The Woronin Body: A Fungal Organelle Regulating Multicellularity

In filamentous fungal species belonging to the Phyla Ascomycota and Basidiomycota, hyphae are compartmentalized into distinct cells by the formation of a septum. However, the septum does not completely separate hyphae due to the presence of a septal pore, which is a perforated structure that allows the exchange of the cytoplasmic constituents between adjacent hyphal cells. Cell-to-cell connectivity through the septal pore is associated with the catastrophic risk of cytoplasmic loss by cells adjacent to individually damaged hyphae. Pezizomycotina (filamentous Ascomycota) species have evolved to possess a specialized organelle called the Woronin body around the septum. The primary function of Woronin bodies is the prevention of excessive cytoplasmic loss from cells adjacent to damaged or lysed cells. Hex1, a major structural protein of Woronin bodies, is conserved in Pezizomycotina species. Woronin bodies differentiate from the peroxisomes and are typically tethered to the septum. Recent studies have identified additional septum-related components such as proteins containing intrinsically disordered regions and those involved in hyphal fusion/sexual reproduction and mitosis, which further elucidates molecular machineries governing the septal pore closure besides Woronin bodies.