Paper accepted: “Chitin deacetylases are required for Epichloë festucae endophytic cell wall remodelling during establishment of a mutualistic symbiotic interaction with Lolium perenne”

Today, a paper by Nazanin Noorifar and her colleagues from the group of Prof. Barry Scott at Massey University in New Zealand was accepted for publication in the journal “Molecular Plant-Microbe Interactions”. In her manuscript, she describes the knock-out of the two active chitin deacetylase genes in the fungus Epichloë festucae growing as an endophyte in the leaves of the grass Lolium perenne. This fungus converts the chitin in its cell wall into chitosan during endophytic growth, just like as we described long ago for some biotrophic plant pathogenic fungi (El Gueddari et al. 2002) and suggested more recently also for an endophytic fungus (Cord-Landwehr et al. 2016), presumably to escape the host plant’s immune system. The Scott group investigated whether a knock-out of the chitin deacetylase genes (cda) would prevent this molecular stealth mechanism and lead to defense reactions in the plant during fungal colonisation. Tobias Weikert from our group was involved in this study because of our expertise in cytochemical visualization of chitin and chitosans (Nampally et al. 2012; Fuenzalida et al. 2014). The knock-out of either or both of the cda genes had severe effects on the morphology of endosymbiotic hyphae but surprisingly, only the single knock-out of cdaB influenced in planta growth of the fungus, which however was increased rather than decreased, and no chitin was detectable in the endosymbiotic hyphae. This is a bit reminiscent of a similar, even more comprehensive parallel study by the group of Prof. Regine Kahmann in Marburg for the plant pathogenic fungus Ustilago maydis in which we were equally involved (Rizzi et al. 2021), where knock-out of cda4 reduced chitin to chitosan conversion in the pathogenic hyphae but did not influence pathogenicity, while cda7 knock-out reduced virulence without changing cell wall chitosan. Clearly, in spite of these very detailed studies (and some other, less comprehensive ones recently published by other groups) which both took many years to complete, we still lack a real understanding of the role of chitin deacetylation during in planta fungal growth.