Characterization of border species among Pythiaceae:: several Pythium isolates produce elicitins, typical proteins from Phytophthora spp.

Elicitins, holoproteins which act as inducers of hypersensitivity on tobacco, were considered as a characteristic of Phytophthora. They are also produced, along with glycosylated isoforms, by three species belonging to tie related genus Pythium, Py. vexans, Py. oedochilum and Py. marsipium, while other Pythium species do not possess such proteins. Various elicitin-like sequences were determined, bringing novel features to the elicitin family, such as an histidine residue and C-terminal extensions on the deduced peptide sequences. As the unique elicitin content of these species supports a distinct location among Pythiaceae, we suggest the separation of vexans, Py. oedochilum and Py. marsipium from Pythium and consider them as linking species between Phytophthora and Pythium.