Structure and Function of a Novel, Modular Arabinogalactan-Protein from Tomato

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9727757; PI -- Showalter Arabinogalactan-proteins (AGPs) are a family of hydroxyproline-richglycoproteins which are widely distributed in plants. AGPs are found inintercellular spaces, cell walls, and plasma membranes and implicated toplay important roles in growth and development. This proposal focuses on aputative plasma membrane AGP, LeAGP-1, deduced from tomato DNA clones whichdemonstrate developmental and organ-specific regulation. The clonespredict a novel, modular AGP comprised of an N-terminal signal peptide, acentral classical AGP domain sandwiching a basic subdomain, and C-terminalputative transmembrane domain. Our working hypotheses are that LeAGP-1represents a plasma membrane AGP and that it functions in establishingconnections and mediating adhesion to the cell wall, analogous to animalcell adhesion molecules. The PIs will test these hypotheses and addressstructure and function of LeAGP-1 by: 1) isolating and biochemicallycharacterizing LeAGP-1 from tomato cell cultures to provide structuralinformation and material for functional characterization, 2)immunolocalizing LeAGP-1 in cultured cells, stems, and flowers and inplasmolyzed cells demonstrating zones of adhesion between the membrane andwall, and 3) functionally characterizing LeAGP-1 at the molecular level(tests for intermolecular crosslinking) and whole plant level (LeAGP-1antisense suppression/sense cosuppression in transgenic plants).