Isolation of a Receptor for a Fungal-Wall-Derived Eliitor of Phytoalexins

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Isolation of a Receptor for a Fungal-Wall-Derived Elicitor of Phytoalexins: The long term goal of the research described in this proposal is the isolation and characterization of a hepta-B-glucoside receptor from soybean tissue. Fungal-derived B-glucans of the type from which the hepta-B-glucoside was isolated are active as inducers or enhancers of a variety of defense mechanisms in both plants and animals. No receptor for oligosaccharide(s) of this type has been isolated from any source. The only biologically active B-glucan fragment that has been purified to homogeneity and structurally characterized is a hepta-B-glucoside that is active at nanomolar concentrations in stimulating phytoalexin (antibiotic) accumulation in soybean tissue. The specific goals for the initial period of funding are to identify the most suitable soybean tissue from which to isolate the receptor for the active hepta-B-glucoside elicitor, to prepare various derivatives of the hepta-B-glucoside elicitor and to compare their biological activity with that of the native elicitor. These derivatives will be used to prepare (i) radiolabeled elicitor for ligand-binding studies, (ii) photo-affinity labeling reagents for receptor localization and identification studies, and (iii) affinity chromatography matrices for receptor purification. Time permitting, the elicitor derivatives will be used to initiate studies to identify putative receptors in plant extracts. Phytoalexin accumulation is believed to play an important role in plant disease resistance and also is an excellent model system for studying the regulation of gene expression in plants. Purification of the hepta-B-glucoside receptor is necessary before studies can be undertaken to identify the role the receptor(s) play in the signal pathway that results in altered gene expression leading to phytoalexin accumulation in affected plant cells. The research should increase our understanding of how plants perceive invasive microorganisms and how the recognition leads to activation of specific plant defenses.