Loss and fragmentation of chromosome 5 are major events linked to the adaptation of rad52-DeltaDelta strains of Candida albicans to sorbose

Abstract

Candida albicans can adapt and grow on sorbose plates by losing one copy of Chr5. Since rad52 mutants of Saccharomyces cerevisiae lose chromosomes at a high rate, we have investigated the ability of C. albicans rad52 to adapt to sorbose. Carad52-DeltaDelta mutants generate Sou(+) strains earlier than wild-type but the final yield is lower, probably because they die at a higher rate in sorbose. As other strains of C. albicans, CAF2 and rad52-DeltaDelta derivatives generate Sou(+) strains by a loss of one copy of Chr5 about 75% of the time. In addition, rad52 strains were able to produce Sou(+) strains by a fragmentation/deletion event in one copy of Chr5, consisting of loss of a region adjacent to the right telomere. Finally, both CAF2 and rad52-DeltaDelta produced Sou(+) strains with two apparent full copies of Chr5, suggesting that additional genomic changes may also regulate adaptation to sorbose.

Fig. 1

(A) Viability of strains on sorbose plates. About 800 cells of each strain were plated in this experiment. For details see Materials and Methods. (B) Plates corresponding to an experiment similar to that indicated in Table 1 after 20 days of incubation on sorbose plates.

Fig. 2. MTL analysis and karyotyping of Sou⁺ strains with chromosomal rearrangements

A. PCR analysis of the MTL locus in representative Sou⁺ strains derived from CAF2 and rad52-ΔΔ. Lanes correspond to parental CAF2 Sou^- (lane 1); its Sou⁺ derivatives C-Sou⁺1 to C-Sou⁺3 (lane 2 to 4, respectively); parental rad52-ΔΔ Sou^- (lane 5); and its derivatives r-Sou⁺1 to r-Sou⁺6 (lane 6 to 11 respectively); B and C. Analysis of the standard electrophoretic karyotypes (left) (Ba) or the electrokaryotypes under conditions that separate homologues of the shortest chromosomes (panel Ca) of the strains indicated in A, and corresponding Southern blots (right) using the indicated probes. Arrows indicate obvious extrachromosomal bands. Bottom: Diagram of chromosome 5, showing the approximated location of the several markers or probes used in this study. The centromere is indicated (Sanyal et al., 2004).

Fig. 3. Analysis of copy number and heterozygosities of chromosome 4 in selected Sou⁺ strains

A) RBT7 analysis of the indicated strains. The control used is a homozygous strain for RBT7 isolated in our laboratory. B) Southern blot analysis of the RAD17 locus. Karyotypes are the same of Fig. 2Ba. Lanes are as in Fig. 2.

Fig. 4. Karyotypes of selected Sou⁺ MTL a/α strains lacking obvious chromosomal alterations

A) Standard electrophoretical karyotypes of new a/α Sou⁺ strains derived from CAF2 (C-Sou⁺4-6, lanes 1-3) or rad52-ΔΔ (r-Sou⁺7-12. lanes 4-9). B and C. Southern blot analysis of the karyotypes with the indicated probes of Chr5 (B) or Chr1 (C).