Histone chaperones and the Rrm3p helicase regulate flocculation in S. cerevisiae

Abstract

AbstractBackgroundBiofilm formation or flocculation is a major phenotype in wild type budding yeasts but rarely seen in laboratory yeast strains. Here, we analysed flocculation phenotypes and the expression ofFLOgenes in laboratory strains with various genetic backgrounds.ResultsWe show that mutations in histone chaperones, the helicaseRRM3and the Histone DeacetylaseHDA1de-repress theFLOgenes and partially reconstitute flocculation. We demonstrate that the loss of repression correlates to elevated expression of severalFLOgenes, to increased acetylation of histones at the promoter ofFLO1and to variegated expression ofFLO11. We show that these effects are related to the activity of CAF-1 at the replication forks. We also demonstrate that nitrogen starvation or inhibition of histone deacetylases do not produce flocculation inW303andBY4742strains but do so in strains compromised for chromatin maintenance. Finally, we correlate the de-repression ofFLOgenes to the loss of silencing at the subtelomeric and mating type gene loci.ConclusionsWe conclude that the deregulation of chromatin maintenance and transmission is sufficient to reconstitute flocculation in laboratory yeast strains. Consequently, we propose that a gain in epigenetic silencing is a major contributing factor for the loss of flocculation phenotypes in these strains. We suggest that flocculation in yeasts provides an excellent model for addressing the challenging issue of how epigenetic mechanisms contribute to evolution.