Modifications of plant cell activities by polypeptides secreted by Eutypa lata, a vineyard fungal pathogen

Eutypa dieback is a devastating disease induced in vineyards by the fungal pathogen Eutypa lata. The fungus colonizes the xylem tissues of trunk and cordons but is never found in the annual canes. Nevertheless, dwarfed shoots and leaf necrosis observed in diseased plants indicate that a necrotic signal can spread at a distance from the infected area. Eutypine, a small cyclic molecule, and related compounds have been postulated as the toxins inducing these symptoms. In this work, we evidence that E. lata secreted other metabolites of polypeptidic nature which induced toxic effects on canes and leaves of vines, and on leaves of other plant materials. The polypeptide fraction (PF) isolated from culture medium of mycelium induced transitory H+ fluxes and membrane depolarization of plant cells. Complementary assays with plasma membrane vesicles (PMV) showed that H+-ATPase is a primary site of action as indicated by inhibition of the enzyme activity and increase of H+ conductance of plasma membrane. The toxic effect was also obvious on respiration and photosynthesis. All these impairments led to a hindering in cell energetics and, as a consequence, to an inhibition of uptake of assimilates. Treatment with PF also triggered biological events, characteristics of elicitation as suggested by the early responses on cell membrane described above, the activation of NADPH oxidase and the activation of Phenylalanine ammonia lyase (PAL).