How does a hypha grow? The biophysics of pressurized growth in fungi

The underlying mechanisms for the growth of fungal hyphae are rooted in the physical property of cell pressure. The internal hydrostatic pressure (turgor) is one of the major forces that drives the localized expansion at the hyphal tip, which is the cause of the characteristic filamentous shape of the hypha. Calcium gradients regulate tip growth, secretory vesicles that contribute to this process are actively transported to the growing tip by molecular motors along cytoskeletal structures. Turgor is controlled by an osmotic MAP kinase cascade that causes de novo synthesis of osmolytes and ion uptake from the external medium. However, as discussed in this Review, turgor and pressure have additional roles in hyphal growth, for example, by causing the mass flow of cytoplasm from the basal mycelial network towards the expanding hyphal tips at the colony edge.