The Arabidopsis leucine-rich repeat receptor kinase MIK2 is a crucial component of pattern-triggered immunity responses to Fusarium fungi

Fusarium is a genus of fungi causing severe economic damage in many crop species exemplified by Fusarium Head Blight of wheat or Panama Disease of banana. Plants sense immunogenic patterns (termed elicitors) at the cell surface contributing to disease resistance via the activation of pattern-triggered immunity (PTI). Knowledge of such elicitors or corresponding plant immunity components is largely lacking for Fusarium species. We describe a new peptide elicitor fraction present in several Fusarium spp. which elicits canonical PTI responses in Arabidopsis thaliana but depends on a currently unknown perception mechanism. We therefore employed a forward-genetics screen using Arabidopsis plants containing a cytosolic calcium reporter (apoaequorin) to isolate fere (Fusarium Elicitor Reduced Elicitation) mutants. The fere1 mutant showed impaired PTI marker responses to an enriched elicitor fraction derived from Fusarium oxysporum but normal responses to other fungal elicitors. We mapped the causal mutation to the receptor-like kinase MIK2 (MALE DISCOVERER1-INTERACTING RECEPTOR LIKE KINASE 2) with a hitherto undescribed role in PTI pathways but documented functions in other cell surface signalling pathways. The strength of the phenotype in fere1 and independent mik2 mutants supports that MIK2 is a new key component in sensing Fusarium. Fusarium elicitor responses also partially depend on PTI signalling components known for other cell surface elicitor responses such as BAK1, BIK1, PBL1, FERONIA, LLG1 and RBOHD. This shows that Arabidopsis senses Fusarium by a novel receptor complex at the cell surface that feeds into common PTI pathways and positions MIK2 as a central player that potentially integrates plant endogenous signals with biotic and abiotic stress responses.