LAM Genes Contribute to Environmental Stress Tolerance but Sensibilize Yeast Cells to Azoles.

Svyatoslav S Sokolov,Margarita A Vorobeva,Ekaterina A Smirnova,Nataliya I Trushina,Kseniia V Galkina,Fedor F Severin,Dmitry A Knorre,Alexandra I Smirnova

doi:10.3389/fmicb.2020.00038

Svyatoslav S Sokolov, Margarita A Vorobeva + Show 6 more

Open Access

https://doi.org/10.3389/fmicb.2020.00038

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Abstract

Lam proteins transport sterols between the membranes of different cellular compartments. In Saccharomyces cerevisiae, the LAM gene family consists of three pairs of paralogs. Because the function of paralogous genes can be redundant, the phenotypes of only a small number of LAM gene deletions have been reported; thus, the role of these genes in yeast physiology is still unclear. Here, we surveyed the phenotypes of double and quadruple deletants of paralogous LAM2(YSP2)/LAM4 and LAM1(YSP1)/LAM3(SIP3) genes that encode proteins localized in the junctions of the plasma membrane and endoplasmic reticulum. The quadruple deletant showed increased sterol content and a strong decrease in ethanol, heat shock and high osmolarity resistance. Surprisingly, the quadruple deletant and LAM2/LAM4 double deletion strain showed increased tolerance to the azole antifungals clotrimazole and miconazole. This effect was not associated with an increased rate of ABC-transporter substrate efflux. Possibly, increased sterol pool in the LAM deletion strains postpones the effect of azoles on cell growth. Alternatively, LAM deletions might alleviate the toxic effect of sterols as Lam proteins can transport toxic sterol biosynthesis intermediates into membrane compartments that are sensitive to these compounds. Our findings reveal novel biological roles of LAM genes in stress tolerance and suggest that mutations in these genes may confer upregulation of a mechanism that provides resistance to azole antifungals in pathogenic fungi.

Highlights

Ergosterol is a primary sterol found in the plasma membrane of Ascomycota fungi (Weete et al, 2010)
While cells can proliferate without the genes ERG2, ERG3, ERG4, ERG5, and ERG6, which are required for the later steps of the ergosterol biosynthesis pathway (Giaever et al, 2002), deletions of these genes have been shown to decrease yeast fitness under non-optimal conditions (Abe and Hiraki, 2009; Jakubkova et al, 2016; Liu et al, 2017)
We found that the cells of the quadruple deletant, Δlam1Δlam2Δlam3Δlam4, have increased sterol content and decreased resistance to some environmental stresses, such as heat shock, increased salinity, and high ethanol concentrations

Summary

Introduction

Ergosterol is a primary sterol found in the plasma membrane of Ascomycota fungi (Weete et al, 2010). LAM Genes Deletions Phenotypes the deletion of ERG genes increases the resistance of yeast cells to some stresses, including high osmolarity (Bard et al, 1978) and high tetramethylammonium concentrations (Kodedová and Sychrová, 2015). These effects are linked to hyperpolarization of the plasma membrane in ergosterol-deficient strains (Bard et al, 1978; Welihinda et al, 1994). While being essential for survival in some stressful conditions, high ergosterol content in the plasma membrane can be detrimental in other conditions

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