Identification and characterization of lectins and putative effector proteins in the interaction of endophytic fungi with roots

Molecular exchanges between fungi and plants are common events that result in either pathogenic or mutual beneficial interactions. The multitude of interspecies microbe-host relations that exist in ecosystems rely heavily on molecular cues that are transferred and sensed at the cellular level. These molecules can work and interact on the surface of the recipient cells but also some of them are able to cross cell membranes and have an intercellular function. A common term for proteins that are produced by a fungus and subsequently modulate the cellular function of the recipient host plant is effector. One class of potential effectors that is widespread among fungal species are lectin-like proteins which show a remarkable expansion within the genomes of the root endophytes Piriformospora indica and the closely related orchid mycorrhizal fungus Sebacina vermifera (Basidiomycota, Sebacinales) compared to other fungal genomes (Zuccaro et al., 2011; Lahrmann and Zuccaro 2012). Lectins are ubiquitous carbohydrate-binding proteins thought to be involved in symbiotic communication and plant immune system evasion. We are currently interested in identifying and characterising the biological function of novel beta glucan binding lectin-like proteins important for the symbiotic interaction between the root endophyte Piriformospora indica and its host plants barley and Arabidopsis thaliana. The ability of P. indica to colonize roots of a wide range of unrelated plants may depend, among others, on the evolution of strategies for host immune system evasion. The extensive beneficial effects of sebacinoid isolates and their ability to colonize Arabidopsis and several important crop plants offer many possible applications to improve plant performance. Understanding the underlying molecular mechanisms of these symbiosis-related genes will help us to understand if endophytes in a microbial community commonly use lectin-like proteins to facilitate root colonization and if these mechanism are therefore an important component of this complex trait. In the long run this work will contribute to our knowledge on plant-fungus interactions and in plant defense mechanisms and it might lead to novel strategies for the control of pathogenic fungi and the production of resistant plants.