The Aspergillus nidulans GATA Factor SREA Is Involved in Regulation of Siderophore Biosynthesis and Control of Iron Uptake

Abstract

A gene encoding a new GATA factor from Aspergillus nidulans, sreA, was isolated and characterized. SREA displays homology to two fungal regulators of siderophore biosynthesis: about 30% overall identity to SRE from Neurospora crassa and about 50% identity to URBS1 from Ustilago maydis over a stretch of 200 amino acid residues containing two GATA-type zinc finger motifs and a cysteine-rich region. This putative DNA binding domain, expressed as a fusion protein in Escherichia coli, specifically binds to GATA sequence motifs. Deletion of sreA results in derepression of L-ornithine-N5-oxygenase activity and consequently in derepression of the biosynthesis of the hydroxamate siderophore N,N',N"-triacetyl fusarinine under sufficient iron supply in A. nidulans. Transcription of sreA is confined to high iron conditions, underscoring the function of SREA as a repressor of siderophore biosynthesis under sufficient iron supply. Nevertheless, overexpression of sreA does not result in repression of siderophore synthesis under low iron conditions, suggesting additional mechanisms involved in this regulatory circuit. Consistent with increased sensitivity to the iron-activated antibiotics phleomycin and streptonigrin, the sreA deletion mutant displays increased accumulation of 59Fe. These results demonstrate that SREA plays a central role in iron uptake in addition to siderophore biosynthesis.