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The parasexual cycle in Candida albicans provides an alternative pathway to meiosis for the formation of recombinant strains.

Forche A, Alby K, Schaefer D, Johnson AD, Berman J, Bennett RJ - PLoS Biol. (2008)

Bottom Line: We show that deletion of SPO11 prevented genetic recombination between homologous chromosomes during the C. albicans parasexual cycle.These findings suggest that at least one meiosis-specific gene has been re-programmed to mediate genetic recombination during the alternative parasexual life cycle of C. albicans.We discuss, in light of the long association of C. albicans with warm-blooded animals, the potential advantages of a parasexual cycle over a conventional sexual cycle.

View Article: PubMed Central - PubMed

Affiliation: Department of Genetics, Cell Biology and Development, University of Minnesota, Minneapolis, Minnesota, United States of America.

ABSTRACT
Candida albicans has an elaborate, yet efficient, mating system that promotes conjugation between diploid a and alpha strains. The product of mating is a tetraploid a/alpha cell that must undergo a reductional division to return to the diploid state. Despite the presence of several "meiosis-specific" genes in the C. albicans genome, a meiotic program has not been observed. Instead, tetraploid products of mating can be induced to undergo efficient, random chromosome loss, often producing strains that are diploid, or close to diploid, in ploidy. Using SNP and comparative genome hybridization arrays we have now analyzed the genotypes of products from the C. albicans parasexual cycle. We show that the parasexual cycle generates progeny strains with shuffled combinations of the eight C. albicans chromosomes. In addition, several isolates had undergone extensive genetic recombination between homologous chromosomes, including multiple gene conversion events. Progeny strains exhibited altered colony morphologies on laboratory media, demonstrating that the parasexual cycle generates phenotypic variants of C. albicans. In several fungi, including Saccharomyces cerevisiae and Schizosaccharomyces pombe, the conserved Spo11 protein is integral to meiotic recombination, where it is required for the formation of DNA double-strand breaks. We show that deletion of SPO11 prevented genetic recombination between homologous chromosomes during the C. albicans parasexual cycle. These findings suggest that at least one meiosis-specific gene has been re-programmed to mediate genetic recombination during the alternative parasexual life cycle of C. albicans. We discuss, in light of the long association of C. albicans with warm-blooded animals, the potential advantages of a parasexual cycle over a conventional sexual cycle.

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Morphology of Diploid Progeny Strains Derived from the Δspo11 Tetraploid StrainProgeny strains were grown on YPD medium at 30 °C for 7 d and colonies photographed. Progeny strains Ps1 to Ps8 were derived from growth of the Δspo11 tetraploid strain on pre-spo medium, while strains Ss1 to Ss10 were derived from growth on sorbose medium. A control diploid strain (SC5314) and tetraploid strain (RBY176) are shown for comparison.
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pbio-0060110-g006: Morphology of Diploid Progeny Strains Derived from the Δspo11 Tetraploid StrainProgeny strains were grown on YPD medium at 30 °C for 7 d and colonies photographed. Progeny strains Ps1 to Ps8 were derived from growth of the Δspo11 tetraploid strain on pre-spo medium, while strains Ss1 to Ss10 were derived from growth on sorbose medium. A control diploid strain (SC5314) and tetraploid strain (RBY176) are shown for comparison.

Mentions: The observation that C. albicans Spo11p is expressed during mitotic growth is consistent with it having a function outside of meiosis. To examine if C. albicans Spo11p is required for genetic recombination in the parasexual mating cycle, we deleted all four copies of the SPO11 gene in genetically marked tetraploid strains (RBY176/RBY177) that were heterozygous for GAL1 on Chr 1. The strains were induced to undergo concerted chromosome loss on pre-spo or sorbose medium and were then exposed to 2-DOG to select for strains that had lost both copies of GAL1. Eighteen DOGR colonies were selected from tetraploid growth on pre-spo (eight colonies) or sorbose (ten colonies) and subsequently analyzed by flow cytometry to determine if they were diploid, or near diploid, strains (Figure S2). Indeed, we detected diploid Δspo11 progeny strains, indicating that Spo11p is not necessary for the process of concerted chromosome loss in tetraploid C. albicans strains. We next analyzed the colony morphologies of the Δspo11 diploid progeny. As was seen with progeny from wild-type tetraploids (Figure 4), many of the Δspo11 progeny strains exhibited altered colony morphologies on YPD medium (Figure 6).


