When plants are infested with parasites a sort of arms race is triggered. The plant tries to produce defense molecules as fast as possible to kill the intruder or at least keep it in check. At the same time the parasitic organisms are trying to overcome the plants defense responses or to turn them off altogether. An important parasitic fungus is Ustilago maydis. About 150 proteins are secreted by the fungus and are responsible for its nutrition. One of those proteins is able to redirect the plant’s metabolism in a way that it produces less salicylic acid, which is required for the production of defense molecules.