Review accepted: Chitins and Chitosans - A Tale of Discovery and Disguise, of Attachment and Attainment

Today, the review on chitosans in the cell walls of phytopathogenic fungi written by Mounashree Student, Margareta Hellmann, Dr. Stefan Cord-Landwehr and Prof. Bruno Moerschbacher was accepted for publication. We had been invited to contribute this review to next year’s volume of “Current Opinion in Plant Biology”. Based on our observation of chitosan in the cell walls of the endophytic mycelium of the wheat stem rust fungus and some other fungi, we had put forward – already more than 20 years ago! – the molecular stealth hypothesis which assumes that pathogenic fungi may convert the chitin in their cell walls into chitosan to escape the chitin-triggered immune system of their hosts. This hypothesis has been widely accepted, including for human-pathogenic fungi, but knock-out experiments in pathogenic fungi deleting chitin deacetylases and, thus, preventing or reducing this chitin-to-chitosan conversion were not always consistent with it. Today, we believe that chitosans may play additional roles beyond that of an invisibility cloak, among them most prominently surface attachment to host cells. In the review, we have summarized this evidence for different roles of chitosans in fungal pathogenicity and virulence and tried to suggest promising future research approaches, such as the development of chitin deacetylase inhibitors as antifungal drugs.