Plants build cells in a diverse range of shapes that are important both for specialized cell function and for creating the structure of the plant itself. To create these shapes, plant cells must organize the molecular structure and mechanical properties of the rigid walls that encase them. A highly ordered network of protein polymers known as the cortical microtubule cytoskeleton is employed to organize cell walls and to build specific cell shapes. The cortical microtubule cytoskeleton has been shown to (1) guide the trajectories of cellulose synthase complexes as they deposit cellulose, the major structural component of the cell wall; (2) position the delivery of these complexes to their sites of action at the cell membrane; and (3) tether trafficking organelles containing cellulose synthase in the cortex of the cell during conditions of stress. The molecular mechanisms by which the microtubule cytoskeleton carries out these activities are not known, and the precise biological functions of all these processes in cell growth and morphogenesis are not well understood. To investigate these questions the Ehrhardt lab designed a genetic screen for mutants that are defective in trafficking of cellulose synthase and its organization at the cell cortex and cell membrane. This screen revealed a class of mutants that are defective in CSC guidance and have lost cortical tethering, the lost mutants. These mutants are exciting tools to discover new molecules involved in cytoskeletal function, and to get new insight into the network of interactions that organize the cell wall. This project has three major experimental aims: (1) to investigate LOST function by characterizing these mutants at the levels of subcellular protein and organelle dynamics, cell and tissue growth, and cell wall structure; (2) to identify these genes and determine where the protein products reside in the cell and how they behave, and (3) to identify other proteins that interact with LOST proteins to build a molecular interaction and/or regulatory network from the microtubule cytoskeleton to the cell wall biosynthetic machinery. These studies will provide new insight into several central questions in plant cell biology: the function of the cortical cytoskeleton, the mechanisms of cell morphogenesis, and the mechanisms for biosynthesis and organization of cellulose and the cell wall - major targets of biofuel and biomaterials research.
Broader Impacts. Integrating research and education. The research activities in this project will contribute to the training of a young post doctoral scientist and will give several high school students first hand exposure to basic research. These students will participate in the Carnegie Summer Internship Program, enhancing the student's experience through weekly research talks by Carnegie faculty and researchers and by giving them an opportunity to present their findings in a pubic forum. Materials from this research will be used in Stanford's Advanced Imaging Course. This course gives students hands on experience in building advanced instruments like laser traps and TIRF microscopes. Training of under represented groups in science. Summer research assistants will be recruited from local high schools with substantial minority representation. Other outreach activities include establishing collaborations with researchers in departments and institutions that only train undergraduates. Communication of research. Research results will be incorporated into the Ehrhardt lab website, deepgreen.stanford.edu. This site is used for class instruction at several universities around the world. Images and results from the lab have previously been incorporated into major textbooks. Infrastructure development. The Ehrhardt lab has generated a database of fluorescent protein markers for plant cells and the associated molecular resources. Materials generated by this research will be added to this database and distributed by the lab's website and by the Arabidopsis stock center. Other societal benefits. Cellulose provides the basis for mechanical support of terrestrial plant life and is the major sink for photosynthetic output. The molecular mechanisms that govern cellulose biosynthesis and cell wall organization have relevance for crop improvement, engineering of biomaterials, and biofuel development.
