Functional analysis of LysM effectors secreted by fungal plant pathogens

Chitin is a homopolymer of N-acetyl-d-glucosamine (GlcNAc)that is abundantly present in nature and found as a major structural component in the fungal cell wall. In Chapter 1,the role of chitin as an important factor in the interaction between fungal pathogens and their plant hosts is discussed. As plants do not produce chitin, they evolved to recognize fungal chitin as a non-self molecule by plasma membrane receptors that can activate host immune responses to stop fungal growth.To overcome those host immune responses, fungal pathogens secrete effector molecules that manipulate host physiology, including immune responses, to support colonization. The chitin-binding Lysin motif (LysM) effector Ecp6 from the fungal tomato pathogen Cladosporium fulvumwas previously demonstrated to contribute to virulence through interfering with the activation of chitin-induced host immune responses. Subsequently, LysM effector genes were found in the genomes of many fungal species. In Chapter 2 we describe the functional characterization of LysM effectors of the plant pathogenic fungi Mycosphaerella graminicola, Magnaporthe oryzae and Colletotrichum higginsianum, which cause leaf blotch disease of wheat, rice blast disease and anthracnose disease on Brassicaceae, respectively. This functional analysis revealed that the ability to perturb chitin-induced immunity is conserved among LysM effectors of these fungal plant pathogens. In addition, two LysM effectors that are secreted by M. graminicolawere found to protect fungal hyphae against cell wall hydrolytic enzymes from plants, demonstrating that LysM effectors can contribute to virulence of fungal plant pathogens in multiple ways. The M. graminicola LysM effector Mg3LysM and C. fulvum Ecp6 both contain three LysM domains and show a high overall similarity. However, whereas Mg3LysM can protect fungal hyphae against plant-derived cell wall hydrolytic enzymes, Ecp6 does not have this capacity. Chapter 3describes a functional analysis of