Promoter heterozygosity at the Candida albicans CHS7 gene is translated into differential expression between alleles

A characteristic genetic trait in Candida albicans is diploidism, which is accompanied by a high degree of natural heterozygosity. Here, we describe natural heterozygosity in the promoter of the CaCHS7 gene in the SC5314 strain, associated with a GC-rich sequence of 28 nucleotides. Both alleles are expressed in the wild type and contribute to the total levels of the CaCHS7 mRNA. However, the presence of this region in the promoter (L allele) significantly reduced the transcription of the gene as compared with its absence (S allele). Heterozygous strains containing either allele showed distinct phenotypic characteristics. The HeteroL strain showed reduced levels of chitin, a partial resistance to calcofluor, and a moderate degree of morphogenetic alterations in hypha-inducing media. The HeteroS strain was very similar to the wild type, showing only a modest decrease in chitin that did not appear to confer distinct phenotypic characteristics. This is therefore a new report about allelic heterogeneity in C. albicans, directly translated into differential regulation of both alleles, leading to phenotypic consequences. The allelic heterogeneity reported appears to be strain-specific. However, sequence comparison between strains indicated that this region is prone to genetic divergence, which is probably responsible for the reported allelic heterozygosity of CaCHS7.