Genetically dissect disease interactions between Parastagonospora nodorum and wheat (Triticum aestivum L.)
Parastagonospora nodorum is a necrotrophic fungal pathogen of wheat (Triticum aestivum L.) and the causative agent of stagonospora nodorum blotch (SNB). P. nodorum mediates host cell death using proteinaceous effectors. Three P. nodorum effectors have been cloned: SnToxA, SnTox1 and SnTox3. SnTox3 susceptible wheat cultivars possess a dominant susceptibility allele at the Snn3-B1 locus; breeding to remove SnTox3 sensitivity could help increase P. nodorum disease resistance. The research presented here falls into three main areas: 1. Genetic mapping of SnTox3 sensitivity: the major SnTox3 sensitivity locus Snn3-B1 was fine-mapped using an association mapping panel, the Avalon x Cadenza population and a MAGIC population. These defined a 6.2 kb region on chromosome 5B explaining ≥ 32 % of the phenotypic variation. The most significantly associated SNP was converted to a KASP marker. Additionally, nine minor SnTox3 sensitivity QTL were identified on chromosomes 1B, 2A, 2B, 3B, 4D, 6A, 6B, and 7B, each accounting for 2.6-6.0 % of the phenotypic variation. 2. Gene expression analysis: combining RNA-seq and genomic analysis in a time-course experiment using a SnTox3 sensitive (Cadenza) and insensitive variety (Avalon), two treatments (+/- SnTox3 infiltration) and 0, 4, 8, 12, and 24 hour time-points allowed investigation of gene expression before and after SnTox3 infiltration. Two Snn3-B1 candidate genes were identified, a protein kinase and wall-associated kinase, with analysis of genome-wide patterns of gene expression providing insights into the molecular mechanism of the SnTox3-Snn3-B1 pathway. 3. Adult plant resistance: The Avalon x Cadenza bi-parental population was used to investigate adult plant P. nodorum resistance. First, an improved Avalon x Cadenza genetic map was developed using publicly available genotype data. This was combined with field trial data to identify a major QTL on chromosome 5A for leaf and glume blotch and a further seven QTL on chromosomes 1B, 2D, 3B, 5A, 5B and 7B. Of these, field resistance QTL were found to co-locate with the effector sensitivity QTL Snn1 and Snn7. Collectively, this research provides wheat breeders and researchers with knowledge and molecular resources regarding sensitivity to the P. nodorum effector, SnTox3, as well as field QTL for both leaf and glume blotch.
wheat, parastagonospora nodorum, stagonospora, nodorum, blotch, disease, triticum aestivum, effector
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