9507191 Zhu The long-term objectives of this research are to determine the functions of plant cell surface proteins in cell differentiation and plant morphogenesis, and to study the underlying molecular and cell biological basis of such functions. Plasma membrane arabinogalactan-proteins (AGPs) are a family of abundant proteoglycans that are thought to interact with both the cytoskeleton and cell wall. Arabidopsis plants treated with Beta-D-glucosyl Yariv antigen (a small ligand that selectively binds AGPs), phenocopy the reb (root epidermal bulger) mutants which display root epidermal cell bulging, reduced root growth and sharp root bending. This observation strongly suggests for the first time a role of cell surface AGPs in the control of direction of cell expansion and root development, and predicts that the reb mutants contain defective AGPs in the root. To test this hypothesis, studies will be carried out to further examine the effect of Yariv antigen treatment on Arabidopsis root development. AGPs in reb mutants will be analyzed using crossed electrophoresis and immuno- histochemistry. To understand the underlying mechanisms of AGP function, several novel approaches will be employed to characterize the interactions between AGPs and other cell surface macromolecules. Furthermore, Beta-D-glucosyl Yariv antigen-insensitive Arabidopsis mutants will be isolated and characterized. The mutants will be useful in identifying loci that control the interaction between AGPs and their cell surface ligands. This integrated biochemical, molecular, and genetic approach will enable us to firmly establish a role for cell surface AGPs in the control of cell expansion and root development, and allow a better understanding of the underlying molecular and cell biological mechanisms for such a function.