The parasexual cycle in Candida albicans provides an alternative pathway to meiosis for the formation of recombinant strains.

Forche A, Alby K, Schaefer D, Johnson AD, Berman J, Bennett RJ - PLoS Biol. (2008)

Morphology of Diploid Progeny Strains Derived from the Δspo11 Tetraploid StrainProgeny strains were grown on YPD medium at 30 °C for 7 d and colonies photographed. Progeny strains Ps1 to Ps8 were derived from growth of the Δspo11 tetraploid strain on pre-spo medium, while strains Ss1 to Ss10 were derived from growth on sorbose medium. A control diploid strain (SC5314) and tetraploid strain (RBY176) are shown for comparison.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2365976&req=5

pbio-0060110-g006: Morphology of Diploid Progeny Strains Derived from the Δspo11 Tetraploid StrainProgeny strains were grown on YPD medium at 30 °C for 7 d and colonies photographed. Progeny strains Ps1 to Ps8 were derived from growth of the Δspo11 tetraploid strain on pre-spo medium, while strains Ss1 to Ss10 were derived from growth on sorbose medium. A control diploid strain (SC5314) and tetraploid strain (RBY176) are shown for comparison.
Mentions: The observation that C. albicans Spo11p is expressed during mitotic growth is consistent with it having a function outside of meiosis. To examine if C. albicans Spo11p is required for genetic recombination in the parasexual mating cycle, we deleted all four copies of the SPO11 gene in genetically marked tetraploid strains (RBY176/RBY177) that were heterozygous for GAL1 on Chr 1. The strains were induced to undergo concerted chromosome loss on pre-spo or sorbose medium and were then exposed to 2-DOG to select for strains that had lost both copies of GAL1. Eighteen DOGR colonies were selected from tetraploid growth on pre-spo (eight colonies) or sorbose (ten colonies) and subsequently analyzed by flow cytometry to determine if they were diploid, or near diploid, strains (Figure S2). Indeed, we detected diploid Δspo11 progeny strains, indicating that Spo11p is not necessary for the process of concerted chromosome loss in tetraploid C. albicans strains. We next analyzed the colony morphologies of the Δspo11 diploid progeny. As was seen with progeny from wild-type tetraploids (Figure 4), many of the Δspo11 progeny strains exhibited altered colony morphologies on YPD medium (Figure 6).

Bottom Line: We show that deletion of SPO11 prevented genetic recombination between homologous chromosomes during the C. albicans parasexual cycle.These findings suggest that at least one meiosis-specific gene has been re-programmed to mediate genetic recombination during the alternative parasexual life cycle of C. albicans.We discuss, in light of the long association of C. albicans with warm-blooded animals, the potential advantages of a parasexual cycle over a conventional sexual cycle.

View Article: PubMed Central - PubMed

Affiliation: Department of Genetics, Cell Biology and Development, University of Minnesota, Minneapolis, Minnesota, United States of America.

ABSTRACT
Candida albicans has an elaborate, yet efficient, mating system that promotes conjugation between diploid a and alpha strains. The product of mating is a tetraploid a/alpha cell that must undergo a reductional division to return to the diploid state. Despite the presence of several "meiosis-specific" genes in the C. albicans genome, a meiotic program has not been observed. Instead, tetraploid products of mating can be induced to undergo efficient, random chromosome loss, often producing strains that are diploid, or close to diploid, in ploidy. Using SNP and comparative genome hybridization arrays we have now analyzed the genotypes of products from the C. albicans parasexual cycle. We show that the parasexual cycle generates progeny strains with shuffled combinations of the eight C. albicans chromosomes. In addition, several isolates had undergone extensive genetic recombination between homologous chromosomes, including multiple gene conversion events. Progeny strains exhibited altered colony morphologies on laboratory media, demonstrating that the parasexual cycle generates phenotypic variants of C. albicans. In several fungi, including Saccharomyces cerevisiae and Schizosaccharomyces pombe, the conserved Spo11 protein is integral to meiotic recombination, where it is required for the formation of DNA double-strand breaks. We show that deletion of SPO11 prevented genetic recombination between homologous chromosomes during the C. albicans parasexual cycle. These findings suggest that at least one meiosis-specific gene has been re-programmed to mediate genetic recombination during the alternative parasexual life cycle of C. albicans. We discuss, in light of the long association of C. albicans with warm-blooded animals, the potential advantages of a parasexual cycle over a conventional sexual cycle.

Show MeSH
Related in: MedlinePlus