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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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Schematic Summary of Genomic Profiles of Progeny Diploid Strains Derived from the Δspo11 Tetraploid Strain via the Parasexual CycleProgeny strains were analyzed by SNP and CGH microarrays to determine the genetic content of each strain. As described in the legend to Figure 4, chromosome homologues are indicated by blue and pink bars to represent “maternal” and “paternal” homologues, respectively. In cases where a chromosome is trisomic, this is indicated by a bracket to the right of the chromosome. Ps1 to Ps8 progeny strains were derived from growth of the Δspo11 tetraploid (RBY176 or RBY177) on pre-spo medium, while Ss1 to Ss10 strains were derived from Δspo11 tetraploid growth on sorbose medium. Detailed SNP and CGH array data are provided in Tables S5 and S6 and Figure S4.
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pbio-0060110-g007: Schematic Summary of Genomic Profiles of Progeny Diploid Strains Derived from the Δspo11 Tetraploid Strain via the Parasexual CycleProgeny strains were analyzed by SNP and CGH microarrays to determine the genetic content of each strain. As described in the legend to Figure 4, chromosome homologues are indicated by blue and pink bars to represent “maternal” and “paternal” homologues, respectively. In cases where a chromosome is trisomic, this is indicated by a bracket to the right of the chromosome. Ps1 to Ps8 progeny strains were derived from growth of the Δspo11 tetraploid (RBY176 or RBY177) on pre-spo medium, while Ss1 to Ss10 strains were derived from Δspo11 tetraploid growth on sorbose medium. Detailed SNP and CGH array data are provided in Tables S5 and S6 and Figure S4.

Mentions: Genomic profiles of the Δspo11 diploid progeny (along with the parental diploid and tetraploid strains) were generated using SNP and CGH microarrays (see Figure 7, as well as Tables S5 and S6, and Figures S1 and S4). One of the diploid parents (RBY79, MTLα parent) was initially homozygous for Chr 2, and the other parent (RBY77, MTLa parent) carried a long tract of LOH on Chr 2 (Figure 7). This is reflected in the patterns of Chr 2 inheritance in the diploid progeny which either received only one type of Chr 2 homologue (Ps2, Ps3, Ps4, Ps5, Ps6, Ss1, Ss2, Ss3, Ss4, Ss8, and Ss10) or received two homologues that only differ near the Chr 2R telomere (Ps1, Ps7, Ps8, Ss5, Ss6, Ss7, and Ss9). Similarly, one of the gal1Δ Chr 1 homologues in the parental MTLa strain had undergone LOH of a single SNP near the telomere of Chr 1L and this LOH tract was retained in all of the progeny.


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)

Schematic Summary of Genomic Profiles of Progeny Diploid Strains Derived from the Δspo11 Tetraploid Strain via the Parasexual CycleProgeny strains were analyzed by SNP and CGH microarrays to determine the genetic content of each strain. As described in the legend to Figure 4, chromosome homologues are indicated by blue and pink bars to represent “maternal” and “paternal” homologues, respectively. In cases where a chromosome is trisomic, this is indicated by a bracket to the right of the chromosome. Ps1 to Ps8 progeny strains were derived from growth of the Δspo11 tetraploid (RBY176 or RBY177) on pre-spo medium, while Ss1 to Ss10 strains were derived from Δspo11 tetraploid growth on sorbose medium. Detailed SNP and CGH array data are provided in Tables S5 and S6 and Figure S4.
© Copyright Policy
Related In: Results  -  Collection

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

pbio-0060110-g007: Schematic Summary of Genomic Profiles of Progeny Diploid Strains Derived from the Δspo11 Tetraploid Strain via the Parasexual CycleProgeny strains were analyzed by SNP and CGH microarrays to determine the genetic content of each strain. As described in the legend to Figure 4, chromosome homologues are indicated by blue and pink bars to represent “maternal” and “paternal” homologues, respectively. In cases where a chromosome is trisomic, this is indicated by a bracket to the right of the chromosome. Ps1 to Ps8 progeny strains were derived from growth of the Δspo11 tetraploid (RBY176 or RBY177) on pre-spo medium, while Ss1 to Ss10 strains were derived from Δspo11 tetraploid growth on sorbose medium. Detailed SNP and CGH array data are provided in Tables S5 and S6 and Figure S4.
Mentions: Genomic profiles of the Δspo11 diploid progeny (along with the parental diploid and tetraploid strains) were generated using SNP and CGH microarrays (see Figure 7, as well as Tables S5 and S6, and Figures S1 and S4). One of the diploid parents (RBY79, MTLα parent) was initially homozygous for Chr 2, and the other parent (RBY77, MTLa parent) carried a long tract of LOH on Chr 2 (Figure 7). This is reflected in the patterns of Chr 2 inheritance in the diploid progeny which either received only one type of Chr 2 homologue (Ps2, Ps3, Ps4, Ps5, Ps6, Ss1, Ss2, Ss3, Ss4, Ss8, and Ss10) or received two homologues that only differ near the Chr 2R telomere (Ps1, Ps7, Ps8, Ss5, Ss6, Ss7, and Ss9). Similarly, one of the gal1Δ Chr 1 homologues in the parental MTLa strain had undergone LOH of a single SNP near the telomere of Chr 1L and this LOH tract was retained in all of the progeny.

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