GH16 and GH81 family β-(1,3)-glucanases in Aspergillus fumigatus are essential for conidial cell wall morphogenesis

The fungal cell wall is a rigid structure because of fibrillar and branched -(1,3)-glucan linked to chitin. Softening of the cell wall is an essential phenomenon during fungal morphogenesis, wherein rigid cell wall structures are cleaved by glycosylhydrolases. During the search for glycosylhydrolases acting on -(1,3)-glucan, we identified seven genes in the Aspergillus fumigatus genome coding for potential endo--(1,3)-glucanase. ENG1 (previously characterized and named ENGL1, Mouyna et al.,), belongs to the Glycoside-Hydrolase 81 (GH81) family, while ENG2 to ENG7, to GH16 family. ENG1 and four GH16 genes (ENG2-5) were expressed in the resting conidia as well as during germination, suggesting an essential role during A. fumigatus morphogenesis. Here, we report the effect of sequential deletion of AfENG2-5 (GH16) followed by AfENG1 (GH81) deletion in the eng2,3,4,5 mutant. The eng1,2,3,4,5 mutant showed conidial defects, with linear chains of conidia unable to separate while the germination rate was not affected. These results show, for the first time in a filamentous fungus, that endo -(1,3)-glucanases are essential for proper conidial cell wall assembly and thus segregation of conidia during conidiation.