Motility of plant myosins - structure-function relationships

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Although the typical plant cell is immobile due to rigid cell walls, it harbours a highly active intracellular mobility. This mobility is essential because plant cells are very large and have to adjust to a mostly unbuffered environment. A current topic in plant biology is the signal-dependent establishment of cell polarity by directional transport of signalling components. In this context, plant myosins play a pivotal role. Although they share the basic domains with their animal counterparts, they have been found to differ to such a degree that they had to be assigned to separate classes. The fastest intracellular movements known so far are produced by plant myosins. However, neither the structural base for this high motility nor its biological function have been understood so far. Using members from the myosin classes of higher plants (class VIII and XI), we want to investigate the biochemical properties of these motor proteins by in vitro motility assays focussing on velocity and processivity of the movement, time course of ATP-binding and the association with F-actin. Functionality in vivo will be studied by fluorescent fusion constructs transiently transfected into the intact, homologous system. Using plants that are null-mutants for these myosins, we want to assign specific functions to the individual myosin classes. This will contribute to the question whether specific features of the plant-myosin motor domain can be correlated to specific cellular and/or developmental functions.