Isolation, characterization and immunolocalization of a novel, modular tomato arabinogalactan-protein corresponding to the LeAGP-1 gene

Arabinogalactan proteins (AGPs) are a family of hydroxyproline-rich glycopr oteins implicated to function in plant growth and development. This report focuses on a novel, modular AGP found in tomato, LeAGP-1,which was predicte d by DNA cloning and herein verified at the protein level as a major AGP co mponent. LeAGP-1 was isolated from tomato suspension-cultured cells and ver ified to be an AGP by precipitation with (beta-D-galactosyl)(3) Yariv pheny lglycoside and by amino acid composition analysis. Furthermore, LeAGP-1 was determined to correspond to LeAGP-1 clones based on three criteria: (1) am ino acid composition identity, (2) amino acid sequence identity, and (3) sp ecific immunoreactivity of glycosylated and deglycosylated LeAGP-1 with an antibody developed against the highly basic subdomain predicted from LeAGP- 1 clones. The antibody was also used to immunolocalize LeAGP-1 in tomato to the cell surface of suspension-cultured cells, maturing metaxylem elements in young internodes and petioles, and stylar transmitting tissue cells. At the subcellular level, LeAGP-1 immunolocalized to the cell walls of these particular cells as well as to intercellular spaces between stylar transmit ting tissue cells. LeAGP-1 now emerges as one of the most comprehensively s tudied AGPs in terms of (1) characterization at the genomic DNA, cDNA and p rotein levels, (2) known organ-specific and developmentally regulated mRNA expression patterns, (3) development of an antibody against a unique, pepti de subdomain which specifically recognizes LeAGP-1 in its glycosylated and deglycosylated states, and (4) immunolocalization of a single, well-defined AGP molecule at the tissue and subcellular levels.