Integrated metabolo-transcriptomics and functional characterization reveals that the wheat auxin receptor TIR1 negatively regulates defense against Fusarium graminearum

Fusarium head blight(FHB) caused by Fusarium graminearum Schwabe(teleomorph Gibberella zeae(Schw.) Perch) results in large yield losses in annual global wheat production. Although studies have identified a number of wheat FHB resistance genes,a deeper understanding of the mechanisms underlying host plant resistance to F. graminearum is required for the control of FHB. Here, an integrated metabolomics and transcriptomics analysis of infected wheat plants(Triticum aestivum L.) enabled identification of 789 differentially accumulated metabolites, including flavonoids, phenolamides, tryptamine derivatives, and phytohormones, and revealed altered expression of more than 100 genes that function in the biosynthesis or regulation of these pathways. Our data regarding the effects of F. graminearum infection on flavonoids and auxin signaling led to follow-up experiments that showed that exogenous kaempferide and apigenin application on spikes increased wheat resistance to FHB,while exogenous auxin treatment increased FHB susceptibility. RNAi-mediated knockdown of the gene encoding the auxin receptor, Ta TIR1, increased FHB resistance. Our data supported the use of Ta TIR1 knockdown in controlling FHB. Our study provides insights on the wheat response to F.graminearum infection and its FHB resistance mechanisms while illustrating the potential of Ta TIR1 knockdown in increasing FHB resistance during crop improvement programs.