STRUCTURES OF ELICITIN ISOFORMS SECRETED BY PHYTOPHTHORA-DRECHSLERI

Most of the phytopathogenic fungi Phytophthora secrete holoproteins (elicitins) responsible for the incompatible reaction and systemic leaf necroses on tobacco. We found that Phytophthora drechsleri produces several elicitin isoforms of various toxicity on tobacco. The CD spectra showed that their secondary structure was largely conserved, exhibiting ca 50% alpha-helix and little or no beta-structure. These 98 residue proteins were sequenced and compared with other known elicitins. Only one point mutation correlated with the differences in necrotic activities. This residue could be either an active or a regulatory site, involved in the interaction with a receptor responsible for necrosis induction.