RESUMEN
Immune responses in plants are triggered by molecular patterns or elicitors, recognized by plant pattern recognition receptors. Such molecular patterns are consequence of host-pathogen interactions and the response cascade activated after their perception is known as pattern-triggered immunity (PTI). Glucans have emerged as key players in PTI, but the ability of certain glucans to stimulate defensive responses in plants remains understudied. This work focused on identifying novel glucan oligosaccharides as molecular patterns. The ability of various microorganism-derived glucans to prompt PTI responses was tested, revealing that specific microbial-derived molecules, such as short linear ß-1,2-glucans, trigger this response in plants by increasing the production of reactive oxygen species (ROS), MAP kinase phosphorylation, and differential expression of defence-related genes in Arabidopsis thaliana. Pretreatments with ß-1,2-glucan trisaccharide (B2G3) improved Arabidopsis defence against bacterial and fungal infections in a hypersusceptible genotype. The knowledge generated was then transferred to the monocotyledonous model species maize and wheat, confirming that these plants also respond to ß-1,2-glucans, with increased ROS production and improved protection against fungal infections following B2G3 pretreatments. In summary, as with other ß-glucans, plants perceive ß-1,2-glucans as warning signals and stimulate defence responses against phytopathogens.
RESUMEN
Every fungal cell is encapsulated in a cell wall, essential for cell viability, morphogenesis, and pathogenesis. Most knowledge of the cell wall composition in fungi has focused on ascomycetes, especially human pathogens, but considerably less is known about early divergent fungal groups, such as species in the Zoopagomycota and Mucoromycota phyla. To shed light on evolutionary changes in the fungal cell wall, we studied the monosaccharide composition of the cell wall of 18 species including early diverging fungi and species in the Basidiomycota and Ascomycota phyla with a focus on those with pathogenic lifestyles and interactions with plants. Our data revealed that chitin is the most characteristic component of the fungal cell wall, and was found to be in a higher proportion in the early divergent groups. The Mucoromycota species possess few glucans, but instead have other monosaccharides such as fucose and glucuronic acid that are almost exclusively found in their cell walls. Additionally, we observed that hexoses (glucose, mannose and galactose) accumulate in much higher proportions in species belonging to Dikarya. Our data demonstrate a clear relationship between phylogenetic position and fungal cell wall carbohydrate composition and lay the foundation for a better understanding of their evolution and their role in plant interactions.