The parastagonospora nodorum necrotrophic effector SnTox1 elicits recognition in wheat and then protects from the resulting host defense response

CS-9.5 - Parastagonospora nodorum (Synonym: Stagonospora nodorum) is a destructive pathogen of wheat that induces yield and quality losses by causing disease on 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 to be reported from P. nodorum and interacts directly or indirectly with the single dominant susceptibility gene Snn1. SnTox1 is recognized by Snn1 followed by the induction of a classical defense response involving programmed cell death (PCD), an oxidative burst, DNA laddering and up regulation of several PR proteins, however, this recognition results in susceptibility to P. nodorum rather than resistance. Interestingly, in addition to inducing PCD that results in susceptibility, we have shown that SnTox1 is important in defending the pathogen against wheat chitinases that attack the cell wall of fungi, reducing growth. To demonstrate that SnTox1 was involved in protection from host-produced chitinases, we cloned and expressed several wheat chitinase genes to assess the effects of chitinases in the presence and absence of the SnTox1, showing that SnTox1 is highly important in protecting the pathogen from wheat chitinases. Additionally, we transformed non-pathogens of wheat with SnTox1 and showed that not only did some of these fungi become pathogens of wheat but all had increased protection from wheat chitinases. The dual function of this protein explains the high prevalence of SnTox1 , relative to other NEs in the P. nodorum global population.