Cell wall α-1,3-glucans from a biocontrol isolate of Rhizoctonia: immunocytolocalization and relationship with α-glucanase activity from potato sprouts

The interface between plants and pathogens plays an important role in their interaction. Studies of fungal cell walls are scarce and previous results show the existence of α-1,3-glucans in addition to ß-glucans. In addition, α-1,3-glucans are not present in plant cell walls, and α-glucanase activity in plants has not been described before. In a previous work, we purified and characterized an α-1,3-glucan from a binucleated, non-pathogenic Rhizoctonia isolate, which induces plant defence responses. Therefore, in order to study the architecture of the fungal cell wall, and the accessibility and localization of the α-glucan elicitor, we prepared an antibody against the α-1,3-glucan and analysed its localization by TEM. Immunolocalization showed the presence of the α-1,3-glucan in the intercellular spaces and along the cell walls, mainly on the inner layers. This result, and the presence of the α-1,3-glucan in the liquid culture medium in which binucleated non-pathogenic Rhizoctonia was grown, confirmed that the α-glucan had been secreted. The α-1,3-glucan was also immunocytolocalized on potato sprouts tissue elicited with the glucan; gold particles were observed in vacuoles and close to the plasmalemma. In addition, α-glucanase activity in potato sprouts was detected using cell wall glucans from the pathogenic isolate R. solani AG-3 as substrates; whereas, when cell wall glucans from non-pathogenic isolates were used, no α-glucanase activity was detected. Our results suggest that the presence of α-1,3-glucans could be associated with the formation and integrity of the cell wall and also with plant–fungi interactions. This is the first report to describe α-glucanolytic activity in plants.