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

Abstract

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...

Immune elicitation by sensing the conserved signature from phytocytokines and microbes via theArabidopsisMIK2 receptor

“…Thus, Fusarium SCOOPLs trigger similar responses with Arabidopsis SCOOPs in a MIK2-dependent manner. This is consistent with the observation that the mik2 mutants were insensitive to the elicitor from different Fusarium spp 30. .…”

“…In addition, MIK2 plays a role in response to diverse environmental stresses, including cell wall integrity sensing, salt stress tolerance, and resistance to the soil-borne fungal pathogen Fusarium oxysporum [26][27][28][29] . A recent study suggested that MIK2 functions as a PRR perceiving an unknown peptide elicitor from F. oxysporum to activate plant immunity 30 . Here, we provide genetic and biochemical evidence that MIK2 is the bona fide receptor of SCOOP family peptides.…”

Biocontrol by Fusarium oxysporum Using Endophyte-Mediated Resistance

“…MAMP recognition is mediated by pattern recognition receptors (PRRs) located at the cell surface (Macho and Zipfel, 2014) such as the CERK1 chitin receptor of Arabidopsis (Miya et al, 2007). Forward genetics in Arabidopsis identified the receptor-like kinase MIK2 as a potential PRR and as a crucial component to recognize and respond to MAMPs from Fo (Coleman et al, 2019). PRRs are mainly expressed in root zones vulnerable to pathogen entry resulting in a heterogenic and tissue-specific responsiveness to different MAMPs (Chuberre et al, 2018).…”

“…PRRs are mainly expressed in root zones vulnerable to pathogen entry resulting in a heterogenic and tissue-specific responsiveness to different MAMPs (Chuberre et al, 2018). Responsiveness to chitin, for instance, is mostly confined to the mature zone and other parts of the root system are relatively insensitive to this MAMP and do not mount immune responses upon exposure to chitin (Millet et al, 2010;Coleman et al, 2019). This heterogeneity could explain why Fol typically does not penetrate mature root zones (Mes et al, 2000).…”

The Arabidopsis receptor kinase STRUBBELIG regulates the response to cellulose deficiency

“…The sub-1, qky-8 (all in Ler), and the sub-9 and qky-11 mutants (Col) have been characterized previously [44,47,50,51]. The prc1-1 [27], the1-1 [38], the1-6 [74], mik2-1 [39], mik2-3 [75], and ixr2-1 [30] alleles were also described previously. The sub-21 (Col) allele was generated using a CRISPR/Cas9 system in which the egg cell-specific promoter pEC1.2 controls Cas9 expression [76].…”