One of the most important features that enables Aspergillus fumigatus to grow within a susceptible individual and to cause disease is its ability to obtain Zn2+
ions from the extremely
zinc-limited environment provided by host tissues.
Zinc uptake from this source in A. fumigatus relies on ZIP transporters encoded by the zrfA, zrfB and zrfC genes. The expression of these genes is tightly regulated by the ZafA
transcription factor that regulates
zinc homeostasis and is essential for A. fumigatus virulence. We combined the use of microarrays, Electrophoretic Mobility Shift Assays (EMSA) analyses,
DNase I footprinting assays and in silico tools to better understand the regulation of the homeostatic and adaptive response of A. fumigatus to
zinc starvation. We found that under
zinc-limiting conditions, ZafA functions mainly as a transcriptional activator through binding to a
zinc response sequence located in the regulatory regions of its target genes, although it could also function as a repressor of a limited number of genes. In addition to genes involved in the homeostatic response to
zinc deficiency, ZafA also influenced, either directly or indirectly, the expression of many other genes. It is remarkable that the expression of many genes involved in
iron uptake and
ergosterol biosynthesis is strongly reduced under
zinc starvation, even though only the expression of some of these genes appeared to be influenced directly or indirectly by ZafA. In addition, it appears to exist in A. fumigatus a
zinc/
iron cross-homeostatic network to allow the adaptation of the fungus to grow in media containing unbalanced Zn:Fe ratios. The adaptive response to oxidative stress typically linked to
zinc starvation was also mediated by ZafA, as was the strong induction of genes involved in
gliotoxin biosynthesis and self-protection against endogenous
gliotoxin. This study has expanded our knowledge about the regulatory and metabolic changes displayed by A. fumigatus in response to
zinc starvation and has helped us to pinpoint new ZafA target genes that could be important for fungal pathogens to survive and grow within host tissues and, hence, for virulence.