Intracellular mechanisms of fungal space searching in microenvironments

Abstract

AbstractThe underlying intracellular mechanisms involved in the fungal growth received considerable attention, but the experimental and theoretical work did not take into account the modulation of these processes by constraining microenvironments similar to many natural fungal habitats. To fill this gap in the scientific knowledge, we used time-lapse live-cell imaging of Neurospora crassa growth in custom-built confining microfluidics environments. We show that the position and dynamics of the Spitzenkörper-microtubules system in constraining environments differs markedly from that associated with unconstrained growth. First, when hyphae encounter an obstacle at shallow angles, the Spitzenkörper moves from its central position in the apical dome off-axis towards a contact with the obstacle, thus functioning as a compass preserving the ‘directional memory’ of the initial growth. The trajectory of Spitzenkörper is also followed by microtubules, resulting in a ‘cutting corners’ pattern of the cytoskeleton in constrained geometries. Second, when an obstacle blocks a hypha at nearnormal incidence, the Spitzenkörper-microtubule system temporarily disintegrates, followed by the formation of two equivalent systems in the proto-hyphae – the basis of obstacle-induced branching. Third, a hypha, passing a lateral opening along a wall, continues to grow largely unperturbed while a lateral proto-hypha gradually branches into the opening, which starts forming its own Spitzenkörper-microtubule system. These observations suggest that the Spitzenkörper-microtubules system conserves the directional memory of the hyphae when they navigate around obstacles, but in the absence of the Spitzenkörper-microtubule system during constrainment-induced apical splitting and lateral branching, the probable driving force of obstacle-induced branching is the isotropic turgor pressure.