The Wheat Snn7 Gene Confers Susceptibility on Recognition of the Parastagonospora nodorum Necrotrophic Effector SnTox7

Abstract

Parastagonospora (syn. ana, Stagonospora; teleo, Phaeosphaeria) nodorum (Berk.) Quaedvleig, Verkley & Crous is a necrotrophic fungal pathogen that causes the disease Septoria nodorum blotch (SNB) on wheat (Triticum aestivum L. subsp. aestivum). The fungus produces necrotrophic effectors (NEs) that cause cell death when recognized by corresponding host genes, which ultimately leads to disease. To date, eight host gene-NE interactions have been described in the wheat-P. nodorum system. Here, we report the identification and partial characterization of a ninth interaction involving a P. nodorum-produced NE designated SnTox7 and a wheat gene designated Snn7. SnTox7 is a small protein with an estimated size less than 30 kDa and largely resistant to heat and chemical treatment. The Snn7 gene governs sensitivity to SnTox7 and was delineated to a 2.7-cM interval on the long arm of wheat chromosome 2D. The Snn7-SnTox7 interaction explained 33% of the variation in disease among a segregating population, indicating that the interaction plays a prominent role in the development of SNB. The Snn7 sensitivity allele was identified in the hexaploid wheat cultivar Timstein, but evaluation of a set of 52 hexaploid lines of diverse origin indicated that few genotypes harbored a functional Snn7 allele, thus indicating that Snn7 is relatively rare. The identification of the Snn7-SnTox7 interaction adds to our knowledge of the wheat-P. nodorum pathosystem, which has become a model for necrotrophic specialist fungal pathogens and their interactions with plants leading to necrotrophic effector-triggered susceptibility.

Local adaptation drives the diversification of effectors in the fungal wheat pathogen Parastagonospora nodorum in the United States

“…These telomere to telomere sequences of nearly every P. nodorum chromosome, in addition to the annotation of 13,379 genes using RNA-seq, greatly improved the framework for effector discovery. A total of nine effector-host susceptibility factor interactions have been previously identified [18,33,34,35,36,37,38,39,40,41] with three of the pathogen effectors (SnToxA, SnTox1, and SnTox3) having been cloned and validated [35,36,42]. Additionally, the cognate receptor genes of SnToxA and SnTox1, Tsn1 and Snn1 , respectively, have also been cloned and characterized in wheat [34, 43].…”

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.…”

New Insights into the Roles of Host Gene-Necrotrophic Effector Interactions in Governing Susceptibility of Durum Wheat to Tan Spot and Septoria nodorum Blotch

“…To date, nine interactions involving specific wheat genes and cognate NEs have been reported in the wheat- Pa. nodorum system, and all have been shown to play significant roles in the development of SNB (Liu et al 2004a,b, 2006; Friesen et al 2006, 2007, 2008, 2009, 2012; Abeysekara et al 2009, 2012; Chu et al 2010b; Zhang et al 2011; Gao et al 2015; Shi et al 2015). One of these interactions is the Tsn1 -SnToxA (hereafter, both Ptr ToxA and SnToxA will be referred to as ToxA) interaction.…”