Arabinogalactan-proteins (AGPs) are a family of hydroxyproline-rich glycoproteins which are widely distributed in plants. AGPs are found in intercellular spaces, cell walls, and plasma membranes and implicated to play important roles in growth and development. This proposal focuses on a putative plasma membrane AGP, LeAGP-1, deduced from tomato DNA clones which demonstrate developmental and organ-specific regulation. The clones predict a novel, modular AGP comprised of an N-terminal signal peptide, a central classical AGP domain sandwiching a basic subdomain, and C-terminal putative transmembrane domain. Our working hypotheses are that LeAGP-1 represents a plasma membrane AGP and that it functions in establishing connections and mediating adhesion to the cell wall, analogous to animal cell adhesion molecules. The PIs will test these hypotheses and address structure and function of LeAGP-1 by: 1) isolating and biochemically characterizing LeAGP-1 from tomato cell cultures to provide structural information and material for functional characterization, 2) immunolocalizing LeAGP-1 in cultured cells, stems, and flowers and in plasmolyzed cells demonstrating zones of adhesion between the membrane and wall, and 3) functionally characterizing LeAGP-1 at the molecular level (tests for intermolecular crosslinking) and whole plant level (LeAGP-1 antisense suppression/sense cosuppression in transgenic plants).
