Revisiting chitinases and β-1,3-glucanases as tools for plant protection

Plants have evolved an immune system consisting of receptor proteins

which, upon activation by pathogen-derived molecules, initiate a cascade of immune responses that trigger changes in host gene expression. Among the up-regulated genes are many hydrolytic enzymes including chitinases and glucanases that catalyze the degradation of the carbohydrate polymers chitin and glucan, respectively. As healthy plants do not contain chitin it was proposed that plant chitinases act as defensive weapons that target the chitin present in their fungal pathogens and insect pests. Indeed plant chitinases were shown to have antifungal activity. However, attempts to increase plant disease resistance via enhanced expression of plant chitinases were not very effective. This may be explained by the recent finding that fungal pathogens have evolved effector proteins that target plant chitinases and glucanases to render them less efficient. Here we propose to test whether chitinases and glucanases of fungal origin can protect plants from attack by fungal pathogens. In contrast to plant chitinases belonging to glycoside hydrolase class GH19, fungal chitinases belong to the structurally different class GH18. Hence, pathogen effectors are not expected to interfere directly with fungal chitinases. As a source of fungal chitinases and glucanases we propose Coprinus species that show at maturation a spectacular autolysis of their fruiting body. Within a few hours the rather large Coprinus fruiting body is dissolved into an inky liquid demonstrating that Coprinus contains highly active hydrolytic enzymes. In summary, we hypothesize that Coprinus chitinases and glucanases are well suited to protect plants from fungal pathogens because a) they likely have a higher substrate affinity and/or enzymatic activity than plant the plant enzymes and b) their activity is unlikely to be inhibited by pathogen effectors. The aim of the project is to test this hypothesis.