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

Abstract

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.

Computational prediction method to decipher receptor–glycoligand interactions in plant immunity

“…Then we applied the pipeline to predict binding of the DP4 oligomer to OsCEBiP, the rice chitin receptor, and its co‐receptor OsCERK1, and we found that the pipeline predicted OsCEBiP binding to the DP4 oligomer, but not to OsCERK1 (Figure S2), as described previously (Liu et al ., 2016). Next, we applied the pipeline to the fungal effectors Cf Avr4F and Mg1LysM, which bind to the DP6 chitin oligomer (Hurlburt et al ., 2018; Sánchez‐Vallet et al ., 2020), and we found that the model positively predicted their binding to the DP6 oligomer (Figure S2), further confirming the robustness of the pipeline developed (Figure 3).…”

“…Our in silico computational minimization procedure further supports these recent data. Similarly, the computational calculations performed here with rice OsCEBiP and OsCERK1 and some fungal effectors ( Cf Avr4 and Mg1LysM) that bind chitin (Figure S2) also confirmed published data (Liu et al ., 2016; Hurlburt et al ., 2018; Sánchez‐Vallet et al ., 2020) and supported the robustness of glycoligand/PRR binding predictions by the in silico computational minimization procedure described here. Remarkably, this technical advance might also allow the identification of key PRR residues involved in binding and stabilization of glycan structures, as shown here with the in silico validation of the relevance of Q109 and I141 from CERK1 in 1,4‐β‐ d ‐(GlcNAc) 6 binding (Figure S6).…”

“…In rice ( Oryza sativa ), the molecular mechanism of chitin recognition by the OsCEBiP receptor, a LysM‐PRR, has also been described (Liu et al ., 2016), and it has been shown that OsCERK1 cooperates with OsCEBiP module chitin‐mediated signaling (Shimizu et al ., 2010). Interestingly, LysM domains have also been described in some fungal effector proteins, like Cf Avr4F from Cladosporium fulvum and Mg1LysM from Zymoseptoria tritici , and their crystal structures have been obtained (Hurlburt et al ., 2018; Sánchez‐Vallet et al ., 2020). These fungal proteins bind chitin as a mechanism of fungal virulence aiming to avoid fungal perception by plant LysM‐PRRs.…”

Strategies to Manage Rice Sheath Blight: Lessons from Interactions between Rice and Rhizoctonia solani

“…Chitin, an unbranched homopolymer of 1, 4-β linked N-acetyl-D-glucosamine (GlcNAc), is the second most abundant polysaccharide on earth and is the major component of fungal cell walls. As a major pathogen-associated molecular pattern (PAMP) in rice, chitin is recognized by the pattern recognition receptor (PRR) CEBiP and coreceptor OsCERK1 on plant cell membrane, and thus initiating immune responses (Gong et al 2020 ; Sanchez-Vallet et al 2020 ; Shimizu et al 2010 ). For successful infection, fungal pathogens have evolved to secrete certain effector proteins to interfere with PAMP recognition by PRRs.…”

Adding by subtracting : Impairing tomato susceptibility genes to obtain resistance to Verticillium wilt

“…The selection of an effector to identify the corresponding effector target requires insights into the process a given effector is involved in. For example, effectors containing lysin motifs (LysMs), referred to as LysM effectors, were shown to perturb chitin-induced immunity by binding chitin through intermolecular LysM dimerization which protects fungal cell walls against host chitinases (Kombrink and Thomma, 2013;Sánchez-Vallet et al, 2020;Tian et al, 2020). Another example is the V. dahliae effector Avirulence on Ve1 tomato (Ave1).…”