Fine-resolution physical mapping of genomic diversity in Candida albicans

It has been suggested that Candida albicans, a diploid asexual fungus, achieves genetic diversity by genomic rearrangement. This important human pathogen may provide a system in which to analyze alternate routes to genomic diversity. C. albicans has a highly variable karyotype; its chromosomes contain a middle repeated DNA sequence called the Major Repeat Sequence (MRS), composed of subrepeats HOK, RPS, and RB2. RPS is tandemly repeated while the other subrepeats occur once in each MRS. Chromosome 7, the smallest of the eight chromosomes, has been previously mapped. The complete physical map of this chromosome was used to analyze chromosome 7 diversity in six strains, including two well-characterized laboratory strains (1006 and WO-1) and four clinical ones. We found four types of events to explain the genomic diversity: I) Chromosome length polymorphism (CLP) results from expansion and contraction of the RPS; 2) reciprocal translocation occurs at the MRS loci; 3) chromosomal deletion; and (4) trisomy of individual chromosomes. These four phenomena play an important role in generating genomic diversity in C. albicans.