Plant Physiol, September 2000, Vol. 124, pp. 379-396

Oligandrin. A Proteinaceous Molecule Produced by the Mycoparasite Pythium oligandrum Induces Resistance to Phytophthora parasitica Infection in Tomato Plants¹

Laboratoire de Microbiologie et Sécurité Alimentaire, Université de Brest, Technopôle Brest-Iroise, 29200 Plouzané, France (K.P., P.R., Y.T.); Unité de Recherche Santé Végétale et Environnement, Phytopathologie, Institut National de la Recherche Agronomique, BP 2078, 06606 Antibes, France (M.P.); Institut National de la Recherche Agronomique, Unité Mixte de Recherche 692, Laboratoire de Phytopharmacie et Biochimie des Interactions Cellulaires, BV 1540, 21034 Dijon cedex, France (J.-P.B.); and Recherche en Sciences de la Vie et de la Santé, Pavillon Charles-Eugène Marchand, Laval University, Sainte-Foy, Québec, Canada G1K 7P4 (N.B.)

A low-molecular weight protein, termed oligandrin, was purified to homogeneity from the culture filtrate of the mycoparasitic fungus Pythium oligandrum. When applied to decapitated tomato (Lycopersicon esculentum Mill. var. Prisca) plants, this protein displayed the ability to induce plant defense reactions that contributed to restrict stem cell invasion by the pathogenic fungus Phytophthora parasitica. According to its N-terminal sequence, low-molecular weight, acidic isoelectric point, ultraviolet spectrum, and migration profile, the P. oligandrum-produced oligandrin was found to share some similarities with several elicitins from other Phytophthora spp. and Pythium spp. However, oligandrin did not induce hypersensitive reactions. A significant decrease in disease incidence was monitored in oligandrin-treated plants as compared with water-treated plants. Ultrastructural investigations of the infected tomato stem tissues from non-treated plants showed a rapid colonization of all tissues associated with a marked host cell disorganization. In stems from oligandrin-treated plants, restriction of fungal growth to the outermost tissues and decrease in pathogen viability were the main features of the host-pathogen interaction. Invading fungal cells were markedly damaged at a time when the cellulose component of their cell walls was quite well preserved. Host reactions included the plugging of intercellular spaces as well as the occasional formation of wall appositions at sites of potential pathogen entry. In addition, pathogen ingress in the epidermis was associated with the deposition of an electron-opaque material in most invaded intercellular spaces. This material, lining the primary walls, usually extended toward the inside to form deposits that frequently interacted with the wall of invading hyphae. In the absence of fungal challenge, host reactions were not detected.