Gastrodianin-like mannose-binding proteins: a novel class of plant proteins with antifungal properties

The orchid Gastrodia elata depends on the fungus Armillaria mellea to compl ete its life cycle. In the interaction, fungal hyphae penetrate older, nutr itive corms but not newly formed corms. From these corms, a protein fractio n with in vitro activity against plant-pathogenic fungi has previously been purified. Here, the sequence of gastrodianin, the main constituent of the antifungal fraction, is reported. Four isoforms that encoded two different mature proteins were identified at the cDNA level. Another isoform was dete cted in sequenced peptides. Because the antifungal activity of gastrodianin s produced in and purified from Escherichia coil and Nicotiana tabacum was comparable to that of gastrodianin purified from the orchid, gastrodianins are the active component of the antifungal fractions. Gastrodianin accumula tion is probably an important part of the mechanism by which the orchid con trols Armillaria penetration. Gastrodianin was found to be homologous to mo nomeric mannose-binding proteins of other orchids, of which at least one (E pipactis helleborine mannose-binding protein) also displayed in vitro antif ungal activity. This establishes the gastrodianin-like proteins (GLIPs) as a novel class of antifungal proteins.