Interaction of Plant Cell Surface Macromolecules and Controlof Cell Expansion

本研究的长期目标是确定植物细胞表面蛋白在细胞分化和植物形态发生中的功能，并研究这些功能的潜在分子和细胞生物学基础。质膜阿拉伯半乳糖蛋白（AGPs）是一个丰富的蛋白聚糖家族，被认为与细胞骨架和细胞壁相互作用。经β - d -葡萄糖基Yariv抗原（一种选择性结合AGPs的小配体）处理的拟南芥植株出现了reb（根表皮膨大）突变体，其表现为根表皮细胞膨大、根生长减少和根明显弯曲。这一发现首次有力地提示了细胞表面AGPs在控制细胞增殖方向和根发育中的作用，并预测了reb突变体的根中含有缺陷的AGPs。为了验证这一假设，将进一步研究Yariv抗原处理对拟南芥根系发育的影响。用交叉电泳和免疫组织化学分析reb突变体的AGPs。为了了解AGP功能的潜在机制，将采用几种新方法来表征AGP与其他细胞表面大分子之间的相互作用。此外，β - d -glucosyl Yariv抗原不敏感的拟南芥突变体将被分离和表征。这些突变体将有助于鉴定控制AGPs与其细胞表面配体之间相互作用的位点。这种综合的生化、分子和遗传方法将使我们能够牢固地建立细胞表面AGPs在控制细胞扩增和根发育中的作用，并使我们更好地理解这种功能的潜在分子和细胞生物学机制。

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.