Identification and characterization of a novel host–toxin interaction in the wheat–Stagonospora nodorum pathosystem

Abstract

Stagonospora nodorum, casual agent of Stagonospora nodorum blotch (SNB) of wheat, produces a number of host-selective toxins (HSTs) known to be important in disease. To date, four HSTs and corresponding host sensitivity genes have been reported, and all four host-toxin interactions are significant factors in the development of disease. Here, we describe the identification and partial characterization of a fifth S. nodorum produced HST designated SnTox4. The toxin, estimated to be 10-30 kDa in size, was found to be proteinaceous in nature. Sensitivity to SnTox4 is governed by a single dominant gene, designated Snn4, which mapped to the short arm of wheat chromosome 1A in a recombinant inbred (RI) population. The compatible Snn4-SnTox4 interaction is light dependent and results in a mottled necrotic reaction, which is different from the severe necrosis that results from other host-toxin interactions in the wheat-S. nodorum pathosystem. QTL analysis in a population of 200 RI lines derived from the Swiss winter wheat varieties Arina and Forno revealed a major QTL for SNB susceptibility that coincided with the Snn4 locus. This QTL, designated QSnb.fcu-1A, explained 41.0% of the variation in disease on leaves of seedlings indicating that a compatible Snn4-SnTox4 interaction plays a major role in the development of SNB in this population. Additional minor QTL detected on the short arms of chromosomes 2A and 3A accounted for 5.4 and 6.0% of the variation, respectively. The effects of the three QTL were largely additive, and together they explained 50% of the total phenotypic variation. These results provide further evidence that host-toxin interactions in the wheat-S. nodorum pathosystem follow an inverse gene-for-gene model.

New Quantitative Trait Loci in Wheat for Flag Leaf Resistance to Stagonospora nodorum Blotch

“…Therefore, it is reasonable to assume that QSnl04.daw-1B and QSnl05.daw-1B are different from those previously reported on 1BS (13,16,17) based on comparative chromosomal map position for markers associated with QTL. If toxin insensitivity is associated with QTL on 1BS in this study, then a gene or genes (1,21) but the lack of common markers between genetic maps did not allow unambiguous co-location for seedling and flag leaf resistance at this locus. It was expected that QSnl04.daw-2A and QSnl05.daw-2A would reside in the same marker interval; however, analysis using data from successive years showed overlapping QTL.…”

“…A number of QTL for seedling resistance have been identified using biparental mapping populations as residing on wheat chromosomes 1B, 2B, 2D, 4B, 5A, 5B, 5D, and 6A (1,4,8,14,17,22). QTL for seedling resistance on chromosomes 6A and 7A were recently identified in association mapping studies (2).…”

Proteinaceous necrotrophic effectors in fungal virulence

“…These are SnTox1, SnTox2 and SnTox4. However, genes that code for these proteins have yet to be identified and therefore, the extent of their involvement in fungal virulence cannot be fully gauged (Liu et al 2004;Friesen et al 2007;Reddy et al 2008;Abeysekara et al 2009). The wheat genes that confer sensitivity to these effectors are Snn1, Snn2 and Snn4, respectively.…”

“…The wheat genes that confer sensitivity to these effectors are Snn1, Snn2 and Snn4, respectively. The use of molecular marker-based quantitative trait locus (QTL) analysis of various mapping populations of wheat has led to the identification of major QTLs in wheat chromosome arms 1BS (Snn1), 2DS (Snn2) and 1AS (Snn4) that accounted for up to 58%, 47% and 41% in disease variations, respectively (Friesen et al 2008a;Abeysekara et al 2009). …”

Molecular characterization and genomic mapping of the pathogenesis-related protein 1 (PR-1) gene family in hexaploid wheat (Triticum aestivum L.)

“…Primers revealing polymorphisms were subsequently used to genotype the corresponding RI mapping population and each RI line was scored as having the marker allele from one parent or the other. The polymorphic TaPr-1 gene markers were then placed onto the previously assembled genetic linkage maps using the 'TRY' command in the Mapmaker V2.0 program for Macintosh (Lander et al 1987) as described in Abeysekara et al (2009). Mapped marker loci were given ''Xfcp'' designations according to the nomenclature assigned to the lab of J. Faris as outlined under the Reserved Laboratory Designators for Wheat DNA Probes, Primers, and Markers (http://wheat.pw.usda.…”