Poster: Cell walls

Abs # 609: Characterization of two plasma-membrane bound arabinogalactan-proteins in Arabidopsis

Presenter:	Yang, Jie , jy841001@ohio.edu
Authors	Yang, Jie  (A)   Sun, Wenxian  (B)   Kieliszewski, Marcia J. (A)   Showalter, Allan M. (A)
Affiliations:	(A): Ohio University (B): University of Wisconsin-Madison

Arabinogalactan-proteins (AGPs) are a family of highly glycosylated hydroxyproline-rich proteins that are ubiquitous on plant cell surfaces. They are proposed to play important roles in plant growth and development, including embryogenesis, programmed cell death and cell differentiation. The major AGP in tomato, LeAGP-1, has been well characterized by my lab. It has three domains: an N-terminal signal peptide, a proline / hydroxyproline-rich AGP central domain (which contains a lysine-rich subdomain) and a C-terminal glycosylphosphatidylinositol (GPI) anchor addition sequence. AtAGP17 is the Arabidopsis homolog to LeAGP-1. Northern blotting and RT-PCR revealed that it was strongly expressed leaves and stems and weakly expressed in roots and flowers. By expressing an AtAGP17-GFP (green fluorescence protein) in tobacco cells, AtAGP17 was localized to the plasma membrane and present in Hechtian strands following plasmolysis. Purified fusion protein was precipitated by â-Yariv reagent. It also produced a characteristic AGP smear using an anti-GFP antibody, with a molecular weight of 80 kD - 150 kD. Consistent with these data, carbohydrate composition and linkage analyses of purified AtAGP17-GFP confirmed that AtAGP17 is a bona fide AGP. Carbohydrate accounted for ~86% of the molecule with arabinose and galactose as major and rhamnose and glucuronic acid as minor glycosyl residues. 1, 3, 6-Gal, 1, 4-Glc A, 1, 3-Gal, and t-Ara were major linkages present in AGP17. Similar experiments are now being conducted on another LeAGP-1 homolog in Arabidopsis, namely AtAGP18.