Filamentous fungi are prolific secretors of a diverse range of molecules, including effector proteins and phytotoxins with bioactivities against various types of crops. Pyrenophora tritici-repentis (Ptr) is the causal agent of the tan spot disease that affects global wheat production. Ptr, known as a necrotroph secretes multiple effectors to facilitate host colonisation. ToxA and ToxB are both well-characterised proteinaceous effectors while the structure of ToxC, a low-molecular weight effector molecule remains to be elucidated. Despite the advances in our understanding of protein effector biology, we still have much to explore as the mechanisms of infection are extensive and involve not only secreted proteins but also small metabolites.
Here, we present the discovery of two bioactive novel secondary (or specialised) metabolites from Ptr. Although neither compound has properties consistent with ToxC, both compounds induce chlorosis in a cultivar-specific manner but with different intensity levels. Response of chlorosis was light-dependent and one compound exhibited phytotoxicity on non-host plants. We postulate that these compounds may have an ancillary role in disease development.