Characterization of Heteropolysaccharides from Rhizoctonia Solani AG1 IA Cell Wall and Comparison of Their Effect on Inducing Plant Defense

Rhizoctonia solani (R. solani) is an important pathogenic fungus that causes symptoms of sheath blight, and the polysaccharide-rich cell wall plays a major role in plant-pathogen interactions. However, the composition and structure of its cell wall polysaccharides are insufficiently understood, and its specific function in plant-pathogen interactions is unknown, which makes effective control of sheath blight difficult at present. Herein, five cell wall polysaccharides (WF-1, WF-2, CAF-1, HAF-1 and HAF 2-1) were sequentially extracted by boiling water, cold and hot alkali from R. solani AG1 IA. They were heteropolysaccharides containing mainly glucose, mannose and galactose and less fucose, with molecular weights above 1100 kDa. These five polysaccharides mainly composed of-*4)-Glcp-(1-*,-*6)-Glcp-(1-*,-*4,6)-Glcp-(1-*,-*3,4)-Glcp-(1-*, and Manp-(1-*. Several polysaccharides, except WF-1, showed different induced resistance degrees on rice plant, with HAF 2-1 having the most significant effect. Further analysis using NMR confirmed that the backbone of HAF 2-1 mainly consisted of -*4)-a-D-Glcp- (1-* and-*6)-a-D-Glcp-(1-* with branches of-*4,6)-D-Glcp-(1-*. HAF 2-1 enhance the resistance of rice against R. solani through salicylic acid (SA)-mediated immune signaling pathway. This work improves our knowledge of the cell wall polysaccharides in plant pathogens and facilitates the study of pathogenic mechanisms and effective disease control.