Mechanistic Insights Into Chloroplast FtsZ Assembly and Dynamics

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Plants possess specialized compartments called chloroplasts that allow them to harvest light energy directly from the sun and convert it to chemical energy through the process of photosynthesis. Photosynthesis produces the organic compounds that comprise the base of the global food chain and are crucial for agricultural production. As plant cells expand during leaf growth, their chloroplast numbers increase dramatically through the process of division, which is crucial for increasing photosynthetic capacity. Consistent with their cyanobacterial origin, chloroplasts inherited several components of their division machinery from the cell division machinery in their prokaryotic ancestors. Foremost among these is a cytoskeletal protein called FtsZ. In both bacteria and chloroplasts, FtsZ proteins assemble into polymers that form a ring, called the "Z ring", at the center of the cell or organelle that contributes to the constrictive force driving the division process. This project seeks insight into how chloroplasts use these proteins in division and seeks a better understanding of the differences between chloroplast and prokaryotic division. Broader Impact activities will include participation in the Michigan State University Girl Scout STEM Demo Day, which provides hands-on demonstrations and activities to girls from across the state. Also, a post-doc will be involved in updating and expanding the Wikipedia page on chloroplast biology to help the general public better understand how chloroplasts work.Whereas bacterial cell division requires only a single type of FtsZ, chloroplast division requires two functionally distinct types of FtsZ that copolymerize. Previous studies based largely on the FtsZ proteins from a model plant species have led to the hypothesis that their copolymerization enhances polymer rearrangements (dynamics) within the Z ring, which is essential for Z-ring constriction. This project focuses on understanding in greater mechanistic detail how FtsZ pairs cooperate not only in plants, but also in algae, to carry out chloroplast division. Experimental approaches will include analysis of the dynamics of Z rings reconstituted in yeast by fluorescence imaging, a suite of in vitro assembly and biochemical assays, computational modeling to better understand how FtsZ pairs interact in polymers, and advanced microscopy techniques to investigate how the two FtsZs are arranged in polymers. As copolymerization represents a novel and important variation on Z-ring function unique to chloroplasts, study of FtsZ pairs will contribute to broader understanding of the diversity of FtsZ-mediated division systems.