Signal perception and intracellular signal transduction in plant pathogen defense

Disease resistance in plant/pathogen interactions requires sensitive and specific recognition mechanisms for pathogen-derived signals in plants. Cultured parsley (Petroselinum crispum) cells respond to treatment with a crude cell wall preparation derived from the phytopathogenic fungus Phytophthora sojae with transcriptional activation of the same set of defense-related genes as are activated in parsley leaves upon infection with fungal spores. A 13 amino acid core sequence (Pep-13) of a 42 kDa fungal cell wall glycoprotein was identified which stimulates the same responses as the crude cell wall elicitor, namely macroscopic Ca2+ and H+-influxes, effluxes of K+- and Cl- ions, production of active oxygen species (oxidative burst), defense-related gene activation, and formation of antifungal phytoalexins. Using [I-125]Tyr-Pep-13 as ligand in binding assays, a single-class high-affinity binding site in parsley microsomal membranes and protoplasts could be detected. Binding was specific, saturable, and reversible. By chemical crosslinking, a 91 kDa parsley plasma membrane protein was identified to be the receptor of the peptide elicitor. Isolation of this receptor protein involved in pathogen defense in plants is under way.