Identification and Characterization of the SnTox6-Snn6Interaction in theParastagonospora nodorum–Wheat Pathosystem

Abstract

Parastagonospora nodorum is a necrotrophic fungal pathogen that causes Septoria nodorum blotch (SNB) (formerly Stagonospora nodorum blotch) on wheat. P. nodorum produces necrotrophic effectors (NE) that are recognized by dominant host sensitivity gene products resulting in disease development. The NE-host interaction is critical to inducing NE-triggered susceptibility (NETS). To date, seven NE-host sensitivity gene interactions, following an inverse gene-for-gene model, have been identified in the P. nodorum-wheat pathosystem. Here, we used a wheat mapping population that segregated for sensitivity to two previously characterized interactions (SnTox1-Snn1 and SnTox3-Snn3-B1) to identify and characterize a new interaction involving the NE designated SnTox6 and the host sensitivity gene designated Snn6. SnTox6 is a small secreted protein that induces necrosis on wheat lines harboring Snn6. Sensitivity to SnTox6, conferred by Snn6, was light-dependent and was shown to underlie a major disease susceptibility quantitative trait locus (QTL). No other QTL were identified, even though the P. nodorum isolate used in this study harbored both the SnTox1 and SnTox3 genes. Reverse transcription-polymerase chain reaction showed that the expression of SnTox1 was not detectable, whereas SnTox3 was expressed and, yet, did not play a significant role in disease development. This work expands our knowledge of the wheat-P. nodorum interaction and further establishes this system as a model for necrotrophic specialist pathosystems.

Disease Impact on Wheat Yield Potential and Prospects of Genetic Control

“…The HSTs interact with the host genes in an inverse gene-for-gene manner (toxin model) wherein products of sensitivity genes in the host recognize the effectors produced by the fungus and trigger a hypersensitive response, leading to increased susceptibility in the field. Although seven HSTs have been identified (32), indicating pathogen diversity, race specialization remains inconclusive.…”

Regulation of proteinaceous effector expression in phytopathogenic fungi

“…The P . nodorum -wheat pathosystem is also governed by other effector—host dominant sensitivity gene interactions [38,39,40]. Thus far, genes encoding for the effectors and their matching host genes have yet been identified.…”

“…The P . nodorum —wheat pathosystem is unique in that effector—effector epistatic interaction has been described in several studies [39,86,87,88]. However, the mechanisms accounting for epistasis between effector—host dominant susceptibility gene interactions are largely unknown.…”

Marker development, saturation mapping, and high-resolution mapping of the Septoria nodorum blotch susceptibility gene Snn3-B1 in wheat

“…To date, nine NE-host sensitivity gene interactions have been identified in the wheat-P. nodorum pathosystem including Tsn1-SnToxA Liu et al 2006;Faris et al 2010), Snn1-SnTox1 (Liu et al 2004a(Liu et al , b, 2012Reddy et al 2008), Snn2-SnTox2 (Friesen et al 2007;Zhang et al 2009), Snn3-B1-SnTox3 Liu et al 2009), Snn3-D1-SnTox3 , Snn4-SnTox4 (Abeysekara et al 2009), Snn5-SnTox5 , Snn6-SnTox6 (Gao et al 2014), and Snn7-SnTox7 (Shi et al 2015). The pathogen genes encoding three of the NEs, including SnToxA , SnTox1 (Liu et al 2012), and SnTox3 (Liu et al 2009), have been cloned.…”