Functional analysis of the grapevine defence reaction against Armillaria mellea infection and the identification of a Phase Change Antifungal Protein

Grapevine root rot, caused by the fungus Armillaria mellea, is a serious disease of grapevine in some viticulture areas. The commonly used grapevine rootstocks are not resistant and the existing fungicides are ineffective against the disease. Field observations indicated that young plants did not show symptoms of A. mellea infection for 3-4 years, suggesting the activation of defence mechanisms. Specific defence genes such as protease inhibitors, a thaumatin and a tumour related protein appeared strongly induced in the rootstock Kober 5BB, 24 h after A. mellea inoculation, and their induction was validated in repeated experiments in vitro and under greenhouse controlled conditions. In order to elucidate the role of these genes in the plant defence response, the full-length coding sequences have been obtained and cloned in a vector suitable for heterologous expression in bacteria. Functional characterization of the purified recombinant proteins demonstrated that the protein homologous to the Quercus Phase Change Related protein inhibits A. mellea mycelia growth in vitro.