Elicitins, proteinaceous elicitors from Phytophthora species

Department of Biochemistry, Faculty of Science, Masaryk University, Brno, CZ Potato late blight is one of the most devastating plant diseases. The epidemics that destroyed potato crops in Europe in the 1840s led to mass starvation. For example, in the Great Irish Famine of 1845 to 1847 up to one million people died and a similar number of people emigrated to the rest of Europe and the USA. There were, of course, factors that contributed to the starvation, including the land-tenure system in Ireland at that time, and the almost total dependence of the poorer working population on potatoes as their source of food. Nevertheless, potato blight ranks as one of the most devastating diseases in human history. Even today it is one of the major pathogens that chemical companies target in their search for new fungicides. The disease is caused by a fungus-like organism, Phytophthora infestans, which is a specialized pathogen of potato and, to a lesser extent, tomato (another member of the plant family Solanaceae). Elicitins are small hydrophilic proteins (Mr 10 kDa), secreted by Phytophthora species, with three disulfide bridges and hydrophobic core able to bind lipids. Most of these proteins cause hypersensitive-like reaction in tobacco plants. We have shown that these elicitors are carrier proteins able to transfer sterols between biological membranes. Using mutated proteins with modified affinity to sterols we suggest that the active form triggering the defense reaction could be the complex elicitin-sterol. Our present project consists in modeling of the interactions of Phytophthora elicitors (cryptogein) with lipids in order to find a mutant with specific properties. We prepared a series of cryptogein mutants, an elicitor from Phytophthora cryptogea, with the altered abilities to bind sterols and fatty acids. The induction of the early events, i.e. synthesis of active oxygen species and pH changes, in suspension tobacco cells by these mutated proteins was proportional to their ability to bind sterols but not fatty acids. Although the cryptogein-sterol complex was suggested to be a form triggering a defense reaction in tobacco some proteins unable to bind sterols induced the synthesis of active oxygen species and pH changes. The modeling experiments showed that conformational changes after the introduction of bulky residues into the omega loop of cryptogein resemble those induced by sterol binding. These changes may be necessary for the ability to trigger the early events by elicitins. However, the ability to stimulate necrosis in suspension tobacco cells and the expression of defense proteins in tobacco plants were neither linked to the lipid binding capacity nor to the capacity to provoke the early events. On the basis of these experiments and previous results, we propose that elicitins could stimulate two signal pathways. The first one induces necroses and the expression of pathogen-related proteins, includes tyrosine protein kinases and mitogen-activated protein kinases and depends on the overall structure and charge distribution. The second type of the interaction is mediated by phospholipase C and protein kinase C. It triggers the synthesis of active oxygen species and pH changes. This interaction depends on the ability of elicitins to bind sterols. Cooperation projects with: Phytopharmacy Laboratory, UA 692 INRA/Université de Bourgogne, Dijon, France (Dr. J.-P. Blein). National Center of Biomolecul Research, Masaryk University Brno (Prof.. J. Damborsky) UMR IPMSV, Sophia Antipolis, 400 Route des Chappes, France (Dr. M. Ponchet) Institute of Experimental Botany, Academy of Science of Czech Republic, Prague (dr. M. Sindelarova) "Source":[ http://www.sci.muni.cz/~mikes/fungi.html#Laboratory%20of%20plant-pathogen%20interactions]

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