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Identification and Characterization of the SnTox6-Snn6 Interaction in the Parastagonospora nodorum–Wheat Pathosystem

Y. Gao, J. D. Faris, Z. Liu, Y. M. Kim, R. A. Syme, R. P. Oliver, S. S. Xu, T. L. Friesen
Molecular plant-microbe interactions 2015 v.28 no.5 pp. 615-625
quantitative trait loci, chromosomes, Parastagonospora nodorum, fungal diseases of plants, host-pathogen relationships, necrosis, gene interaction, models, reverse transcriptase polymerase chain reaction, wheat, gene expression, chromosome mapping, Triticum aestivum, fungal proteins, genes, pathogens, fungi
Stagonospora nodorum (teleomorph; Phaeosphaeria nodorum), is a necrotrophic filamentous fungal pathogen that causes Stagonospora nodorum blotch (SNB) on wheat. S. nodorum produces necrotrophic effectors (NE) that are recognized by dominant host sensitivity gene products resulting in disease development. The NE-host sensitivity gene interaction is critical to inducing effector-triggered susceptibility. Currently, seven NE-host sensitivity gene interactions have been identified in the S. nodorum-wheat pathosystem and each of them follows an inverse gene-for-gene model resulting in effector triggered susceptibility. Here we use the ITMI wheat mapping population, which we have previously shown to segregate for sensitivity to SnTox1 (Snn1) and SnTox3 (Snn3-B1) to show for the first time the identification of the novel NE SnTox6, the identification and mapping of Snn6 the corresponding wheat sensitivity gene, and the characterization of the significance of the SnTox6-Snn6 interaction. SnTox6 is a novel proteinaceous NE with an estimated size of 5-12 kDa that induces necrosis on wheat lines harboring Snn6. Snn6 confers sensitivity to SnTox6 and resides at the distal end of the long arm of wheat chromosome 6A. The SnTox6-Snn6 interaction was light dependent, and accounted for 27% of the variation in SNB disease development in the ITMI population. Interestingly, no other significant QTL were identified even though the S. nodorum isolate used in this study (Sn6) harbors both the SnTox1 and SnTox3 genes. RT-PCR showed that SnTox3 was expressed at high levels 72 h post inoculation; however, SnTox1 was not expressed at the same time point, the time point previously shown to be the peak of SnTox1 and SnTox3 in planta expression, showing that gene regulation of necrotrophic effectors is isolate specific. This work expands our knowledge of the wheat-S. nodorum interaction and further establishes this system as a model for other host-necrotroph pathosystems.