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CELL BIOLOGY AND SIGNAL TRANSDUCTION

Molecular Interactions of Arabinogalactan Proteins with Cortical Microtubules and F-Actin in Bright Yellow-2 Tobacco Cultured Cells¹

Department of Environmental and Plant Biology (H.S.S., J.Y., A.M.S.), and Molecular and Cellular Biology Program (H.S.S., J.Y., A.M.S.), Ohio University, Athens, Ohio 45701–2979

Arabinogalactan proteins (AGPs), a superfamily of plant hydroxyproline-rich glycoproteins, are present at cell surfaces. Although precise functions of AGPs remain elusive, they are widely implicated in plant growth and development. A well-characterized classical tomato (Lycopersicon esculentum) AGP containing a glycosylphosphatidylinositol plasma membrane anchor sequence was used here to elucidate functional roles of AGPs. Transgenic tobacco (Nicotiana tabacum) Bright Yellow-2 (BY-2) cells stably expressing green fluorescent protein (GFP)-LeAGP-1 were plasmolysed and used to localize LeAGP-1 on the plasma membrane and in Hechtian strands. Cytoskeleton disruptors and -Yariv reagent (which binds and perturbs AGPs) were used to examine the role of LeAGP-1 as a candidate linker protein between the plasma membrane and cytoskeleton. This study used a two-pronged approach. First, BY-2 cells, either wild type or expressing GFP-microtubule (MT)-binding domain, were treated with -Yariv reagent, and effects on MTs and F-actin were observed. Second, BY-2 cells expressing GFP-LeAGP-1 were treated with amiprophosmethyl and cytochalasin-D to disrupt MTs and F-actin, and effects on LeAGP-1 localization were observed. -Yariv treatment resulted in terminal cell bulging, puncta formation, and depolymerization/disorganization of MTs, indicating a likely role for AGPs in cortical MT organization. -Yariv treatment also resulted in the formation of thicker actin filaments, indicating a role for AGPs in actin polymerization. Similarly, amiprophosmethyl and cytochalasin-D treatments resulted in relocalization of LeAGP-1 on Hechtian strands and indicate roles for MTs and F-actin in AGP organization at the cell surface and in Hechtian strands. Collectively, these studies indicate that glycosylphosphatidylinositol-anchored AGPs function to link the plasma membrane to the cytoskeleton.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Allan M. Showalter (showalte{at}ohio.edu).

www.plantphysiol.org/cgi/doi/10.1104/pp.106.088716

^* Corresponding author; e-mail showalte{at}ohio.edu; fax 740–593–1130.

Received August 25, 2006; accepted October 13, 2006; published October 20, 2006.

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