Biology subjects

Kombrink, A.

Publications and source records attributed to Kombrink, A..

3 recordsLinked to original sources

bioRxiv2020

Fungal LysM effectors that comprise two LysM domains bind chitin through intermolecular dimerization

Chitin is a homopolymer of {beta}-(1,4)-linked N-acetyl-D-glucosamine (GlcNAc) and a major structural component of fungal cell walls. In plants, chitin acts as a microbe-associated molecular pattern (MAMP) that is recognized by lysin motif (LysM)-containing plant cell surface-localized pattern recognition receptors (PRRs) that activate a plethora of downstream immune responses. In order to deregulate chitin-induced plant immunity and successfully establish infection, many fungal pathogens secrete LysM domain-containing effector proteins during host colonization. It was previously shown that the LysM effector Ecp6 from the tomato leaf mould fungus Cladosporium fulvum can outcompete plant PRRs for chitin binding because two of its three LysM domains cooperate to form a composite groove with ultra-high (pM) chitin-binding affinity. However, most functionally characterized LysM effectors contain only two LysMs, including Magnaporthe oryzae MoSlp1, Verticillium dahliae Vd2LysM, and Colletotrichum higginsianum ChElp1 and ChElp2. Here, we performed modelling, structural and functional analyses to investigate whether such dual-domain LysM effectors can also form ultra-high chitin-binding affinity grooves through intramolecular LysM dimerization. However, our study suggests that intramolecular LysM dimerization does not occur. Rather, our data support the occurrence of intermolecular LysM dimerization for these effectors, associated with a significantly lower chitin binding affinity than monitored for Ecp6. Interestingly, the intermolecular LysM dimerization allows for the formation of polymeric complexes in the presence of chitin. Possibly, such polymers may precipitate at infection sites in order to eliminate chitin oligomers, and thus suppress the activation of chitin-induced plant immunity.

plant biology↗

bioRxiv2019

A secreted LysM effector protects fungal hyphae through chitin-dependent homodimer polymerization

Plants trigger immune responses upon recognition of fungal cell wall chitin, followed by the release of various antimicrobials, including chitinase enzymes that hydrolyze chitin. In turn, many fungal pathogens secrete LysM effectors that prevent chitin recognition by the host through scavenging of chitin oligomers. We previously showed that intrachain LysM dimerization of the Cladosporium fulvum effector Ecp6 confers an ultrahigh-affinity binding groove that competitively sequesters chitin oligomers from host immune receptors. Additionally, particular LysM effectors are found to protect fungal hyphae against chitinase hydrolysis during host colonization. However, the molecular basis for the protection of fungal cell walls against hydrolysis remained unclear. Here, we determined a crystal structure of the single LysM domain-containing effector Mg1LysM of the wheat pathogen Zymoseptoria tritici and reveal that Mg1LysM is involved in the formation of two kinds of dimers; a chitin-dependent dimer as well as a chitin-independent homodimer. In this manner, Mg1LysM gains the capacity to form a supramolecular structure by chitin-induced oligomerization of chitin-independent Mg1LysM homodimers, a property that confers protection to fungal cell walls against host chitinases.

microbiology↗

bioRxiv2016

Verticillium dahliae LysM effectors differentially contribute to virulence on plant hosts

Chitin-binding LysM effectors contribute to virulence of various plant pathogenic fungi that are causal agents of foliar diseases. Here, we report on LysM effectors of the soil-borne fungal vascular wilt pathogen Verticillium dahliae. Comparative genomics revealed three core LysM effectors that are conserved in a collection of V. dahliae strains. Remarkably, and in contrast to the previously studied LysM effectors of other plant pathogens, no expression of core LysM effectors was monitored in planta in a taxonomically diverse panel of host plants. Moreover, targeted deletion of the individual LysM effector genes in V. dahliae strain JR2 did not compromise virulence in infections on Arabidopsis, tomato or Nicotiana benthamiana. Interestingly, an additional lineage-specific LysM effector is encoded in the genome of V. dahliae strain VdLs17 but not in any other V. dahliae strain sequenced to date. Remarkably, this lineage-specific effector is expressed in planta and contributes to virulence of V. dahliae strain VdLs17 on tomato, but not on Arabidopsis or on N. benthamiana. Functional analysis revealed that this LysM effector binds chitin, is able to suppress chitin-induced immune responses, and protects fungal hyphae against hydrolysis by plant hydrolytic enzymes. Thus, in contrast to the core LysM effectors of V. dahliae, this lineage-specific LysM effector of strain VdLs17 contributes to virulence in planta.

plant biology↗