Fig. 4. Overview of the Snn1-SnTox1 and Tsn1-SnToxA interactions and known downstream events that result in NETS in the wheat–P. nodorum pathosystem.

The SnTox1 and SnToxA proteins are secreted by the fungus. SnToxA is internalized into the cell (23), but SnTox1 is not (11). Upon recognition of SnTox1 and SnToxA by the Snn1 and Tsn1 proteins, respectively, signaling leading to up-regulation of defense response pathways and events resulting in programmed cell death (9, 11) ultimately provide a means for the pathogen to gain nutrients and reproduce. Plants with either Tsn1 or Snn1 are susceptible, and plants with both genes experience even higher levels of disease (24). Elimination of both genes renders the plant resistant.