A transcriptomic analysis of wheat lines that are resistant and susceptible to tan spot (Pyrenophora tritici-repentis) disease

Tan spot (TS), causal agent Pyrenophora tritici-repentis (Ptr), is a major threat to wheat production due to the lack of resistant cultivars. In our previous work, we identified MAGIC population parental lines exhibiting TS resistance and susceptibility, namely Robigus and Hereward, respectively. To understand the mechanisms underlying these phenotypes, we performed RNA-seq analysis of leaves before and during Ptr interaction. Principal component analysis suggested that infection of Hereward resulted in major shifts in the transcriptome but only minor changes were observed in the resistant line. When comparing mock- and Ptr-inoculated samples, differentially expressed genes (DEGs) were identified with DESeq2, leading to the targeting of 15,193 DEGs. Functional annotation showed the pathways enzyme classification, solute transport, RNA biosynthesis, protein modification and homeostasis represented 49.5% of DEGs in Robigus. Cellular metabolism pathways were induced, as well as vesicle trafficking, actin polymerization and cellulose. The upregulation of these cell wall related genes along with microscopic data suggested that barrier defense is a major feature of TS resistance in Robigus. Conversely, photosynthesis was the top fifth pathway in Hereward, totaling 389 repressed genes (12.63%). Photosynthesis collapse was linked to the activation of oligosaccharide metabolism and suppression of glycolysis, TCA cycle and amino acids degradation. This may reflect mobilization of host nutrients to Ptr. Our observations could inform wheat-breeding programs targeting TS resistance.

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