Hyphae in Hypha: Large-Scale Tubular and Tubular-Lamellar Endomembrane Fungal Systems

Filamentous fungi and oomycetes have four large intracellular membrane systems consisting of tubes, lamellae, or a combination thereof. Such elongated membrane structures can extend for tens of micrometers in hyphal cells, branching and connecting into bundles and networks. These systems are represented by tubular vacuoles, elongated mitochondria, endoplasmic reticulum, and macroinvaginations of the plasma membrane. They are most developed in xylotrophic and mycorrhiza-forming basidiomycetes. This review examines three membrane systems, excluding the macroinvagination system. It proposes that, at least in apical hyphae, tubular vacuoles, elongated mitochondria, and the endoplasmic reticulum form a single intrahyphal complex with shared physiological functions. The complex's primary function is the transport of solutes, independent of intrahyphal mass flow. In basidiomycetes, this transport independence from turgor gradients and changes not only provides energy and resources for rapid apical growth but also facilitates the exchange of resources with the host plant or the efficient concentration of nutrients from the woody substrate.