Syringolin reprograms wheat to undergo hypersensitive cell death in a compatible interaction with powdery mildew

We had previously isolated and characterized syringolin A, one of the molec ular determinants secreted by Pseudomonas syringae pv syringae that is perc eived by nonhost plant species such as rice. Here, we show that syringolin A is recognized by wheat and that it induces the accumulation of gene trans cripts and increases protection against powdery mildew when applied before inoculation. Moreover, syringolin A essentially eradicates powdery mildew f rom infected wheat if applied after inoculation. This curative effect is ac companied by the induction of cell death and the reactivation of pathogenes is-related genes whose transcript levels initially accumulate after powdery mildew inoculation but then decline during the later course of infection. Because syringolin A has no fungicidal activity against a variety of fungi and its action on wheat cannot be mimicked by the fungicide cyprodinil, syr ingolin A is hypothesized to counteract the suppression of host defense rea ctions imposed by the pathogen on the colonized cells.