Chitin, a polymer of N-acetylglucosamine, is an important structural component in the cell walls of fungal pathogens. Plant chitinases are capable of degrading this component to directly inhibit infection by fungal pathogens. Plants can further detect the chitin fragments released by chitinases to trigger additional defense responses. Recent studies have identified chitin receptors in different plant species and a number of downstream signaling components..
For more detail go through the link: