Fungi secrete effectors during colonization of the host that are thought to contribute to disease development. We recently identified the Ecp6 effector from the tomato pathogen Cladosporium fulvum. Ecp6 contains LysM domains that are responsible for binding of chitin, the major constituent of fungal cell walls. During infection, Ecp6 sequesters chitin oligosaccharides that are released from the cell walls of invading hyphae to prevent elicitation of host immunity. This suppression of host immunity may represent a common strategy of host immune suppression by fungal pathogens, because LysM effectors are widely conserved in the fungal kingdom. These results were recently described in Science. We are presently characterizing LysM effectors from various plant pathogenic fungi, the full LysM effector catalogue of Verticillium, and LysM effectors from fungi that are not plant pathogens LysM effectors as extinguishers of host immunity. (a) Plant cells contain cell surface receptors (indicated by green sticks on the surface) to monitor the presence of potential pathogens (such as fungi, yellow) by means of pathogen-associated patterns (such as chitin, purple halo). (b) Perception of chitin oligosaccharides by chitin receptors results in the activation of an immune response (red lightning), and the pathogen (brown) is halted. (c) LysM effectors (yellow spheres) contribute to pathogen virulence by sequestering chitin oligosaccharides that thus no longer activate host chitin receptors. As a result, the host immune response is extinguished.
