The objective of this research is to isolate and characterize the receptor for a biologically active hepta-B-glucoside. A radiolabeled hepta-B-glucoside elicitor, for use in ligand- binding studies, will be prepared by conjugation of the oligosaccharide to tyramine, followed by iodination of the conjugate. It has been established that a model heptaglucoside, maltoheptaose, can be conjugated to tyramine and furthermore, that the structural modifications of the hepta-B-glucoside elicitor required for radiolabeling with iodine are unlikely to affect its elicitor activity. A photoaffinity labeling reagent for receptor localization and identification studies will also be prepared. The receptor(s) for the hepta-B-glucoside elicitor will be identified and localized using standard cell fractionation techniques, ligand-binding assays, and photo-affinity labeling. If an elicitor receptor is identified, it will be purified and characterized. The proposed experiments will lay the groundwork for future studies to determine the physiological significance of the receptor(s) and to identify the role the receptor(s) play in the signal pathway that results in altered gene expression leading, in turn, to phytoalexin accumulation in affected plant cells.%%% Fungal-derived B-glucans, of the type from which the active hepta-B-glucoside was isolated, are active as inducers or enhancers of a variety of defense mechanisms in plants. The only biologically active B-glucan-derived fragment that has been purified to homogeneity and structurally characterized is a hepta-B-glucoside elicitor. Induction of phytoalexin accumulation by the hepta-B-glucoside elicitor is an excellent model system for the study of the structure and function of oligosaccharide receptors in plants because the complete structure of the oligosaccharide ligand has been determined and considerable information is known about the genes whose transcription is induced in plant cells upon binding of the oligosaccharide. The proposed studies, if successful, will be particularly important in plants, since plant receptors for regulatory molecules have not yet been purified and characterized.***//
