Abstract
Lysin motif (LysM) modules are approximately 50 amino acids long and bind to peptidoglycan, chitin and its derivatives. Certain LysM proteins in plant pathogenic and entomopathogenic fungi are shown to scavenge chitin oligosaccharides and thereby dampen host defense reactions. Other LysM proteins can protect the fungal cell wall against hydrolytic enzymes. In this study, we investigated the biological function of LysM proteins in the mycoparasitic fungus Clonostachys rosea. The C. rosea genome contained three genes coding for LysM-containing proteins and gene expression analysis revealed that lysm1 and lysm2 were induced during mycoparasitic interaction with Fusarium graminearum and during colonization of wheat roots. Lysm1 was suppressed in germinating conidia, while lysm2 was induced during growth in chitin or peptidoglycan-containing medium. Deletion of lysm1 and lysm2 resulted in mutants with increased levels of conidiation and conidial germination, but reduced ability to control plant diseases caused by F. graminearum and Botrytis cinerea. The Δlysm2 strain showed a distinct, accelerated mycelial disintegration phenotype accompanied by reduced biomass production and hyphal protection against hydrolytic enzymes including chitinases, suggesting a role of LYSM2 in hyphal protection against chitinases. The Δlysm2 and Δlysm1Δlysm2 strains displayed reduced ability to colonize wheat roots, while only Δlysm1Δlysm2 failed to suppress expression of the wheat defense response genes PR1 and PR4. Based on our data, we propose a role of LYSM1 as a regulator of fungal development and of LYSM2 in cell wall protection against endogenous hydrolytic enzymes, while both are required to suppress plant defense responses. Our findings expand the understanding of the role of LysM proteins in fungal-fungal interactions and biocontrol.
Highlights
Lysin motif (LysM) domains are approximately 50 amino acids long family 50 carbohydratebinding modules (CBM50) that bind to N-acetylglucosamine (GlcNAc)-containing glycans such as peptidoglycan, chitin and chitin-like compounds (Buist et al, 2008)
LysM modules are found in various proteins including hydrolytic enzymes like peptidoglycan hydrolases, peptidases, chitinases, esterases and nucleotidases, as well as in adhesins required for cell growth and division, autolysis, and virulence (Buist et al, 2008)
By generating and analyzing gene deletion and complementation strains, we demonstrate a role of LysM proteins in regulating fungal development and autolysis, in biological control of plant pathogens, in suppression of plant host defense response and in root colonization
Summary
Lysin motif (LysM) domains are approximately 50 amino acids long family 50 carbohydratebinding modules (CBM50) that bind to N-acetylglucosamine (GlcNAc)-containing glycans such as peptidoglycan, chitin and chitin-like compounds (Buist et al, 2008). LysMs are present in certain cell surface receptor kinases and recognize chitin, peptidoglycan and their derivatives (Antolín-Llovera et al, 2014), which are essential structural components of the fungal and bacterial cell wall, respectively They are a well-established microbe-associated molecular pattern (MAMP) in fungi and bacteria. LysM modules are present in plants’ Nod factor receptors and Myc factor receptors that bind Nod factors from symbiotic rhizobia and Myc factors from symbiotic arbuscular mycorrhizal fungi, respectively Detection of these compounds by transmembrane LysM-containing protein receptors of host plants activate MAMP-triggered defense signaling, against bacterial and fungal pathogens, and symbiotic signaling during interactions between legume plants and nitrogen-fixing bacteria and arbuscular mycorrhiza (Antolín-Llovera et al, 2014)
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