Perception and transduction of an elicitor signal in cultured parsley cells.

Treatment of cultured parsley cells or protoplasts with a purified extracellular glycoprotein from Phytophthora megasperma f.sp. glycinea induces the transcription of the same set of defence-related genes as is activated in parsley leaves upon infection. Elicitor activity was shown to reside in a specific portion of the protein moiety which was isolated, sequenced and synthesized. Partial cDNAs encoding the entire mature protein as well as other related proteins have been isolated, indicating the presence of a small gene family. The elicitor-active oligopeptide is located in the C-terminal portion of the deduced amino acid sequence. Binding of the elicitor to target sites on the parsley plasma membrane appears to be the initial event in defence gene activation. The subsequent intracellular transduction of the elicitor signal was shown to involve rapid and transient influxes of Ca2+ and H+, as well as effluxes of K+ and Cl-. Inhibition of elicitor-induced ion fluxes by channel blockers also inhibited phytoalexin synthesis, while stimulation of similar ion fluxes by treatment of cells or protoplasts with the polyene antibiotic, amphotericin B, induced the production of phytoalexins and activated the complete set of defence-related genes in the absence of elicitor.