No abstract

Background Information. Two main systems regulate plasma membrane tension (PMT) and provide a close connection between the protoplast and the cell wall in fungi: turgor pressure and the actin cytoskeleton. These systems work together with the plasma membrane focal adhesion to the cell wall and their contribution to fungal cell organization and physiology has been partially studied. However, it remains controversial in model filamentous ascomycetes and oomycetes and even less investigated in filamentous basidiomycetes. Early endocytosis can be used to research the mechanisms regulating PMT since the dynamics of early endocytosis is largely dependent on this tension. Results. This study examined the effects of actin polymerization inhibitors and hyperosmotic shock on early endocytosis and cell morphology in two filamentous basidiomycetes. The main obtained results are: (i) the depolymerisation of F-actin leads to the fast formation of endocytic pits while inhibiting of their scission from the plasma membrane and (ii) the moderate hyperosmotic shock does not affect the dynamics of early endocytosis. These and our other results have allowed suggesting a curtain model for the regulation of PMT in basidiomycetes. Conclusions and significance. According to the proposed curtain model, the PMT in many non-apical cells of hyphae is more often regulated not by turgor pressure but by a system of actin driver cables that are associated with the proteins of the focal adhesion sites. The change in PMT occurs similar to the movement of a curtain along the curtain rod using the curtain drivers. This model addresses the fundamental properties of the fungal structure and physiology. It requires confirmation including the currently technically unavailable high-quality labelling of the actin cytoskeleton of the basidiomycetes.

Two main systems regulate the plasmalemma tension and provide a close connection of the protoplast with the cell wall in fungi: turgor pressure and actin cytoskeleton. These systems work together with the plasmalemma focal adhesion to the cell wall and their contribution to fungal cell organization has been partially studied, but remains controversial in model filamentous ascomycetes and oomycetes, and even less investigated in filamentous basidiomycetes. Early endocytosis, in which F-actin is actively involved, can be used to research of mechanisms regulating the plasmalemma tension, since the latter influences on the primary endocytic vesicles formation. This study examined the effects of actin polymerization inhibitors and hyperosmotic shock on early endocytosis and cell morphology in two filamentous basidiomycetes. The main obtained results: (i) depolymerization of F-actin leads to the fast formation of primary endocytic vesicles but to inhibition of their scission; (ii) moderate hyperosmotic shock does not affect the dynamics of early endocytosis. These and a number of other results allowed offering a curtain model of regulation the plasmalemma tension in basidiomycetes. According to this model, the plasmalemma tension in many nonapical cells of hyphae is more often regulated not by turgor pressure, but by a system of actin driver cables that are associated with the proteins of focal adhesion sites. The change in the plasmalemma tension occurs similar to the movement of the curtain along the curtain rod using the curtain drivers. This model addresses the fundamental properties of the fungal structure and physiology and requires confirmation, including through the yet technically unavailable high quality labeling of the actin cytoskeleton of basidiomycetes.