Response of TaFLR MAPKKK to wheat leaf rust and Fusarium head blight and the activation of downstream components

Mitogen-activated protein kinase pathways form a key network in plant defense responses. Gene array analysis has indicated that many members of the MAPK pathway in host plants are regulated in response to pathogen attack. TaFLR (wheat Fusarium and Leaf Rust Response, a wheat MAP kinase kinase kinase gene) was transcriptionally up-regulated during the early interactions of wheat and the leaf rust pathogen, Puccinia triticina. Infection with Fusarium graminearum also activated this kinase gene. Analysis of the background transcript levels in sixteen different wheat cultivars showed no correlation between the transcriptional level of TaFLR and the resistance phenotypes to Fusarium head blight. Transient expression of TaFLR in protoplasts activated pathogenesis-related genes β-1,3-glucanase and chitinase. While the level of TaFLRS gene (wheat Fusarium and Leaf Rust Sensitive, a wheat MAP kinase) remained unchanged at the translational level, the kinase protein was highly phosphorylated. Ectopic expression of TaFLR in tomato plants enhanced resistance against the bacterial pathogen Pseudomonas syringae pv. tomato. Our findings suggest that TaFLR may activate defense response pathways and this activation could involve the phosphorylation of TaFLRS.