INVESTIGATING THE ROLE OF MYOSIN XI IN CHLOROPLAST PHOTORELOCATION
Daniel MacVeigh-Fierro, Luis Vidali.
Worcester Polytechnic Institute, Worcester, MA.
Understanding how plant cells adapt dynamically to changes in the environment is a fundamental problem of plant biology. Under many conditions, plant cells respond to environmental changes by modifying their intracellular organization. A critical example of intracellular re-organization is chloroplast photo-relocation, which is required for optimal energy harvesting and avoiding photodamage. A key system responsible for the spatial organization of intracellular components is the actin cytoskeleton and its associated motor, myosin XI. We are testing the hypothesis that myosin XI is important for chloroplast photo-relocation. Evaluating this hypothesis has been complicated by the presence of a large myosin XI gene family in vascular plants. As an alternative, we are using the moss Physcomitrella patens as a model system because it only has 2 myosin XI genes. We have developed a moss line expressing only a temperature sensitive allele of myosin XI. With this tool we plan to answer the long-standing question about the participation of myosin XI on chloroplast transport. Because mosses have a conserved, actin-dependent pathway for chloroplast positioning, but also a microtubule dependent system, we have performed control experiments for selectively inhibiting the function of each cytoskeleton. We have also established a reproducible and quantitative assay to evaluate chloroplast photo-relocation. Next, we will quantify chloroplast motility in response to light in myosin XI temperature sensitive and control lines at permissive and restrictive temperatures. Loss of actin-dependent chloroplast motility at the restrictive temperature will support the hypothesis that myosin XI participates in the important process of chloroplast photo-relocation.