SnTox3 Acts in Effector Triggered Susceptibility to Induce Disease on Wheat Carrying the Snn3 Gene

Abstract

The necrotrophic fungus Stagonospora nodorum produces multiple proteinaceous host-selective toxins (HSTs) which act in effector triggered susceptibility. Here, we report the molecular cloning and functional characterization of the SnTox3-encoding gene, designated SnTox3, as well as the initial characterization of the SnTox3 protein. SnTox3 is a 693 bp intron-free gene with little obvious homology to other known genes. The predicted immature SnTox3 protein is 25.8 kDa in size. A 20 amino acid signal sequence as well as a possible pro sequence are predicted. Six cysteine residues are predicted to form disulfide bonds and are shown to be important for SnTox3 activity. Using heterologous expression in Pichia pastoris and transformation into an avirulent S. nodorum isolate, we show that SnTox3 encodes the SnTox3 protein and that SnTox3 interacts with the wheat susceptibility gene Snn3. In addition, the avirulent S. nodorum isolate transformed with SnTox3 was virulent on host lines expressing the Snn3 gene. SnTox3-disrupted mutants were deficient in the production of SnTox3 and avirulent on the Snn3 differential wheat line BG220. An analysis of genetic diversity revealed that SnTox3 is present in 60.1% of a worldwide collection of 923 isolates and occurs as eleven nucleotide haplotypes resulting in four amino acid haplotypes. The cloning of SnTox3 provides a fundamental tool for the investigation of the S. nodorum–wheat interaction, as well as vital information for the general characterization of necrotroph–plant interactions.

Evaluation and Association Mapping of Resistance to Tan Spot and Stagonospora Nodorum Blotch in Adapted Winter Wheat Germplasm

“…be dependent on the genetic backgrounds of the pathogen and the host . The role of SnTox3 in disease has ranged from being 100% correlated (Zhang et al 2011) to weakly associated (Friesen et al 2007;Liu et al 2009) to no association due to the presence of other major NE-sensitivity gene interactions such as Sn ToxA-Tsn1 or SnTox2-Snn2 . In this case, it is most likely that the SnTox3-Snn3 interaction was masked by the ToxA-Tsn1 interaction.…”

“…The four NE genes ToxA, ToxB, SnTox1, and SnTox3 have been cloned from the two fungal pathogens and heterologously expressed in the Pichia pastoris yeast strain x33 (Abeysekara et al 2010;Liu et al 2009Liu et al , 2012. The yeast strains expressing individual NE genes were grown in yeast potato dextrose broth (Liu et al 2012) for 24 to 48 h at 30°C with agitated shaking.…”

Sensitivity to three Parastagonospora nodorum necrotrophic effectors in current Australian wheat cultivars and the presence of further fungal effectors

“…ToxA encodes a small, secreted protein that causes necrosis and promotes infection in wheat carrying the Tsn1 gene (Tan et al 2012), which is located on chromosome 5B and encodes a protein with distinct NBS-LRR (nucleotide-binding site-leucine-rich repeat) and protein kinase domains (Faris et al 2010). SnTox3 encodes a small, secreted protein (Liu et al 2009); Snn3-B1 and Snn3-D1 are key SnTox3 sensitivity genes that mapped to the short arm of chromosome 5B and 5D, respectively (Zhang et al 2011). Both effector genes are ubiquitous in Australian P. nodorum isolates.…”

“…Both effector genes are ubiquitous in Australian P. nodorum isolates. Their roles in virulence have been thoroughly demonstrated (Friesen et al 2006;Liu et al 2009;Oliver et al 2012;McDonald et al 2013).…”

Analysis of Two in Planta Expressed LysM Effector Homologs from the FungusMycosphaerella graminicolaReveals Novel Functional Properties and Varying Contributions to Virulence on Wheat

“…In the latter scenario, the net result is to promote plant infection through the activation of plant cell death signaling pathways often resembling those triggered during ETI (Wolpert et al, 2002). These mechanisms, described as effectortriggered susceptibility (Friesen et al, 2008), have been shown to favor plant infection by various necrotrophic fungi, and in particular two wheat (Triticum aestivum)-infecting fungi, Stagonospora nodorum and Pyrenophora tritici repentis (Friesen et al, 2006;Liu et al, 2009), which are the causal agents of leaf blotch and tan spot diseases, respectively.…”