Submitted to: PLoS Pathogens
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/17/2011
Publication Date: 1/5/2012
Citation: Liu, Z., Zhang, Z., Faris, J.D., Oliver, R.P., Syme, R., Mcdonald, M.C., Mcdonald, B.A., Solomon, P.S., Lu, S., Shelver, W.L., Xu, S.S., Friesen, T.L. 2012. The cysteine rich necrotrophic effector SnTox1 produced by Stagonospora nodorum triggers susceptibility of wheat lines harboring Snn1. PLoS Pathogens. 8(1):e1002467. Interpretive Summary: In this manuscript we describe the cloning of SnTox1, the gene responsible for disease induced on wheat lines carrying the Snn1 gene, the corresponding susceptibility gene to SnTox1. We verified the function of the SnTox1 gene by expressing it in a yeast culture where the resulting culture filtrate caused necrosis but only on wheat lines that carried the corresponding susceptibility gene Snn1. The SnTox1 gene was also transformed into an avirulent S. nodorum isolate, creating a virulent isolate on wheat lines carrying Snn1. SnTox1 was also disrupted in virulent isolates which eliminated the ability of these strains to cause disease on wheat lines carrying Snn1 alone. Additionally we investigated the host response to SnTox1 and S. nodorum strains carrying SnTox1 and discovered that several hallmarks of a resistance response are present during the susceptible reaction showing that the necrotrophic pathogen S. nodorum may be using a resistance like response of the host to induce disease and subsequently spread in the plant tissue.
Technical Abstract: The gene encoding SnTox1, a necrotrophic effector from Stagonospora nodorum that causes necrosis of wheat lines expressing Snn1, has been verified by heterologous expression in Pichia pastoris. SnTox1 encodes a 117 amino acid cysteine rich protein with the first 17 amino acids predicted as a signal peptide. The transformation of SnTox1 into an avirulent S. nodorum isolate was sufficient to make the strain pathogenic. Additionally, the deletion of SnTox1 in virulent isolates rendered the SnTox1 mutated strains avirulent on an Snn1 differential wheat line. SnTox1 was present in 85% of a global collection of S. nodorum isolates. We identified 11 protein haplotypes and found evidence for strong diversifying selection operating on SnTox1. The SnTox1-Snn1 interaction results in an oxidative burst, DNA laddering, and pathogenesis-related gene expression, all hallmarks of a defense response. In the absence of light, SnTox1-induced necrosis and disease symptoms were completely blocked. By comparing the infection processes of a GFP-tagged avirulent isolate and the same isolate transformed with SnTox1, we conclude that SnTox1 may play a critical role in penetration. This research provides important insights into the molecular basis of the wheat-S. nodorum interaction, an emerging model for necrotrophic pathosystems.