Molecular mechanisms of chemotropism and cell fusion in unicellular fungi.

Sophie G Martin

doi:10.1242/jcs.230706

Abstract

In all eukaryotic phyla, cell fusion is important for many aspects of life, from sexual reproduction to tissue formation. Fungal cells fuse during mating to form the zygote, and during vegetative growth to connect mycelia. Prior to fusion, cells first detect gradients of pheromonal chemoattractants that are released by their partner and polarize growth in their direction. Upon pairing, cells digest their cell wall at the site of contact and merge their plasma membrane. In this Review, I discuss recent work on the chemotropic response of the yeast models Saccharomyces cerevisiae and Schizosaccharomyces pombe, which has led to a novel model of gradient sensing: the cell builds a motile cortical polarized patch, which acts as site of communication where pheromones are released and sensed. Initial patch dynamics serve to correct its position and align it with the gradient from the partner cell. Furthermore, I highlight the transition from cell wall expansion during growth to cell wall digestion, which is imposed by physical and signaling changes owing to hyperpolarization that is induced by cell proximity. To conclude, I discuss mechanisms of membrane fusion, whose characterization remains a major challenge for the future.

Highlights

All cells – whether they live on their own or are part of a multicellular organism – interact with their environment
Uniform 1 nM pheromone concentration leads to unstable polarization in S. cerevisiae, which is very similar to the assembly-disassembly mode of S. pombe (Muller et al, 2016); in addition, S. pombe cells that lack one of three Cdc42 GTPase-activating proteins (GAP) displayed notable instances of local biased random walk (Gallo Castro and Martin, 2018)
One model is that phosphorylation of Gβ weakens its interaction with the Cdc42 guanine nucleotide exchange factor (GEF), allowing for more frequent probing of activated receptors, to update on local pheromone concentration information and prevent polarity site drift from active receptors (Deflorio et al, 2013) (Fig. 3)

Summary

Introduction

All cells – whether they live on their own or are part of a multicellular organism – interact with their environment. Stimulation by pheromones released at a closely positioned partner cell patch promotes stabilization for chemotropic growth.

Results

Conclusion