Instantaneous change in hyphal diameter in basidiomycete fungi

Abstract

Under certain conditions, fungi are capable to fast (down to seconds) change the size of their cells. For example, it is known that the cells of many species of yeasts under hyperosmotic conditions instantly and reversibly shrink entirely, without plasmolysis, with a decrease in volume of up to 40% or more. There is limited data that filamentous fungi can also instantly change the diameter of their unspecialized hyphae. This property is fundamental and is a powerful tool for survival and preservation of the physiological functionality of the fungus in sharply changing external conditions, but requires detailed study. In this work, which is a large-scale (more than 50,000 cells measured) light microscopic study, the ability of three unrelated basidiomycete species to fast change the diameter of their hyphae under the influence of various factors was analyzed. It was found, for example, that all three fungi respond similarly to moderate hyperosmotic shock and shrink by an average of 12-14% in diameter, but inhibitors of actin assembly can cause both expansion and shrinkage of hyphae, or have no effect on a fungus. Combining the current results with those previously obtained in the study of macroinvagination systems of the fungal plasma membrane, different approaches for basidiomycetes to respond to sudden stress changes were proposed. The curtain model was also expanded, describing a common rapid response mechanism. The mechanism includes elastic properties of the cell wall, adhesion of the plasma membrane to it, regulation of turgor, the actin cables system that regulate the tension of the plasma membrane and cell size, and the complex system of macroinvaginations of the plasma membrane, ensuring the constant integrity and functionality of the latter.