Characterization of the unconventional myosin VIII in plant cells and its localization at the post-cytokinetic cell wall

Myosins are a large superfamily of motor proteins which, in association wit h actin, are involved in intracellular motile processes. In addition to the conventional myosins involved in muscle contractility, there is, in animal cells, a wide range of unconventional myosins implicated in membrane-assoc iated processes, such as vesicle transport and membrane dynamics. In plant cells, however, very little is known about myosins. We have raised an antib ody to the recombinant tail region of Arabidopsis thaliana myosin 1 (a clas s VIII myosin) and used it in immunofluorescence and EM studies on root cel ls from cress and maize. The plant myosin VIII is found to be concentrated at newly formed cross walls at the stage in which the phragmoplast cytoskel eton has depolymerized and the new cell plate is beginning to mature, These walls are rich in plasmodesmata and we show that they are the regions wher e the longitudinal actin cables appear to attach. Myosin VIII appears to be localized in these plasmodesmata and we suggest that this protein is invol ved in maturation of the cell plate and the re-establishment of cytoplasmic actin cables at sites of intercellular communication.