g., metabolism, because it is hierarchical and governed by a small number of versatile signaling molecules. These features of development make it difficult to change one aspect of an organisms' structure without affecting others. Fortunately, the diversity of biological forms on earth suggests that several structural features can be altered independently. We are building synthetic gene circuits to control development in the model plant Arabidopsis thaliana. Three morphogenic parameters, growth rate, growth angle, and branching rate, are being altered in roots to test our ability to control developmental processes independently. Roots are used as a model system because they are structurally simple and their form is directly linked to function. Root systems that are broad and shallow can quickly absorb nutrients from the soil, whereas deep root systems can help plants obtain water during drought. Like other plant organs, roots possess a basic structure that is defined by a genetically encoded program. In a standardized the environment, roots development can serve as an excellent model for engineering biological form. Here, we use a model of root growth to guide the design of synthetic root structures. The model simulates basic processes in root development, e.g. elongation, branching, and is used to identify processes affected by over expression of developmental genes in specific root tissues.