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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 Progeny Strains from the Parasexual Mating CycleProgeny strains derived from the tetraploid RBY18 strain by growth on pre-spo medium (P1 to P7) or sorbose medium (S1 to S6) were analyzed on YPD medium. Strains were grown at 30 °C for 7 d and photographed. Many strains exhibited a mutant morphology, including increased surface wrinkling of the colonies indicative of increased hyphal cell formation. A control diploid strain (SC5314) and tetraploid strain (RBY18) are included for comparison.
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pbio-0060110-g003: Morphology of Progeny Strains from the Parasexual Mating CycleProgeny strains derived from the tetraploid RBY18 strain by growth on pre-spo medium (P1 to P7) or sorbose medium (S1 to S6) were analyzed on YPD medium. Strains were grown at 30 °C for 7 d and photographed. Many strains exhibited a mutant morphology, including increased surface wrinkling of the colonies indicative of increased hyphal cell formation. A control diploid strain (SC5314) and tetraploid strain (RBY18) are included for comparison.

Mentions: To further characterize the strains generated by parasexual chromosome reduction, progeny were plated for single colonies on rich (YPD) medium to examine colony growth. After incubation at 30 °C for 7 d, colonies were compared for overall size and morphology (Figure 3). A wide range of phenotypes was observed, including smaller colony sizes relative to diploid and tetraploid parental strains and altered colony morphologies. Some of the isolates produced hyper-filamentous morphologies, as evidenced by increased surface wrinkling of the colonies (e.g., progeny strains P3, P4, and P6; Figure 3, panels E, F, and H). Normally, C. albicans cells grow as budding yeast, pseudohyphal, or true hyphal cells. Examination of cells from the wrinkled colonies by microscopy confirmed that these colonies contained many filamentous (pseudohyphal and true hyphal) cells, while the unwrinkled colonies (including control strains) contained very few filamentous cells (unpublished data). Some progeny strains also exhibited reduced filamentation on medium that normally induces hyphae formation (Spider medium and serum-containing medium, KA and RJB, unpublished data).


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 Progeny Strains from the Parasexual Mating CycleProgeny strains derived from the tetraploid RBY18 strain by growth on pre-spo medium (P1 to P7) or sorbose medium (S1 to S6) were analyzed on YPD medium. Strains were grown at 30 °C for 7 d and photographed. Many strains exhibited a mutant morphology, including increased surface wrinkling of the colonies indicative of increased hyphal cell formation. A control diploid strain (SC5314) and tetraploid strain (RBY18) are included for comparison.
© Copyright Policy
Related In: Results  -  Collection

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

pbio-0060110-g003: Morphology of Progeny Strains from the Parasexual Mating CycleProgeny strains derived from the tetraploid RBY18 strain by growth on pre-spo medium (P1 to P7) or sorbose medium (S1 to S6) were analyzed on YPD medium. Strains were grown at 30 °C for 7 d and photographed. Many strains exhibited a mutant morphology, including increased surface wrinkling of the colonies indicative of increased hyphal cell formation. A control diploid strain (SC5314) and tetraploid strain (RBY18) are included for comparison.
Mentions: To further characterize the strains generated by parasexual chromosome reduction, progeny were plated for single colonies on rich (YPD) medium to examine colony growth. After incubation at 30 °C for 7 d, colonies were compared for overall size and morphology (Figure 3). A wide range of phenotypes was observed, including smaller colony sizes relative to diploid and tetraploid parental strains and altered colony morphologies. Some of the isolates produced hyper-filamentous morphologies, as evidenced by increased surface wrinkling of the colonies (e.g., progeny strains P3, P4, and P6; Figure 3, panels E, F, and H). Normally, C. albicans cells grow as budding yeast, pseudohyphal, or true hyphal cells. Examination of cells from the wrinkled colonies by microscopy confirmed that these colonies contained many filamentous (pseudohyphal and true hyphal) cells, while the unwrinkled colonies (including control strains) contained very few filamentous cells (unpublished data). Some progeny strains also exhibited reduced filamentation on medium that normally induces hyphae formation (Spider medium and serum-containing medium, KA and RJB, unpublished data).

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