This proposal outlines experiments to characterize a recently identified protein that appears to be directly involved in the induction of plant cell wall expansion. The protein will be purified in quantities sufficient to raise rabbit polyclonal antibodies. The antibodies will be used (i) to identify the anatomical and cytological location of the protein, (ii) to quantify developmental changes in the protein, and (iii) to test whether this or homologous proteins are involved in growth of other organs and other species. The purified protein will be assayed for enzymatic activities and binding properties that might provide clues about the biochemical mechanism of its wall-extension activity. Cell walls will also be analyzed for evidence of post-translational modification (e.g. thiolreduction or protein phosphorylation) of this or other proteins, under the influence of auxin and other growth-control agents. The results will test the hypothesis that plant cell expansion is developmentally regulated by this protein, which appears to be the first endogenous protein shown to cause expansion of isolated plant cell walls. The growth of plants is controlled primarily by the relaxation and expansion of the polymeric wall. The precise molecular structure of the plant cell wall and the molecular mechanism of cell wall relaxation and expansion is not known. The identification of a specific protein that can induce these processes in isolated cell walls provides strong evidence that the protein is directly involved in this phenomenon. The purification and characterization provides for the first time the ability to directly investigate the molecular mechanism of cell enlargement. Understanding the mechanism of cell wall loosening may also provide new information about the molecular architecture of the plant cell wall.//
