Relationship between secondary structure of elicitins,proteinaceous elicitors of Phytophthora sp. and defensereaction induced in tobacco cells.

Elicitins are secreted specifically by the fungi Oomycete genera Pythium and Phytophthora [1, 2]. Biological function of elicitins is currently unknown. The response is induced by the interaction of elicitins with a putative receptor located on the cytoplasmic membrane. The transfer of signal through the receptor triggers phosphorylation-dephosphorylation cascades in the tobacco resulting in alkalization of the extracellular medium, efflux of potassium and chloride ions, influx of calcium, production of the active species from oxygen [3, 4], changes in composition of the cell wall and the induction of acquired systemic resistance. Binding of sterols to the cavity of cryptogein (elicitin from P. cryptogea) seems to be essential for consecutive association of the cryptogein with a receptor and induction of a biological response in a plant [5]. We prepared a series of mutants of cryptogein, one of the most potent elicitors of this group, with altered capacity of binding sterols (L19-R, I63-F, L15-W, L36-F, M35-F, M35-W, M59-W, M59-F). We compared the physicochemical parameters of sterol-cryptogein binding, their ability to induce the synthesis of active oxygen species, ion fluxes, their necrotic activity on tobacco suspension cells and the ability to induce the expression of pathogen related (PR) proteins in plants. The results showed that some of the early events are proportional to the affinity of cryptogein to bind sterols whereas the others (necrotic effect and the induction of PR protein synthesis) seemed to be dependent on the overall cryptogein structure.