Plant immunity suppression by an exo-β-1,3-glucanase and an elongation factor 1α of the rice blast fungus

Abstract

Fungal cell walls undergo continual remodeling that generates β-1,3-glucan fragments as products of endo-glycosyl hydrolases (GHs), which can be recognized as pathogen-associated molecular patterns (PAMPs) and trigger plant immune responses. How fungal pathogens suppress those responses is often poorly understood. Here, we study mechanisms underlying the suppression of β-1,3-glucan-triggered plant immunity by the blast fungus Magnaporthe oryzae. We show that an exo-β-1,3-glucanase of the GH17 family, named Ebg1, is important for fungal cell wall integrity and virulence of M. oryzae. Ebg1 can hydrolyze β-1,3-glucan and laminarin into glucose, thus suppressing β-1,3-glucan-triggered plant immunity. However, in addition, Ebg1 seems to act as a PAMP, independent of its hydrolase activity. This Ebg1-induced immunity appears to be dampened by the secretion of an elongation factor 1 alpha protein (EF1α), which interacts and co-localizes with Ebg1 in the apoplast. Future work is needed to understand the mechanisms behind Ebg1-induced immunity and its suppression by EF1α.

A Glycosyl Hydrolase 5 Family Protein Is Essential for Virulence of Necrotrophic Fungi and Can Suppress Plant Immunity

“…In fact, previous studies have shown that GH proteins were also involved in plant–pathogen interaction. For instance, Ebg1, as a glucanase in M. oryzae , can hydrolyze its own glucan, thereby achieving immune escape [ 33 ]. Interestingly, plants seem to have developed receptors capable of recognizing the GH family of proteins.…”

“…Interestingly, plants seem to have developed receptors capable of recognizing the GH family of proteins. Ebg1 also can be recognized by plants to trigger immune responses and cause cell death [ 33 ]. This is not an isolated example, XEG1 is important for virulence and can be recognized by plant RXEG1 as a PAMP and trigger intense cell death [ 29 , 30 , 44 ].…”

“…For instance, MoChia1 belonging to the GH18 family can not only regulate the growth of M. oryzae , but also binds to its own chitin to escape plant immunity during infection [ 32 ]. A GH17 extrafamily β-1,3-glucanase also can help M. oryzae escape plant recognition by hydrolyzing β-glucan during early infection [ 33 ]. These studies show that the mechanism of CWDEs in the process of pathogen infection is diversified.…”

Study of fungal cell wall evolution through its monosaccharide composition: An insight into fungal species interacting with plants

“…This is of particular interest for the fungal species described as plant endophytes, because the contribution of the cell wall components and ultrastructure in this process remains elusive. In addition, masking of cell wall polysaccharides may also be established by fungi that secret proteinaceous components known as effectors which may bind fungal cell wall carbohydrates to reduce its accessibility to host hydrolytic enzymes, or even enzymes that degrade oligosaccharides to monosaccharides, thus preventing the production of oligo-structures perceived by the host immune system ( Liu et al, 2023 , Sánchez-Vallet et al, 2015 , Wawra et al, 2016 ). Thus, we propose that chemical data should be complemented by in situ visualization of specific substructures (epitopes) localized among cell wall carbohydrates using suitably designed diverse molecular probes.…”

The Hidden Truths of Fungal Virulence and Adaptation on Hosts: Unraveling the Conditional Dispensability of Minichromosomes in the Hemibiotrophic Colletotrichum Pathogens

“…Fungal pathogens generate β-1,3-glucans for cell wall remodeling during plant infection, which, however can trigger pattern-triggered immunity (PTI). Recently, a CAZyme exo-β-1,3-glucanase (Ebg1) from the rice blast fungus Magnaporthe oryzae is reported to hydrolyze β-1,3-glucan, thereby suppressing PTI [ 21 ]. CGRA01v4_15032 , CGRA01v4_15038 and CGRA01v4_15051 encode unc-44/ankyrin proteins.…”