Cell walls are important interfaces of plant-fungal interactions, acting as robust physical and chemical barriers against invaders. Upon fungal colonization, plants deposit phenolics and callose at the sites of fungal penetration to prevent further fungal progression. Alterations in the composition of plant cell walls significantly impact host susceptibility. Furthermore, plants and fungi secrete glycan hydrolases acting on each other’s cell walls. These enzymes release various sugar oligomers into the apoplast, some of which activate host immunity via surface receptors. Recent characterization of cell walls from plant-colonizing fungi has emphasized the abundance of β-glucans in different cell wall layers, which makes them suitable targets for recognition. To characterize host components involved in immunity against fungi, we performed a protein pull-down with the biotinylated β-glucan laminarin. Thereby, we identified a plant glycoside hydrolase family 81-type glucan-binding protein (GBP) as a β-glucan interactor. Mutation of *GBP1* and its only paralog, *GBP2*, in barley led to decreased colonization by the beneficial root endophytes *Serendipita indica* and *S. vermifera*, as well as the arbuscular mycorrhizal fungus *Rhizophagus irregularis*. The reduction of colonization was accompanied by enhanced responses at the host cell wall, including an extension of callose-containing cell wall appositions. Moreover, *GBP* mutation in barley also reduced fungal biomass in roots by the hemibiotrophic pathogen *Bipolaris sorokiniana* and inhibited the penetration success of the obligate biotrophic leaf pathogen *Blumeria hordei*. These results indicate that GBP1 is involved in the establishment of symbiotic associations with beneficial fungi—a role that has potentially been appropriated by barley-adapted pathogens.
Cell walls are important interfaces of plant-fungal interactions, acting as robust physical and chemical barriers against invaders. Upon fungal colonization, plants deposit phenolics and callose at the sites of fungal penetration to prevent further fungal progression. Alterations in the composition of plant cell walls significantly impact host susceptibility. Furthermore, plants and fungi secrete glycan hydrolases acting on each other’s cell walls. These enzymes release various sugar oligomers into the apoplast, some of which activate host immunity via surface receptors. Recent characterization of cell walls from plant-colonizing fungi has emphasized the abundance of β-glucans in different cell wall layers, which makes them suitable targets for recognition. To characterize host components involved in immunity against fungi, we performed a protein pull-down with the biotinylated β-glucan laminarin. Thereby, we identified a plant glycoside hydrolase family 81-type glucan-binding protein (GBP) as a β-glucan interactor. Mutation of *GBP1* and its only paralog, *GBP2*, in barley led to decreased colonization by the beneficial root endophytes *Serendipita indica* and *S. vermifera*, as well as the arbuscular mycorrhizal fungus *Rhizophagus irregularis*. The reduction of colonization was accompanied by enhanced responses at the host cell wall, including an extension of callose-containing cell wall appositions. Moreover, *GBP* mutation in barley also reduced fungal biomass in roots by the hemibiotrophic pathogen *Bipolaris sorokiniana* and inhibited the penetration success of the obligate biotrophic leaf pathogen *Blumeria hordei*. These results indicate that GBP1 is involved in the establishment of symbiotic associations with beneficial fungi—a role that has potentially been appropriated by barley-adapted pathogens.
Wanke, A., van Boerdonk, S., Mahdi, L. K., Wawra, S., Neidert, M., Chandrasekar, B., Saake, P., Saur, I. M. L., Derbyshire, P., Holton, N., Menke, F. L. H., Brands, M., Pauly, M., Acosta, I. F., Zipfel, C., & Zuccaro, A. (2023). A GH81-type β-glucan-binding protein enhances colonization by mutualistic fungi in barley. Current biology : CB, 33(23), 5071–5084.e7. https://doi.org/10.1016/j.cub.2023.10.048
Wanke, A., van Boerdonk, S., Mahdi, L. K., Wawra, S., Neidert, M., Chandrasekar, B., Saake, P., Saur, I. M. L., Derbyshire, P., Holton, N., Menke, F. L. H., Brands, M., Pauly, M., Acosta, I. F., Zipfel, C., & Zuccaro, A. (2023). A GH81-type β-glucan-binding protein enhances colonization by mutualistic fungi in barley. Current biology : CB, 33(23), 5071–5084.e7. https://doi.org/10.1016/j.cub.2023.10.048
