Isolation of the Candida albicans homologs of Saccharomyces cerevisiae KRE6 and SKN1: Expression and physiological function

Abstract

Cell wall β-glucan in a pathogenic fungus, Candida albicans, is highly branched with β-1,3 and β-1,6 linkages. We have isolated the C. albicans cDNAs for KRE6 and SKNI, the genes required for β-1,6-glucan synthesis in Saccharomyces cerevisiae. The results of Northern blot analysis revealed that C. albicans KRE6 was expressed at a higher level than SKNI in the yeast phase, while SKNI expression was strongly induced upon induction of hyphal formation. In addition, the C. albicans KRE6 and SKNI mRNAs but not the actin mRNA were shortened during the yeast-hypha transition. Unlike S. cerevisiae, more than 50% of cell wall glucan was β-1,6 linked in C. albicans. Neither β-1,3-glucan nor β-1,6-glucan was affected by the homozygous C. albicans skn1Δ null mutation. Although we never succeeded in generating the homozygous C. albicans kre6Δ null mutant, the hemizygous kre6Δ mutation decreased the KRE6 mRNA level by about 60% and also caused a more than 80% reduction of β-1,6-glucan without affecting β-1,3-glucan. The physiological function of KRE6 was further examined by studying gene regulation in C. albicans. When KRE6 transcription was suppressed by using the HEX1 promoter, C. albicans cells exhibited the partial defect in cell separation and increased susceptibility to Calcofluor White. These results demonstrate that KRE6 plays important roles in β-1,6-glucan synthesis and budding in C. albicans.