ARS | Publication request: Two Putatively Homoeologous Wheat Genes Mediate Recognition of SnTox3 to Confer Effector-triggered Susceptibility to Stagonospora nodorum

Submitted to: Plant Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 5, 2010
Publication Date: January 5, 2011
Citation: Zhang, Z., Friesen, T.L., Xu, S.S., Shi, G., Liu, Z., Rasmussen, J., Faris, J.D. 2011. Two Putatively Homoeologous Wheat Genes Mediate Recognition of SnTox3 to Confer Effector-triggered Susceptibility to Stagonospora nodorum. Plant Journal. 65:27-38.

Interpretive Summary: The pathogen Stagonospora nodorum produces multiple components known as effectors that are recognized by specific genes in wheat, and recognition of an effector by a specific wheat gene results in the development of the disease Stagonospora nodorum blotch (SNB). In this study, a novel gene that recognized the effector SnTox3 was identified in Aegilops tauschii, a wild ancestor of common wheat. The gene, designated Snn3-D1, was located to the short arm of chromosome 5D. Previous research showed that SnTox3 is recognized by the Snn3-B1 gene on wheat chromosome 5B, which is homoeologous (related by ancestry) to chromosome 5D. Here, we showed that Snn3-B1 and Snn3-D1 not only both recognized SnTox3 to confer SNB, but they also lie within homoeologous positions along their respective chromosomes indicating that they were likely derived from a common ancestor. The presence of the Snn3-D1 gene resulted in a stronger disease reaction compared to Snn3-B1 indicating that the two genes are not functionally identical. Genomic analysis was used to target the Snn3-D1 gene with molecular markers, which provides useful tools for plant breeders to eliminate the gene from breeding material and for initiating the molecular characterization of the gene.

Technical Abstract: The pathogen Stagonospora nodorum produces multiple virulence effectors, also known as host-selective toxins (HSTs), that interact with corresponding host sensitivity genes in an inverse gene-for-gene manner to cause the disease Stagonospora nodorum blotch (SNB) in wheat. In this study, a novel sensitivity gene was identified in Aegilops tauschii, the diploid D-genome donor of common wheat. The gene was mapped to the short arm of chromosome 5D and mediated recognition of the effector SnTox3, which was previously shown to be recognized by the wheat gene Snn3 on chromosome arm 5BS. Comparative mapping suggested that Snn3 and the gene on 5DS are homoeologous and thus derived from a common ancestor. Therefore, we propose to designate these genes as Snn3-B1 and Snn3-D1, respectively. Compatible Snn3-D1-SnTox3 interactions resulted in more severe necrosis in both effector infiltration and spore inoculation experiments compared to compatible Snn3-B1-SnTox3 interactions indicating that Snn3-B1 and Snn3-D1 may have different levels of affinity for SnTox3 recognition. Wheat bin-mapped ESTs and good levels of colinearity among the wheat Snn3 regions, rice, and Brachypodium were exploited for saturation and fine mapping of the Snn3-D1 locus. Markers delineating the Snn3-D1 locus to a 1.4 cM interval will be useful for marker-assisted selection and to initiate positional cloning. This is the first report of homoeologous genes mediating recognition of the same pathogen effector. Further characterization of these interactions will enhance our knowledge regarding the exploitation of host mechanisms by necrotrophic pathogens to cause disease.