Functional Study Of A Transcription Factor CaFlo8 In Morphogenesis And Virulence Of Candida Albicans

The dimorphic transition of yeast and hyphal forms is one of most determinants in Candida albicans for its pathogenicity. This transition is regulated by several signal transduction pathways. The transcription factor Flo8 is essential for filamentous growth in Saccharomyces cerevisiae and is regulated under the control of cAMP/protein kinase A (PKA) pathway. To determine whether a similar regulation exists in C. albicans, a C. albicans genomic DNA library was introduced into a S. cerevisiae haploid flo8 mutant and genes which could suppress invasive growth defect were isolated. In this screening, 8 novel genes were identified,including FLO8 ortholog CaFLO8(Candida albicans FLO8) and PPE1 ortholog CaPPE1(Candida albicans PPE1).Although low similarity between CaFlo8 and Flo8 in amino acid sequence, the CaFlo8 has a small region at N-terminus(amino acids 30-92) with very high similarity to that of Flo8(amino acids 72-154), which defined as LUFS domain. Expression of the CaFLO8 could complement the invasive growth defect of flo8 mutant in haploid cells and filamentous growth defect of diploid flo8 mutant cells. The CaFLO8 could also partially complement the defect of biofilm formation of flo8 mutant. The C. albicans FLO8 ortholog was confirmed by both sequence comparison and functional complementation. In S. cerevisiae, ectopic expression of the CaFLO8 could stimulate invasive/filamentous growth and the activation bypass MAPK pathway and cAMP/PKA pathway. The lacZ reporter system was used to analyze transcriptional activity of the CaFlo8. Different region of the CaFlo8 were fused to the lexA DNA binding domain, and the transcriptional activities of the fusion proteins were measured. Our data suggest that both the N-terminal LUFS domain and the C-terminal region are important for CaFlo8 function and the C-terminal region is the major transcriptional activation domain.Disruption of CaFLO8 had no significant effect on cell growth but led to dramatic defect in hyphal development. Caflo8/Caflo8 mutant cells were completely unable to respond to hyphal induction in all liquid hypha-inducing conditions and solid media examined. The Caflo8/Caflo8 mutants were also defective in the expression of hypha-specific genes. Partial defects in hyphal development and expression of hypha-specific genes were observed when one copy CaFLO8 was disrupted. The Caflo8/Caflo8 mutant is avirulent in a mouse model of systemic infection, and the...