Integrated transcriptome and hormone profiling highlight the role of multiple phytohormone pathways in wheat resistance against fusarium head blight

Multiple molecular tools and assays were deployed to compare the resistant variety Sumai3 with three regionally adapted Canadian cultivars, Stettler, Muchmore and FL62R1. Macroscopic and microscopic disease evaluation established the relative level of Type II FHB resistance of the four varieties and revealed that the F. graminearum (Fg) infection process displayed substantial temporal differences among organs. The rachis was found to play a critical role in preventing Fg spread within spikes. Large-scale, organ-specific RNA-seq at different times after Fg infection demonstrated that diverse defense mechanisms were expressed faster and more intensely in the spikelet of resistant varieties. The roles of plant hormones during the interaction of wheat with Fg was inferred based on the transcriptomic data obtained and the quantification of the major plant hormones. Salicylic acid and jasmonic acid were found to play predominantly positive roles in FHB resistance, whereas auxin and ABA were associated with susceptibility, and ethylene appeared to play a dual role during the interaction with Fg. The four genotypes were subjected to challenge by the pathogenic fungus Fusarium graminearum or with 10 μl ddH2O as a mock treatment. Samples inoculated with Fg were taken at 1, 2, 3 days post inoculation (dpi) from spikelets and 2, 3, 4 dpi from rachis. Samples treated with water were harvested at 2 days post treatment from spikelets and rachis.