NSF Proposal # IOS-0920747: "The Exocyst and Vesicle Trafficking In Plant Development"
Inside each plant cell, tiny membrane-bound vesicles carry a variety of materials essential for plant growth and development to the plasma membrane, which helps form the cell?s boundary. The mechanism by which these vesicles are delivered to the correct location on the plasma membrane at precisely the right time is not well understood, even though this tight regulation is fundamental to such processes as cell division, cell wall elongation, defense against pathogens, and intercellular communication (e.g., plant hormone signaling). This project will study the role of a particular complex of eight proteins, the exocyst, in such vesicle trafficking. Based upon work in yeast and mammalian systems, the exocyst is hypothesized to work as a tether between a vesicle and its intended location at the plasma membrane, helping to target vesicles to specific sites at developmentally appropriate times. The importance of the exocyst in plants is demonstrated by mutations in exocyst proteins, which cause defective pollen tube growth, reduced stem elongation in the dark, and dwarfism (including short roots). This project will utilize genetic, biochemical, and cell biological methods to more specifically investigate the exocyst?s possible roles in vesicle trafficking, phytohormone signaling, and cytokinesis (cell division), and will examine both pollen tube elongation and primary root growth in the model plant, Arabidopsis thaliana. This work is likely to have broader impacts by informing applied work that seeks to modify plant growth, cell walls (e.g., for biofuels), or pathogen response in agricultural crops. This project will train a postdoctoral researcher and a graduate student, foster a productive collaboration with researchers in the Czech Republic, and provide science outreach to local elementary and high school students.
" Inside each plant cell, microscopic membrane-bound spheres (called vesicles) carry a variety of materials essential for plant growth and development to the plasma membrane and cell wall, which form the cell’s boundary. The mechanism by which these vesicles are delivered to the correct location on the plasma membrane at precisely the right time is not well understood, even though this tight regulation is fundamental to such processes as cell division, cell wall elongation, defense against pathogens, and intercellular communication (e.g., plant hormone signaling). This project helped advance our understanding of this tight control by characterizing the role of the exocyst, a complex of eight proteins, in such vesicle trafficking in the model plant Arabidopsis. Note that the exocyst is conserved and appears to act in all eukaryotes, and thus this work also has implications for fungi, animals and humans. The exocyst is hypothesized to work as a tether between a vesicle and its intended destination at the plasma membrane, helping to target vesicles to specific sites at developmentally appropriate times. This project helped demonstrate that the exocyst plays crucial roles in several different processes in plants that were previously unknown: generation of a fully-developed seed coat cell wall (which presumably helps protect and hydrate the seed upon germination); completion of cytokinesis (i.e., the last step of cell division, required for plant growth); root cell elongation in all dimensions (which helps drive expansion of the root); and proper control of the size of the primary root meristem (the structure in which new cells are generated for growth, and without which, root growth is defective). Due to the clear linkage of the exocyst to key steps in cell growth, this work could have a broader impact by informing applied work that seeks to modify plant growth or cell wall biochemistry (e.g., for biofuels). In addition to these scientific findings, the project also had a significant training, collaboration and outreach component, each with positive outcomes. The project fostered a productive collaboration with researchers in the Czech Republic in the lab of Dr. Viktor ?árský, supporting exchanges of scientists between labs for visits of ~two weeks each year. Not only were these exchanges productive in terms of results in published articles, but they also allowed all members of the Fowler lab (postdocs, graduate students, undergraduates, high school students) to interact directly with researchers from another country, thus enhancing the realization that science is an international enterprise. In addition, the project trained two postdoctoral researchers in high level imaging technologies and phenotypic analysis, allowed an undergraduate researcher the independence to pursue a research project on cell expansion over the course of one summer and two academic years, and provided three other undergraduates with training in basic lab methods (e.g., preparation of DNA from plant samples.) Finally, the outreach component of the project supported participation by three high school interns (through the Apprenticeships in Science and Engineering Program) and one high school science teacher (through the MJ Murdock Charitable Trust’s Partners in Science Program). All three students and the teacher were trained in the technologies and process associated with science and plant biology, and thus have a superb introduction to science and science-related fields as a potential career option, and also have a better understanding of how science investigates our world.
