Summary Fusarium spp. cause severe economic damage in many crops, exemplified by Panama disease of banana or Fusarium head blight of wheat. Plants sense immunogenic patterns (termed elicitors) at the cell surface to initiate pattern‐triggered immunity (PTI). Knowledge of fungal elicitors and corresponding plant immune‐signaling is incomplete but could yield valuable sources of resistance. We characterized Arabidopsis thaliana PTI responses to a peptide elicitor fraction present in several Fusarium spp. and employed a forward‐genetic screen using plants containing a cytosolic calcium reporter to isolate fusarium elicitor reduced elicitation (fere) mutants. We mapped the causal mutation in fere1 to the leucine‐rich repeat receptor‐like kinase MDIS1‐INTERACTING RECEPTOR‐LIKE KINASE 2 (MIK2) and confirmed a crucial role of MIK2 in fungal elicitor perception. MIK2‐dependent elicitor responses depend on known signaling components and transfer of AtMIK2 is sufficient to confer elicitor sensitivity to Nicotiana benthamiana. Arabidopsis senses Fusarium elicitors by a novel receptor complex at the cell surface that feeds into common PTI pathways. These data increase mechanistic understanding of PTI to Fusarium and place MIK2 at a central position in Arabidopsis elicitor responses.

Little is known about plant genetic and biochemical components that coordinate immune responses with growth and environmental cues. C-TERMINALLY ENCODED PEPTIDEs (CEPs) control plant development and nitrogen demand signaling. Here, we identified CEP4 as an immune-modulatory peptide (phytocytokine) in Arabidopsis thaliana. CEP4 and related CEPs are important regulators of resistance to plant pathogenic bacteria and are perceived by the tissue-specific receptor kinases CEP RECEPTOR 1 (CEPR1), CEPR2 and the phylogenetically related RECEPTOR-LIKE KINASE 7 (RLK7). CEP4 promotes flagellin-triggered responses and we provide evidence that CEPs modulate cell surface immunity upon N limitation. We propose that CEPs integrate biotic and abiotic stress-associated signals to safeguard plant health.

8Fusarium is a genus of fungi causing severe economic damage in many crop species exemplified 9by Fusarium Head Blight of wheat or Panama Disease of banana. Plants sense immunogenic patterns 10 (termed elicitors) at the cell surface contributing to disease resistance via the activation of pattern-11 triggered immunity (PTI). Knowledge of such elicitors or corresponding plant immunity components is 12 largely lacking for Fusarium species. We describe a new peptide elicitor fraction present in several 13 Fusarium spp. which elicits canonical PTI responses in Arabidopsis thaliana but depends on a currently 14 unknown perception mechanism. We therefore employed a forward-genetics screen using Arabidopsis 15 plants containing a cytosolic calcium reporter (apoaequorin) to isolate fere (Fusarium Elicitor Reduced 16 Elicitation) mutants. The fere1 mutant showed impaired PTI marker responses to an enriched elicitor 17 fraction derived from Fusarium oxysporum but normal responses to other fungal elicitors. We mapped 18 the causal mutation to the receptor-like kinase MIK2 (MALE DISCOVERER1-INTERACTING 19 RECEPTOR LIKE KINASE 2) with a hitherto undescribed role in PTI pathways but documented 20 functions in other cell surface signalling pathways. The strength of the phenotype in fere1 and 21 independent mik2 mutants supports that MIK2 is a new key component in sensing Fusarium. Fusarium 22 elicitor responses also partially depend on PTI signalling components known for other cell surface 23 elicitor responses such as BAK1, BIK1, PBL1, FERONIA, LLG1 and RBOHD. This shows that 24 Arabidopsis senses Fusarium by a novel receptor complex at the cell surface that feeds into common 25 PTI pathways and positions MIK2 as a central player that potentially integrates plant endogenous signals 26 with biotic and abiotic stress responses. 27Plants have evolved diverse pattern-recognition receptors (PRRs) at the cell surface to detect 32 microbial invaders and form multipartite PRR complexes to initiate and regulate intracellular signalling 33 pathways. Molecular patterns from diverse origins (self or non-self; collectively termed elicitors) can be 34 perceived by plant PRRs contributing to quantitative disease-resistance via the activation of pattern-35 triggered immunity (PTI). Fusarium is a large genus of fungi causing severe economic damage in many 36 cultivated plant species and although several studies have demonstrated mechanisms to detect and 37 respond to Fusarium, knowledge of elicitors from Fusarium or subsequently induced plant immune-38 signalling is sparse. To improve mechanistic understanding of Fusarium-triggered PTI, we employed a 39 forward-genetics screen in Arabidopsis to isolate a mutant strongly impaired in PTI responses to an 40 elicitor fraction from Fusarium spp. but fully responding to other fungal elicitors. We identified a causal 41 mutation in the leucine-rich repeat receptor kinase MIK2 (MDIS1-INTERACTING RECEPTOR LIKE 42 KINASE2), which was previously described in the context of abiotic and biotic stress resis...