Sequences of acidic and basic elicitin isoforms secreted by Phytophthora megasperma megasperma.

Elicitins are toxic proteins secreted by Phytophthora spp. responsible for the incompatible reaction and systemic leaf necroses on tobacco. We found that Phytophthora megasperma megasperma produces two elicitin isoforms, each belonging to a different physico-chemical class, although the beta elicitin was less toxic than other beta ones. These 98 residue proteins were purified, sequenced and compared with other known elicitins. In addition to the point mutation already known to correlate with the differences in necrotic activities between alpha and beta isoforms, we found another region of the molecule likely to be involved in the regulation of the toxicity.