Genome sequencing suggests sexual reproduction in Candida albicans

Meiosis is the hallmark process of sexual reproduction. Haploid cells are produced by the reduction of homologous chromosomes in diploid parental cells. The recent identification of a mating-type-like (MTL) locus in the human pathogenic yeast Candida albicans strongly suggests that this fungus, which has been historically thought of as being asexual, does in fact have a sexual cycle. The lack of knowledge of a sexual cycle in C. albicans has hindered the ability to carry out conventional genetic analyses on this organism. Recently, however, shotgun sequencing of the diploid C. albicans genome has been completed to 10.4 haploid genome equivalents (http://sequence-www.stanford.edu/group/candida). With this sequence, as well as the sequence of Saccharomyces cerevisiae and higher eukaryotic organisms, genome comparisons should provide an insight into the possibility that C. albicans uses a complete sexual cycle.Tzung et al.1xGenomic evidence for a complete sexual cycle in Candida albicans. Tzung, K. et al. Proc. Natl. Acad. Sci. U. S. A. 2001; 98: 3249–3253Crossref | PubMed | Scopus (134)See all References1 recently carried out such a genomic comparison between C. albicans, S. cerevisiae and some higher eukaryotes to search for homologues of genes known to be involved in meiosis. These investigators focused their search to genes crucial for mating and meiosis in budding yeast, as well as regulators known to be involved in cellular reproduction in higher eukaryotes. Using the BLASTP program, output was sorted and E-values of 1e−6 were used to assign homologues. Each sequence was also evaluated individually because there were some instances where biological data implied the presence of a particular homologue despite the lack of a gene with significant sequence homology. [Supplementary data summarizing the findings are available on the PNAS website (http://www.pnas.org)]. The genes identified were categorized according to their associated function: (1) mating differentiation; (2) nutritional control; (3) cell type control; (4) initiation of meiosis; (5) checkpoint control and progression through meiosis; (6) recombination and formation of synaptonemal complexes; and (7) spore wall morphogenesis and ascus formation. Five hundred genes analyzed by genome-wide transcriptional analysis of sporulation in S. cerevisiae were used as a reference point to begin the analysis.The presence of known S. cerevisiae homologues in C. albicans suggests similarities in the sexual cycle between these two fungi and the lack of known homologues of some genes highlights the interesting differences between them. With the identification of genes encoding homologues implicated in meiosis in C. albicans, a detailed functional characterization of each component should help to identify the role of these proteins and confirm the presence of a sexual cycle in this important human pathogen.