Functional analysis ofHO gene in delayed homothallism inSaccharomyces cerevisiae wy2

Understanding the evolution of sex and recombination, key factors in the evolution of life, is a major challenge in biology. Studies of reproduction strategies of natural populations are important to complement the theoretical and experimental models. Fungi with both sexual and asexual life cycles are an interesting system for understanding the evolution of sex. In a study of natural populations of yeast Saccharomyces cerevisiae, we found that the isolates are heterothallic, meaning their mating type is stable, while the general belief is that natural S. cerevisiae strains are homothallic (can undergo mating-type switching). Mating-type switching is a gene-conversion process initiated by a site-specific endonuclease HO; this process can be followed by mother–daughter mating. Heterothallic yeast can mate with unrelated haploids (amphimixis), or undergo mating between spores from the same tetrad (intratetrad mating, or automixis), but cannot undergo mother–daughter mating as homothallic yeasts can. Sequence analysis of HO gene in a panel of natural S. cerevisiae isolates revealed multiple mutations. Good correspondence was found in the comparison of population structure characterized using 19 microsatellite markers spread over eight chromosomes and the HO sequence. Experiments that tested whether the mating-type switching pathway upstream and downstream of HO is functional, together with the detected HO mutations, strongly suggest that loss of function of HO is the cause of heterothallism. Furthermore, our results support the hypothesis that clonal reproduction and intratetrad mating may predominate in natural yeast populations, while mother–daughter mating might not be as significant as was considered.

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“…1995). In another study, the same mutation was found to reduce, but not abolish, the ability to switch mating type (Ekino et al. 1999).…”

Section: Resultsmentioning

confidence: 95%

Heterothallism inSaccharomyces cerevisiaeisolates from nature: effect ofHOlocus on the mode of reproduction

et al. 2010

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“…2). The predicted C. glabrata and K. delphensis Ho proteins have 68% sequence identity to each other and 57% identity to S. cerevisiae Ho protein and show conservation of the two LAGLIDADG endonuclease motifs and the Gly-223 residue identified as essential for mating-type switching in S. cerevisiae (16).…”

Section: Resultsmentioning

confidence: 98%

Evolution of the MAT locus and its Ho endonuclease in yeast species

Butler

Kenny

Fagan

et al. 2004

Proc. Natl. Acad. Sci. U.S.A.

220

225

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The genetics of the mating-type (MAT) locus have been studied extensively in Saccharomyces cerevisiae, but relatively little is known about how this complex system evolved. We compared the organization of MAT and mating-type-like (MTL) loci in nine species spanning the hemiascomycete phylogenetic tree. We inferred that the system evolved in a two-step process in which silent HMR͞HML cassettes appeared, followed by acquisition of the Ho endonuclease from a mobile genetic element. Ho-mediated switching between an active MAT locus and silent cassettes exists only in the Saccharomyces sensu stricto group and their closest relatives: Candida glabrata, Kluyveromyces delphensis, and Saccharomyces castellii. We identified C. glabrata MTL1 as the ortholog of the MAT locus of K. delphensis and show that switching between C. glabrata MTL1a and MTL1␣ genotypes occurs in vivo. The more distantly related species Kluyveromyces lactis has silent cassettes but switches mating type without the aid of Ho endonuclease. Very distantly related species such as Candida albicans and Yarrowia lipolytica do not have silent cassettes. In Pichia angusta, a homothallic species, we found MAT␣2, MAT␣1, and MATa1 genes adjacent to each other on the same chromosome. Although some continuity in the chromosomal location of the MAT locus can be traced throughout hemiascomycete evolution and even to Neurospora, the gene content of the locus has changed with the loss of an HMG domain gene (MATa2) from the MATa idiomorph shortly after HO was recruited.M ating in Saccharomyces cerevisiae is a choreographed fusion of two haploid cells with opposite mating types to form a diploid zygote. The mating type of a haploid cell is determined by its genotype at the mating-type (MAT) locus on chromosome III. The two variants of the MAT locus, MAT␣ and MATa, are referred to as idiomorphs rather than alleles because they differ in sequence, size, and gene content (1). Characterization of homothallic and heterothallic strains of S. cerevisiae by Winge and Lindegren (2) led to the discovery of genetic loci controlling homothallism and ultimately to the cassette model of mating-type switching proposed by Herskowitz and colleagues (3). The cassette model, which has been thoroughly verified by experimentation (4, 5), states that a haploid cell can switch genotype at the MAT locus (from MATa to MAT␣ or vice versa) by a gene-conversion process that involves replacing the genetic information at MAT with information copied from one of two silent cassette loci, HML␣ or HMRa. The gene conversion is initiated at a double-stranded DNA break made by the Ho endonuclease, encoded by the HO gene on chromosome IV, which cuts at a site that marks the boundary between the Y sequences unique to the MATa or MAT␣ idiomorphs and the shared Z sequence flanking them. HO is expressed only in cells that have budded once, which means that only mother cells switch mating type and neighboring cells in a colony can mate (4). Hence, most natural isolates of S. cerevisiae are diploid and phenotypic...

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“…The prototrophic yeast deletion collection strains described above were used for both mutant screens conducted as part of this study (MATa can1Δ::STE2pr-SpHIS5 lyp1 his3 ho − ). As a surrogate for wild-type behavior, the hoΔ::kanMX strain from the deletion collection was used, although all strains have nonfunctional HO alleles containing the standard amino acid replacements found in S288C-derived strains (T189A, G223S, L405S, H475L) (44,45). Data for the analysis of changes in gene expression as the result of mild heat shock (28-36°C) were acquired using a prototrophic, CEN.PK derivative (DBY11092 MATa MAL2-8 C ) as part of a previous study (9,46).…”

Section: Methodsmentioning

confidence: 99%

Yeast metabolic and signaling genes are required for heat-shock survival and have little overlap with the heat-induced genes

Gibney

Caudy

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

114

119

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Genome-wide gene-expression studies have shown that hundreds of yeast genes are induced or repressed transiently by changes in temperature; many are annotated to stress response on this basis. To obtain a genome-scale assessment of which genes are functionally important for innate and/or acquired thermotolerance, we combined the use of a barcoded pool of ∼4,800 nonessential, prototrophic Saccharomyces cerevisiae deletion strains with Illuminabased deep-sequencing technology. As reported in other recent studies that have used deletion mutants to study stress responses, we observed that gene deletions resulting in the highest thermosensitivity generally are not the same as those transcriptionally induced in response to heat stress. Functional analysis of identified genes revealed that metabolism, cellular signaling, and chromatin regulation play roles in regulating thermotolerance and in acquired thermotolerance. However, for most of the genes identified, the molecular mechanism behind this action remains unclear. In fact, a large fraction of identified genes are annotated as having unknown functions, further underscoring our incomplete understanding of the response to heat shock. We suggest that survival after heat shock depends on a small number of genes that function in assessing the metabolic health of the cell and/or regulate its growth in a changing environment.

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Functional analysis ofHO gene in delayed homothallism inSaccharomyces cerevisiae wy2

Cited by 14 publications

References 25 publications

Heterothallism inSaccharomyces cerevisiaeisolates from nature: effect ofHOlocus on the mode of reproduction

Heterothallism inSaccharomyces cerevisiaeisolates from nature: effect ofHOlocus on the mode of reproduction

Evolution of the MAT locus and its Ho endonuclease in yeast species

Yeast metabolic and signaling genes are required for heat-shock survival and have little overlap with the heat-induced genes

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