A Gene Encoding a Host-Specific Elicitor Protein of Phytophthora parasitica. Sophien Kamoun. Center for Engineering Plants for Resistance Against Pathogens, University of California, Riverside 92521-0122 U.S.A. Kevin M. Klucher(1), Michael D. Coffey(2), and Brett M. Tyler(1,3). (1)Center for Engineering Plants for Resistance Against Pathogens and (3)Department of Plant Pathology, University of California, Davis 95616, and (2)Department of Plant Pathology, University of California, Riverside 92521-0122 U.S.A. MPMI 6:573-581. Accepted 22 June 1993. Copyright 1993 The American Phytopathological Society.

Extracellular elicitor proteins (elicitins) from Phytophthora species induce local and distal defense responses specifically in plants of the Solanaceae and Cruciferae. Based on elicitin amino acid sequences, elicitin-coding sequences from P. parasitica were amplified by the polymerase chain reaction. A genomic clone containing a complete elicitin gene, parA1, was isolated and sequenced. Elicitin was confirmed to be encoded as a precursor protein containing a 20–amino acid signal peptide that is processed before secretion. Bacterial expression of the cloned elicitin gene as a translational fusion protein containing glutathione S-transferase yielded a biologically active protein capable of inducing a hypersensitive response in tobacco, suggesting that fungus-specific postranslational modifications of elicitin are not required for its activity. Southern blot analysis indicated that elicitin genes occur as a multigene family (at least two to 10 copies) in P. parasitica, P. capsici, P. citricola, P. citrophthora, P. cryptogea, P. drechsleri, P. megasperma, and P. palmivora. Some isolates of P. parasitica that did not produce elicitins still contained elicitin-coding sequences but did not accumulate elicitin mRNA.