The Transcription Factor VdHapX Controls Iron Homeostasis and Is Crucial for Virulence in the Vascular Pathogen Verticillium dahliae.

Iron homeostasis is essential for full virulence and viability in many pathogenic fungi. Here, we showed that the bZip transcription factor VdHapX functions as a key regulator of iron homeostasis for adaptation to iron-depleted and iron-excess conditions and is required for full virulence in the vascular wilt fungus, Deletion of impaired mycelial growth and conidiation under both iron starvation and iron sufficiency. Furthermore, disruption of led to decreased formation of the long-lived survival structures of , known as microsclerotia. Expression of genes involved in iron utilization pathways and siderophore biosynthesis was misregulated in the Δ strain under the iron-depleted condition. Additionally, the Δ strain exhibited increased sensitivity to high iron concentrations and HO, indicating that VdHapX also contributes to iron or HO detoxification. The Δ strain showed a strong reduction in virulence on smoke tree seedlings () and was delayed in its ability to penetrate plant epidermal tissue. This study demonstrated that VdHapX is a conserved protein that mediates adaptation to iron starvation and excesses, affects microsclerotium formation, and is crucial for virulence of .