AUTHOR=Downie Rowena C. , Bouvet Laura , Furuki Eiko , Gosman Nick , Gardner Keith A. , Mackay Ian J. , Campos Mantello Camila , Mellers Greg , Phan Huyen T. T. , Rose Gemma A. , Tan Kar-Chun , Oliver Richard P. , Cockram James 

TITLE=Assessing European Wheat Sensitivities to Parastagonospora nodorum Necrotrophic Effectors and Fine-Mapping the Snn3-B1 Locus Conferring Sensitivity to the Effector SnTox3

JOURNAL=Frontiers in Plant Science

VOLUME=9

YEAR=2018

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2018.00881

DOI=10.3389/fpls.2018.00881

ISSN=1664-462X

ABSTRACT=<p><italic>Parastagonospora nodorum</italic> is a necrotrophic fungal pathogen of wheat (<italic>Triticum aestivum</italic> L.), one of the world’s most important crops. <italic>P. nodorum</italic> mediates host cell death using proteinaceous necrotrophic effectors, presumably liberating nutrients that allow the infection process to continue. The identification of pathogen effectors has allowed host genetic resistance mechanisms to be separated into their constituent parts. In <italic>P. nodorum</italic>, three proteinaceous effectors have been cloned: <italic>SnToxA</italic>, <italic>SnTox1</italic>, and <italic>SnTox3</italic>. Here, we survey sensitivity to all three effectors in a panel of 480 European wheat varieties, and fine-map the wheat SnTox3 sensitivity locus <italic>Snn3-B1</italic> using genome-wide association scans (GWAS) and an eight-founder wheat multi-parent advanced generation inter-cross (MAGIC) population. Using a Bonferroni corrected <italic>P</italic> ≤ 0.05 significance threshold, GWAS identified 10 significant markers defining a single locus, <italic>Snn3-B1</italic>, located on the short arm of chromosome 5B explaining 32% of the phenotypic variation [peak single nucleotide polymorphisms (SNPs), Excalibur_c47452_183 and GENE-3324_338, -log<sub>10</sub><italic>P</italic> = 20.44]. Single marker analysis of SnTox3 sensitivity in the MAGIC population located <italic>Snn3-B1</italic> via five significant SNPs, defining a 6.2-kb region that included the two peak SNPs identified in the association mapping panel. Accordingly, SNP Excalibur_c47452_183 was converted to the KASP genotyping system, and validated by screening a subset of 95 wheat varieties, providing a valuable resource for marker assisted breeding and for further genetic investigation. In addition, composite interval mapping in the MAGIC population identified six minor SnTox3 sensitivity quantitative trait loci, on chromosomes 2A (<italic>QTox3.niab-2A.1, P-</italic>value = 9.17<sup>-7</sup>), 2B (<italic>QTox3.niab-2B.1</italic>, <italic>P</italic> = 0.018), 3B (<italic>QTox3.niab-3B.1</italic>, <italic>P</italic> = 48.51<sup>-4</sup>), 4D (<italic>QTox3.niab-4D.1</italic>, <italic>P</italic> = 0.028), 6A (<italic>QTox3.niab-6A.1, P</italic> = 8.51<sup>-4</sup>), and 7B (<italic>QTox3.niab-7B.1</italic>, <italic>P</italic> = 0.020), each accounting for between 3.1 and 6.0 % of the phenotypic variance. Collectively, the outcomes of this study provides breeders with knowledge and resources regarding the sensitivity of European wheat germplasm to <italic>P. nodorum</italic> effectors, as well as simple diagnostic markers for determining allelic state at <italic>Snn3-B1</italic>.</p>