An Extracellular Glycoprotein from Phytophthora megasperma f. sp. glycinea Elicits Phytoalexin Synthesis in Cultured Parsley Cells and Protoplasts. Jane E. Parker. Max-Planck-Institut für Züchtungsforschung, Abteilung Biochemie, D-5000 Köln 30, Germany. Wolfgang Schulte, Klaus Hahlbrock, and Dierk Scheel. Max-Planck-Institut für Züchtungsforschung, Abteilung Biochemie, D-5000 Köln 30, Germany.. MPMI 4:19-27. Accepted 13 August 1990. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1991.

A potent elicitor of phytoalexin accumulation in cultured parsley cells and protoplasts has been purified from the culture filtrate of Phytophthora megasperma f. sp. glycinea. It is a glycoprotein with an apparent relative molecular mass of 42 kDa and contains an N-linked high mannose-type sugar. Deglycosylation and proteinase treatments established that elicitor activity resides in the protein portion but was not reduced by autoclaving. In parsley cells and protoplasts the pure glycoprotein stimulated synthesis of the full complement of furanocoumarin phytoalexins normally identified in infected leaves or after treatment of cultured cells with a crude mycelial wall preparation from P. m. f. sp. glycinea. The pure glycoprotein was also shown to induce accumulation of defense-related mRNAs in parsley protoplasts in a manner similar to the crude wall elicitor. Parsley leaves did not respond to the pure glycoprotein, although the crude wall and culture filtrate preparations from P. m. f. sp. glycinea stimulated phytoalexin production when injected into leaf disks. Polyclonal antisera were raised against the intact glycoprotein and the deglycosylated protein. The former antiserum cross-reacted with many components from P. m. f. sp. glycinea, whereas the latter was monospecific. With this antiserum the 42–kDa glycoprotein was also shown to be a constituent of the cell wall but not of the soluble fraction of P. m. f. sp. glycinea. In addition, cross-reacting proteins of slightly smaller molecular mass were found in culture filtrates and mycelial cell walls of P. nicotianae var. parasitica and P. parasitica. Several other phytopathogenic fungi, however, did not contain this glycoprotein.