Functional analysis of C₂H₂ zinc finger transcription factor CrzA involved in calcium signaling in Aspergillus nidulans

Calcium signaling systems are widely employed in eukaryotes and are implicated in the regulation of diverse biological processes. Calcineurin is an important signaling component, which mediates ion homeostasis and virulence in several fungi. Based on intensive studies conducted on budding yeast, transcription factor Crz1p is thought to be a target of calcineurin. To provide insight into calcium signaling, a Crz1p homolog (CrzA) in a filamentous fungus Aspergillus nidulans was identified and its function with special reference to calcium response was characterized. A crzA gene disruption mutant exhibited sensitivity to high concentrations of Mn²⁺ and Ca²⁺, and mediated the expression of P-type calcium-ATPase homologous genes. Comprehensive transcriptional analysis with DNA microarrays indicated that CrzA regulates the expression of a vacuolar Ca²⁺/ H⁺ exchanger gene in response to external calcium stimuli. It is suggested that the calcineurin-CrzA pathway is the mediator of Ca²⁺ homeostasis in A. nidulans. Moreover, a crzA/hogA double mutant showed hypersensitivity to osmotic stress, indicating the importance of calcium homeostasis for adaptation to osmotic stress, a universal stress in filamentous fungi.