RESEARCH-PGR: Dissecting the Genetic Networks Underlying Kranz Anatomy in C4 Grasses

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PI: Thomas Brutnell [Donald Danforth Plant Science Center, (DDPSC)]CoPIs: Elizabeth Kellogg and Todd Mockler (DDPSC), Kimberly Gallagher (University of Pennsylvania), Chris Myers (Cornell University) and Joyce Van Eck (Boyce Thompson Institute for Plant Science)Senior Personnel: Robert Turgeon, Qi Sun, and Klaas van Wijk (Cornell University)Declining yields, increasing population growth and shifting climates are converging to create a perfect storm for agriculture. The looming threats to food security demand transformative innovations in agriculture that will drive the second green revolution. Maize is the most economically important crop in the U.S providing food, feed and bioenergy to the global economy. It is also one of the most photosynthetically productive plants on the planet. This productivity is driven by biochemical and anatomical adaptations associated with C4 photosynthesis. One proposed grand challenge is to introduce C4 traits into C3 crops such as rice and many temperate grasses. A major conceptual breakthrough in the understanding of the development of C4 photosynthesis was realized through the discovery that a root endodermal cell fate module was co-opted to drive a leaf specific cellular differentiation program. Importantly, a prediction from this model suggests that a limited number of changes in genes could lead to a major reprogramming of leaf cell fates. This project will test this prediction and expand on our understanding of the gene regulatory networks that drive both biochemical and anatomical innovations associated with C4 photosynthesis. The results of these studies will not only provide candidate genes for engineering C4 traits into C3 crops, but also provide novel targets for improvement of existing C4 crops such as maize, sugarcane and sorghum. With regard to training and outreach, the project will continue to expand on the MutantMillets outreach program at the DDPSC. MutantMillets provides teaching modules and teaching resources with hands-on activities in the plant sciences to engage high school students in the St. Louis metropolitan region. Importantly, all resources developed through this program will be portable to other school systems through the project website and through the educational networks established by the Education and Outreach Center at the DDPSC. Grasses that utilize C4 photosynthesis include maize, sorghum, sugarcane and Miscanthus. C4 grasses use two distinct cell types to create a CO2 pump that elevates the levels of CO2 in the vicinity of the enzyme Rubisco, effectively eliminating wasteful photorespiration. Under hot, dry conditions C4 systems display significantly increased productivity relative to C3 crops such as rice and wheat. This project aims to identify the foundational genetic and regulatory networks that control the differentiation of the two photosynthetic cell types in maize - the bundle sheath (BS) and mesophyll (M). This work expands on recent discoveries that has linked the SHR/SCR/IDD regulatory module to the differentiation of the BS and M cells of maize and provides new opportunities to more fully explore the function of this regulatory network in C4 grasses through an integrated systems biology approach. These studies will include the development and implementation of several emerging technologies including cell-type specific proteomics, CRISPR/Cas9 gene editing technologies, robotics-based yeast one hybrid screens, ChIP-seq, translatomics, X-ray computed tomography, novel informatics/network analysis algorithms, and modeling of both developmental phenotypes and mechanistic regulatory networks. All data and resources generated in this project will be made accessible to the public through the project website and through long-term repositories.