[Characterization of Candida albicans ferric reductase genes in response to environmental stresses].

Objective: Ferric reductases play a central role in iron acquisition and mobilization in C. albicans. This study focuses on stress response strategies exhibited by several ferric reductase genes through function and expression analyses.
Methods: Northern blot analysis was used to examine ferric reductase genes expression levels in different iron deficiency. We constructed ferric reductase-null mutants by a PCR-based homologous recombination, and examined the effects of gene deletion on cell-surface ferric reductase activity and growth ability under different conditions. Sub-cellular localization of Frpl-GFP fusion was imaged and analyzed by confocal laser scanning fluorescence microscopy.
Results: FRE10 was highly expressed at acidic pH, compared to that at alkaline pH, whereas the expression of FRE2 was just the opposite. Deletion of FRE10 resulted in a significant decreased surface reductase activity at acidic pH, with 75.5% down-regulation compared to wild-type levels. The fre2delta/delta mutant showed significantly attenuated growth ability and cell-surface ferric reductase activity at alkaline pH. Sub-cellular localization revealed that the green fluorescence was accumulated in the vacuoles.
Conclusion: The expression of both FRE10 and FRE2 is induced in a pH-dependent manner. FRE2 encodes a major cell surface ferric reductase under alkaline pH condition. Frp1 localizes to the vacuole, and might support mobilization and transport of vacuolar ferric iron stores.