CAREER: Role of Plant Myosin XI in Polarized Secretion and Actin Dynamics

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Understanding the fundamental mechanisms that govern polarized plant cell growth is an important unsolved problem in biology that is critical for future development of plants with improved growth characteristics. Polarized plant cell growth is a highly focused type of growth essential for land colonization, sexual reproduction, and water and nutrient uptake. A central player in the regulation of polarized cell growth is the actin cytoskeleton, an evolutionarily conserved assembly of dynamic nano-polymers (actin filaments) and nano-motors (myosins). The actin cytoskeleton is known to participate in the organization of components inside the cell, including endomembranes and secretory vesicles containing materials important for cell growth. The long-term goal of the research is to understand how the actin cytoskeleton and endomembrane compartments interact to generate polarized plant cell growth. Toward accomplishing this goal, the objective of the project is to determine the role of the motor myosin XI in the coordination between actin filaments, endomembranes, and polarized secretion of growth materials. The central hypothesis is that membrane compartments, such as secretory vesicles, function as active centers of organization where actin polymerization and myosin XI-based transport cooperate to produce polarized secretion. The following three specific aims are designed to test the central hypothesis using the moss Physcomitrella patens as a plant model system: 1) identify the membrane compartments associated with myosin XI; 2) identify the receptors that anchor myosin XI to its membrane cargo; and 3) determine how myosin XI, actin polymerization, and endomembranes cooperate to regulate the organization of the actin cytoskeleton during polarized cell growth. The project will investigate a novel mechanism for polarized secretion based on the cooperation of myosin XI and actin polymerization using unique genetic tools developed to reduce overall myosin XI activity or only its cargo binding activity. The research provides a viable model for cell polarization driven by the concerted action of endomembrane compartments, myosin XI, and a dynamic actin cytoskeleton. Broader Impacts. In addition to contributing to the basic understanding of biology, the knowledge obtained from this project has the potential to identify strategies to improve plant reproduction, plant fitness, and plant growth. These improvements can impact agricultural science by promoting the development of plants with characteristics necessary for a more sustainable future. From an educational perspective, the project impacts the rapidly advancing field of biology where there is an increasing need for microscopy and imaging education and training. In order to integrate these disciplines within the general biology curriculum, a new microscopy and imaging course will be implemented. The goal of the laboratory and inquiry-based course is to train students to apply microscopy in research both in class and as part of independent research projects. The new course will have a modular format that allows the use of some of its parts for outreach programs. The project also provides opportunities for improving presentation and networking skills during the postdoctoral experience through the continued development of a social networking tool (LectureBank.org) for postdoctoral scholars with an emphasis on underrepresented minority life scientists. The tool serves as a peer-to-peer mentoring resource and provides a forum for sharing materials and experiences.