Regulatory networks affected by iron availability in Candida albicans

Iron, an essential element for almost every organism, serves as a regulatory signal for the expression of virulence determinants in many prokaryotic and eukaryotic pathogens. Using a custom Affymetrix GeneChip representing the entire Candida albicans genome, we examined the changes in genome-wide gene expression in this opportunistic pathogen as a function of alterations in environmental concentrations of iron. A total of 526 open reading frame (ORF) transcripts are more highly expressed when the levels of available iron are low, while 626 ORF transcripts are more highly expressed in high-iron conditions. The transcripts dominantly affected by iron concentration range from those associated with cell-surface properties to others which affect mitochondrial function, iron transport and virulence-related secreted hydrolases. Moreover gene expression as assayed in DNA microarrays confirms and extends reports of alterations in cell-surface antigens and drug sensitivity correlated with iron availability. To understand how these genes and pathways might be regulated, we isolated a gene designated SFU1 that encodes a homologue of the Ustilago maydis URBS1, a transcriptional repressor of siderophore uptake/biosynthesis. Comparisons between wild-type and SFU1-null mutant strains revealed 139 potential target genes of Sfu1p; many of which are iron-responsive. Together, these results not only expand our understanding of global iron regulation in C. albicans, but also provide insights into the potential role of iron availability in C. albicans virulence.