Oligandrin. A Proteinaceous Molecule Produced by the MycoparasitePythium oligandrum Induces Resistance to Phytophthora parasitica Infection in Tomato Plants

Abstract

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.

Diverse responses of wild and cultivated tomato to BABA, oligandrin andOidium neolycopersiciinfection

“…The proteinaceous elicitor oligandrin from P. oligandrum, representing elicitins as the best known oomycete pathogen-associated molecular pattern (M/PAMPs), induces the HR and SAR in several plants (Picard et al, 2000;Benhamou et al, 2001). BABA represents a nonprotein amino acid generally accepted as a potent priming agent conferring increased resistance to biotic and abiotic stresses in many studied plants.…”

“…Apart from its mycoparasitical activity, oligandrin adversely affects pathogen growth and development in the host plant and confers enhanced resistance in many plants against various pathogens, i.e. tomato to Phytophthora parasitica (Picard et al, 2000) and Fusarium oxysporum f. sp. radicis-lycopersici (Benhamou et al, 2001) or tobacco to P. parasitica and to phytoplasma (Lherminier et al, 2003).…”

La résistance induite : une nouvelle stratégie de défense des plantes contre les agents pathogènes

“…1994). Les mécanismes sousjacents à l'élaboration de ces barrières de renforcement de la paroi végétale incluent le dépôt de callose suite à l'activation de la të-1,3-glucane-synthase par le Ca 2+ (Benhamou et al 1994), l'incrustation de lignine et subérine (Benhamou et al 2000), l'infiltration de composés phénoliques pré-existants (Benhamou et al 2000) et l'accumulation de glycoprotéines riches en hydroxyproline (HRGPs pour hydroxyproline-rich glycoproteins) (Benhamou et al 1990). Tous ces mécanismes ont en commun de contribuer à consolider l'architecture pariétale, ralentissant ainsi la pénétration de l'agent pathogène ainsi que la diffusion des toxines et des enzymes microbiennes dans les tissus, et laissant à la plante le temps d'activer les autres voies de synthèse menant à la production de molécules de défense à action directe (Benhamou 1996).…”

“…(Ricci et al 1989), s'est révélée être un puissant inducteur de réactions de défense chez la tomate infectée par le Phytophthora parasitica Dast. (Picard et al 2000). Les mécanis-mes par lesquels agit cet éliciteur ne sont pas encore clairement définis.…”

“…Les mécanis-mes par lesquels agit cet éliciteur ne sont pas encore clairement définis. Cependant, l'analyse du profil de migration de l'oligandrine après iodination a montré que la molécule se propageait rapidement dans tous les organes de la plante, probablement via le système vasculaire (Picard et al 2000). Ces résultats indiquent donc que l'oligandrine, à la manière des autres élici-tines connues , est elle-même un signal de stress systémi-que indiquant aux cellules de la plante l'état d'urgence.…”