Genetic Dissection of Wheat-Necrotrophic Pathogen Interactions

Stagonosporanodorum is a necrotrophic pathogen of wheat, and over the past decade, we have dissected the genetic components of the wheat-S. nodorumpathosystem. S. nodorum produces numerous host-selective toxins (HSTs) that interact with specific dominant host genes in an inverse gene-for-gene manner to cause disease.  In recent years, we have cloned the wheat genes Tsn1 and Snn1, which recognize the HSTs SnToxA and SnTox1, respectively, leading to susceptibility. Tsn1 is a member of the NB-LRR class of disease ‘resistance’ genes, which typically activate effector-triggered immunity (ETI) in response to biotrophic pathogens, and Snn1 is a wall-associated kinase (WAK), which is a class of receptor kinases known to activate PAMP-triggered immunity (PTI) pathways in response to biotrophic pathogens. Indeed, recognition of SnToxA and SnTox1 by Tsn1 and Snn1 activates a defense response and programmed cell death, but because the pathogen is a necrotroph, it is able to gain nutrients and sporulate, which leads to disease. These results demonstrate that necrotrophic pathogens such as S. nodorum can hijack host molecular pathways driven by different classes of genesthat typically confer resistance to biotrophic pathogensthus revealing the remarkably sophisticated nature of plant-necrotrophic pathogen interactions.