The monothiol glutaredoxin GrxD is essential for sensing iron starvation in Aspergillus fumigatus

Abstract

Efficient adaptation to iron starvation is an essential virulence determinant of the most common human mold pathogen, Aspergillus fumigatus. Here, we demonstrate that the cytosolic monothiol glutaredoxin GrxD plays an essential role in iron sensing in this fungus. Our studies revealed that (i) GrxD is essential for growth; (ii) expression of the encoding gene, grxD, is repressed by the transcription factor SreA in iron replete conditions and upregulated during iron starvation; (iii) during iron starvation but not iron sufficiency, GrxD displays predominant nuclear localization; (iv) downregulation of grxD expression results in de-repression of genes involved in iron-dependent pathways and repression of genes involved in iron acquisition during iron starvation, but did not significantly affect these genes during iron sufficiency; (v) GrxD displays protein-protein interaction with components of the cytosolic iron-sulfur cluster biosynthetic machinery, indicating a role in this process, and with the transcription factors SreA and HapX, which mediate iron regulation of iron acquisition and iron-dependent pathways; (vi) UV-Vis spectra of recombinant HapX or the complex of HapX and GrxD indicate coordination of iron-sulfur clusters; (vii) the cysteine required for iron-sulfur cluster coordination in GrxD is in vitro dispensable for interaction with HapX; and (viii) there is a GrxD-independent mechanism for sensing iron sufficiency by HapX; (ix) inactivation of SreA suppresses the lethal effect caused by GrxD inactivation. Taken together, this study demonstrates that GrxD is crucial for iron homeostasis in A. fumigatus.

The Lysine Deacetylase RpdA Is Essential for Virulence in Aspergillus fumigatus

“…Expression of various genes under control of the xylP promoter in several mold fungi caused a loss-of-function phenotype under non-inducing conditions (Pongsunk et al, 2005; Hartmann et al, 2010; Sigl et al, 2010; Fazius et al, 2012; Gsaller et al, 2012; Bugeja et al, 2013; Baldin et al, 2015; Vaknin et al, 2016), e.g., growth of mutant strains expressing essential genes of the iron sulfur cluster biosynthetic machinery under control of the xylP promoter was completely blocked in non-inducing conditions in A. fumigatus (Misslinger et al, 2018). In contrast, use of the xylP promoter for expression of the essential monothiol glutaredoxin encoding grxD gene in A. fumigatus indicated leakiness of the xylP promoter dependent on the grxD allele (Misslinger et al, 2019). Most likely, the consequence of promoter leakiness, as monitored by growth pattern, depends on the gene expressed; i.e., it is affected by the required amount of the gene product, whereby the efficiency of expression is influenced by mRNA and protein stability, which are gene-specific features.…”

HapX, an Indispensable bZIP Transcription Factor for Iron Acquisition, Regulates Infection Initiation by Orchestrating Conidial Oleic Acid Homeostasis and Cytomembrane Functionality in Mycopathogen Beauveria bassiana

“…In filamentous fungi, transcription factor HapX plays a vital role in the fungus’ ability to handle iron starvation in the environment ( 38 ) by orchestrating complex metabolic pathways (e.g., siderophore synthesis) ( 39 , 40 ). In B. bassiana , BbHapX is also indispensable for fungal survival under iron starvation.…”

Carbon Catabolite Repression in Filamentous Fungi Is Regulated by Phosphorylation of the Transcription Factor CreA

“…Phosphoproteome analysis by LC-MS/MS. Proteome analysis, including phosphosite identification, was performed by nanoflow liquid chromatography coupled to tandem mass spectrometry (nLC-MS/ MS) as recently published (64).…”