Discovery of Two Novel Phthalide Phytotoxins from\nthe Wheat Tan Spot Fungal Pathogen Pyrenophora tritici-repentis

The Dothideomycete\nfungal pathogen Pyrenophora tritici-repentis (Ptr) is the causal agent of the tan spot disease of wheat. The\nproteinaceous necrotrophic effectors ToxA and ToxB are well characterized.\nA nonproteinaceous effector called ToxC has also been partially characterized.\nPtr produces a number of other small molecular weight compounds, but\nthese remain poorly characterized. In this study, two novel compounds,\ndesignated ToxE1 and ToxE2, capable of inducing chlorotic symptoms\non wheat leaves in a cultivar-specific manner, were purified from\nPtr liquid cultures. There is no evidence that these compounds correspond\nto ToxC. Most isolates produced ToxE1, ToxE2, or both, and both compounds\nwere detected in infected wheat leaves. The structures of both analogues\nwere elucidated by NMR spectroscopy and comprise a phthalide core\nstructure with an amide moiety. We postulate that these compounds\nhave a general phytotoxic effect and may have an ancillary role in\ndisease development.