CsmA, a Class V Chitin Synthase with a Myosin Motor-like Domain, Is Localized through Direct Interaction with the Actin Cytoskeleton inAspergillus nidulans

Abstract

One of the essential features of fungal morphogenesis is the polarized synthesis of cell wall components such as chitin. The actin cytoskeleton provides the structural basis for cell polarity in Aspergillus nidulans, as well as in most other eukaryotes. A class V chitin synthase, CsmA, which contains a myosin motor-like domain (MMD), is conserved among most filamentous fungi. The DeltacsmA null mutant showed remarkable abnormalities with respect to cell wall integrity and the establishment of polarity. In this study, we demonstrated that CsmA tagged with 9x HA epitopes localized near actin structures at the hyphal tips and septation sites and that its MMD was able to bind to actin. Characterization of mutants bearing a point mutation or deletion in the MMD suggests that the interaction between the MMD and actin is not only necessary for the proper localization of CsmA, but also for CsmA function. Thus, the finding of a direct interaction between the chitin synthase and the actin cytoskeleton provides new insight into the mechanisms of polarized cell wall synthesis and fungal morphogenesis.