A novel Pezizomycotina-specific protein with gelsolin domains regulates contractile actin ring assembly and constriction in perforated septum formation

Septum formation in fungi is equivalent to cytokinesis. It differs mechanistically in filamentous ascomycetes (Pezizomycotina) from that of ascomycete yeasts by the retention of a central septal pore in the former group. However, septum formation in both groups is accomplished by contractile actin ring (CAR) assembly and constriction. The specific components regulating septal pore organization during septum formation are poorly understood. In this study, a novel Pezizomycotina-specific actin regulatory protein GlpA containing gelsolin domains was identified using bioinformatics. A glpA deletion mutant exhibited increased distances between septa, abnormal septum morphology and defective regulation of septal pore closure. In glpA deletion mutant hyphae, overaccumulation of actin filament (F-actin) was observed, and the CAR was abnormal with improper assembly and failure in constriction. In wild-type cells, GlpA was found at the septum formation site similarly to the CAR. The N-terminal 329 residues of GlpA are required for its localization to the septum formation site and essential for proper septum formation, while its C-terminal gelsolin domains are required for the regular CAR dynamics during septum formation. Finally, in this study we elucidated a novel Pezizomycotina-specific actin modulating component, which participates in septum formation by regulating the CAR dynamics.