Syringicin, a new ?-elicitin from an isolate of Phytophthora syringae, pathogenic to citrus fruit

Syringicin (Syr), a new acidic ?-elicitin, has been isolated from culture filtrates of Phytophthora syringae, which is the causal agent of citrus fruit rot. Its molecular weight (10194.6±0.2) determined by ES-MS is very similar to that calculated using the mean isotopic composition and considering the occurrence of disulfide bridges. The primary structure was obtained by the combined use of Edmann degradation with MALDI-MS and by comparison with already known a-elicitins. Syr induces a hypersensitive response and electrolyte leakage in tobacco. These are characteristic elicitor properties of the group and in agreement with the molecular mechanism recently proposed for this kind of protein. Finally, its possible applications in biological agriculture and biomedicine are briefly discussed.