Completion of a parasexual cycle in Candida albicans by induced chromosome loss in tetraploid strains

Abstract

The human pathogenic fungus Candida albicans has traditionally been classi®ed as a diploid, asexual organism. However, mating-competent forms of the organism were recently described that produced tetraploid mating products. In principle, the C.albicans life cycle could be completed via a sexual process, via a parasexual mechanism, or by both mechanisms. Here we describe conditions in which growth of a tetraploid strain of C.albicans on Saccharomyces cerevisiaè pre-sporulation' medium induced ef®cient, random chromosome loss in the tetraploid. The products of chromosome loss were often strains that were diploid, or very close to diploid, in DNA content. If they inherited the appropiate MTL (mating-type like) loci, these diploid products were themselves mating competent. Thus, an ef®cient parasexual cycle can be performed in C.albicans, one that leads to the reassortment of genetic material in this organism. We show that this parasexual cycleÐconsisting of mating followed by chromosome lossÐcan be used in the laboratory for simple genetic manipulations in C.albicans.

Loss and gain of chromosome 5 controls growth of Candida albicans on sorbose due to dispersed redundant negative regulators

“…USA (102, 9541-9546; first published June 24, 2005; 10.1073͞ pnas.0501865102), the authors note the following: ''The stationary distribution of fixed genotypes (Eq. 9) was previously derived (1,2) in the context of the evolution of transcription factor binding sites, by using detailed balance of the substitution dynamics (Eq. 3).…”

Ploidy reduction in Saccharomyces cerevisiae

“…The same aneuploid chromosomes (a) ( b) were often maintained in transitions from tetraploidand triploid-sized to diploid-sized colonies (figure 2), which is further evidence for concerted chromosome loss. Concerted chromosome loss leading to ploidy reduction has also been inferred in the related yeast species, Candida albicans (Bennett & Johnson 2003). Polyploid genomes are known to be unstable in S. cerevisiae (Mayer & Aguilera 1990;Andalis et al 2004;Storchová et al 2006).…”

Stress-Induced Phenotypic Switching inCandida albicans

“…One copy of GAL1 was deleted in SN78 as described previously (Bennett and Johnson, 2003), and the URA3 gene was counterselected using 5-fluororotic acid (5-FOA). Subsequently, one copy of ADE2 was deleted using the method described previously (Hull et al, 2000), generating the URA3 ϩ strains RBY1038 and RBY1039, respectively.…”

“…To further analyze a potential relationship between growth rates and white-opaque switching, we tested progeny from the parasexual cycle of C. albicans for their doubling times and switching frequencies. Sexual reproduction in C. albicans occurs between opaque a and ␣ cells and is completed by an unusual mechanism of chromosome loss in tetraploid strains, generating recombinant diploid and aneuploid products (Bennett and Johnson, 2003;Forche et al, 2008). Previous studies demonstrated that many of the progeny derived from the parasexual cycle were slower growing than parental SC5314 strains, even in progeny with a euploid complement of chromosomes (Forche et al, 2008).…”