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

Yonglin Wang,Longyan Tian,Steven J Klosterman,Dianguang Xiong,Chengming Tian,Chenglin Deng,Aaron P Mitchell

doi:10.1128/msphere.00400-18

Abstract

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, Verticillium dahliae Deletion of VdHapX impaired mycelial growth and conidiation under both iron starvation and iron sufficiency. Furthermore, disruption of VdHapX led to decreased formation of the long-lived survival structures of V. dahliae, known as microsclerotia. Expression of genes involved in iron utilization pathways and siderophore biosynthesis was misregulated in the ΔVdHapX strain under the iron-depleted condition. Additionally, the ΔVdHapX strain exhibited increased sensitivity to high iron concentrations and H2O2, indicating that VdHapX also contributes to iron or H2O2 detoxification. The ΔVdHapX strain showed a strong reduction in virulence on smoke tree seedlings (Cotinus coggygria) and was delayed in its ability to penetrate plant epidermal tissue.IMPORTANCE 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 V. dahliae.

Highlights

Iron homeostasis is essential for full virulence and viability in many pathogenic fungi
Iron homeostasis is primarily maintained by two transcription factors in filamentous fungi, including the basic-leucine zipper (bZip) transcription factor, HapX, and the GATA zinc finger transcription factor, SreA, which are interconnected by a negative transcriptional feedback loop, i.e., in Aspergillus nidulans [3, 4] and Aspergillus fumigatus [5]
We revealed that VdHapX is crucial for virulence and detoxification to iron or H2O2 excess and affects microsclerotium formation. These results demonstrated a key role of VdHapX in iron homeostasis, virulence, and H2O2 detoxification in V. dahliae

Summary

Introduction

Iron homeostasis is essential for full virulence and viability in many pathogenic fungi. 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, Verticillium dahliae. Expression of genes involved in iron utilization pathways and siderophore biosynthesis was misregulated in the ΔVdHapX strain under the irondepleted condition. IMPORTANCE 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 V. dahliae. HapX represses SreA-mediated iron utilization pathways and activates siderophore biosynthesis for iron uptake [5,6,7]. Once the plant is infected, no available fungicides can effectively treat the disease [14]

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