Higher plants, like their animal counterparts, follow a specific developmental program that leads from a single cell to a complex, functional multicellular organism composed of a myriad of cell types, tissues, and organs. In animals, the interaction of the cytoskeleton-extracellular matrix complex in development, cell morphogenesis and gene expression is well documented, while in plants the exact role comparable proteins (including those of the cell wall and periplasm) play in development and cell morphogenesis has yet to be elucidated. It is likely that cytoskeleton- extracellular matrix proteins in plants will also be found to play a significant and dynamic role in development and morphogenesis. Recently, this investigator has shown that petunia glycine-rich protein 1 (ptGRP1) can be isolated as a member of a large protein complex that is located either in the periplasmic space or just internal to the plasma membrane. Preliminary in vitro translation studies indicate that ptGRP1 possesses a true signal sequence; therefore, it is likely that the ptGRP1 complex is located in the protoplasm. The investigator hypothesizes that it may function as an organizer of the periplasmic space or as a cytoskeleton-cell wall connector. Consistent with this hypothesis, immunocytochemical studies show that the expression of ptGRP1 correlates directly with expansive growth and that this protein is most highly expressed within the vascular system. Moreover, the presence of ptGRP1 antisense RNA results in aberrant development of the plant. Cytological studies show that all ptGRP1 antisense morphological mutants have an inability to form a normal coherent vascular system. In addition, decreased expression of ptGRP1 in these mutants correlates directly with the severity of the mutation. These experiments indicate that normal GRP expression is necessary for correct formation of the vascular system.
