Characterization of the binding of alpha-L-Fuc (1 -> 2)-beta-D-Gal (1 ->),a xyloglucan signal, in blackberry protoplasts

Previous work showed that the fucose-->galactose moiety of the xyloglucan n onasaccharide XXFG is responsable for its biological activity. We used this side chain of XXFG (alpha-L-Fuc (1-->2)-beta-D-Gal (1-->)) in ligand-bindi ng experiments to demonstrate its role as a signal molecule in plant cells. Proteins solubilized from plasma membrane enriched fractions isolated from Rubus fruticosus protoplasts were tested for their ability to bind the sid e chain of XXFG, using a digoxigenin- or biotin-conjugated neoglycoprotein specific for 2'-fucosyl-lactose in blots and k-ELISA tests. A putative rece ptor for the signaling sugar was identified, and the ligand specificity is reported. The role of structural elements important for biological activiti es was investigated using compounds structurally related to xyloglucan, and a variety of phytohormones such as 2,4-D. (C) 2000 Published by Elsevier S cience Ireland Ltd. All rights reserved.