Figure 6.

Model for the production and function of the conserved fungal EPS-derived β-1,3;1,6-glucan decasaccharide. The fungal-responsive GH17 family member HvBGLUII is found in the apoplast of barley roots and acts on β-1,3-glucan. Digestion of linear β-1,3-glucan (laminariheptaose) with HvBGLUII enhances ROS accumulation in barley roots, corroborating its role as a host defense enzyme with a function in β-glucan perception. To counteract the activity of HvBGLUII, plant-colonizing fungi produce a β-1,3;1,6-glucan-rich EPS matrix. The activity of HvBGLUII on the EPS matrix releases a conserved β-GD, which is resilient to further digestion by GH17 family members. The β-GD acts as a carbohydrate-class effector by scavenging ROS and enhancing fungal colonization. Lectins containing WSC domains are enriched in the outer EPS matrix and lectins containing LsyM domains are enriched in the CW of S. indica. Graphical illustration was designed with the BioRender online tool.