Structural and regulatory dynamics of septum development in fungal hyphae

Filamentous fungi grow through hyphae, divided by septa with central pores that allow cytoplasmic flow, supporting coenocytic behavior. Septa provide structural rigidity, contain damage by plugging pores during injury, and aid in developmental processes like conidiation. Septum formation is tightly regulated, involving selection of the septation site, actomyosin ring assembly and cell wall deposition. Recent advances in microscopy and molecular studies have clarified many aspects of septation, however some mechanisms remain unclear. This review examines the roles, structure, and regulation of hyphal septa, emphasizing their dynamic functions in structural support, damage control, and differentiation. Septa are multilayered structures composed of chitin and β-1,3-glucan, with Woronin bodies (WB) acting as emergency plugs in ascomycetes. The actin cytoskeleton, septins, and microtubule-organizing centers (MTOCs) are crucial for septum formation, with actin and associated proteins driving the contractile actomyosin ring (CAR). Septins organize into higher-order structures, regulating septation and fungal development. Regulatory networks, including the septation initiation network (SIN), coordinate mitosis and septation, with Rho GTPases playing key role. Despite progress, questions remain about protein transport, septum regulation, and evolutionary adaptations. This review highlights the complexity of septation and the need for further research to fully understand this essential process in filamentous fungi.