Differential Requirement for the Cell Wall Integrity Sensor Wsc1p in Diploids Versus Haploids.

Allison E Hall,Miriam Lisci,Mark D Rose

doi:10.3390/jof7121049

Abstract

The primary role of the Cell Wall Integrity Pathway (CWI) in Saccharomyces cerevisiae is monitoring the state of the cell wall in response to general life cycle stresses (growth and mating) and imposed stresses (temperature changes and chemicals). Of the five mechanosensor proteins monitoring cell wall stress, Wsc1p and Mid2p are the most important. We find that WSC1 has a stringent requirement in zygotes and diploids, unlike haploids, and differing from MID2’s role in shmoos. Diploids lacking WSC1 die frequently, independent of mating type. Death is due to loss of cell wall and plasma membrane integrity, which is suppressed by osmotic support. Overexpression of several CWI pathway components suppress wsc1∆ zygotic death, including WSC2, WSC3, and BEM2, as well as the Rho-GAPS, BEM3 and RGD2. Microscopic observations and suppression by BEM2 and BEM3 suggest that wsc1∆ zygotes die during bud emergence. Downstream in the CWI pathway, overexpression of a hyperactive protein kinase C (Pkc1p-R398P) causes growth arrest, and blocks the pheromone response. With moderate levels of Pkc1p-R398P, cells form zygotes and the wsc1∆ defect is suppressed. This work highlights functional differences in the requirement for Wsc1p in diploids Versus haploids and between Mid2p and Wsc1p during mating.

Highlights

During a screen for mating phenotypes caused by loss of function mutations of the cell wall integrity (CWI) pathway transmembrane proteins, we found that WSC1 has a zygote/diploid specific role
Wsc1p and Mid2p are thought to act as mechanosensors, detecting changes in the cell wall and transducing signals to activate the CWI pathway [34,35]
Cells exhibiting a mating defect do not form diploids efficiently when mated to fus1∆ fus2∆ strains [42]; we used this strain to initially determine if wsc1∆ cells showed a mating defect

Summary

Introduction

The budding yeast, Saccharomyces cerevisiae, is a single-celled organism that lives in a relatively harsh environment in the wild, undergoing stresses due to changes in osmotic pressure and temperature. To survive in this environment, yeast have evolved a robust cell wall that protects against rapid osmotic changes and mechanical stresses, while providing support for shape changes during budding and polarized growth in response to pheromone [1,2]. The CWI pathway is a signaling cascade that is regulated by five transmembrane sensor proteins that extend into the cell wall (Wsc1-3p, Mid2p, and Mtl1p) and regulate a series of MAP kinases [6,7,8,9] (Figure 1). The transmembrane proteins interact with Rom2p, a guanosine-nucleotide exchange factor (GEF) for Rho1p, a GTPase and master regulator of the CWI pathway [8]

Methods

Results

Conclusion