Investigations of how the necrotrophic specialist Parastagonospora nodorum is using the dual function necrotrophic effector SnTox1 to infect wheat

Parastagonospora nodorum (Synonym Stagonospora nodorum) is a destructive pathogen of wheat that induces yield and quality losses by causing disease on both the leaves and glumes of wheat. P. nodorum is a necrotrophic specialist pathogen that secretes an arsenal of necrotrophic effectors (NEs) involved in disease induction. SnTox1 was the first of seven NEs reported from P. nodorum and was shown to interact directly or indirectly with the single dominant susceptibility gene Snn1. The SnTox1-Snn1 interaction induces several hallmarks of a defense response including an oxidative burst and DNA laddering, a classic apoptosis response, but results in susceptibility rather than resistance. Although several necrotrophic specialists are known to induce the defense response while causing disease, little is known about how necrotrophic specialists survive the harsh environment of the host defense response. SnTox1 contains homology to several plant chitin binding proteins and we have shown that SnTox1 localizes to the cell wall of mycelium in culture and that SnTox1 binds purified chitin. We have cloned and expressed several wheat chitinases and used them to show that SnTox1 not only induces PCD but that SnTox1 also has a second role of binding chitin in the fungal cell wall, resulting in protection from these wheat chitinases. The dual function of this protein explains the high prevalence of SnTox1, relative to other NEs in the P. nodorum global population.