The iron-responsive transcription factor HapX drives iron starvation adaptation and virulence in Talaromyces...

Talaromycosis is an opportunistic fungal infection caused by the thermally dimorphic fungus Talaromyces marneffei. During infection, T. marneffei survives within host phagocytic cells, where it encounters iron restriction and host-derived stress conditions. Therefore, regulation of iron homeostasis is essential for fungal adaptation and pathogenicity. HapX is a conserved bZIP transcription factor involved in iron-responsive regulation in several fungal species, but its role in T. marneffei has not been investigated. In this study, we examined the function of HapX in iron-dependent growth, stress tolerance, intracellular survival, and virulence in T. marneffei. ΔhapX deletion and complemented strains were constructed and analyzed under defined iron conditions in both mold and yeast phases. Deletion of hapX resulted in significant growth defects under iron-limited conditions, whereas growth under iron-replete conditions remained largely unchanged. The ΔhapX mutant showed reduced conidiation and impaired conidial germination. Transcriptional analysis revealed altered expression of iron-responsive genes, including reduced induction of siderophore biosynthesis genes, leading to reduce siderophore production. In addition to iron-dependent growth defects, loss of HapX increased sensitivity to cell wall and membrane stressors and selectively reduced tolerance to nitrosative stress in the yeast phase, while oxidative stress tolerance remained unchanged. The ΔhapX mutant exhibited increased susceptibility to amphotericin B. Importantly, deletion of hapX significantly reduced fungal survival within phagocytic amoeba and attenuated virulence in a Galleria mellonella infection model. Overall, our findings demonstrate that HapX contributes to the coordination of iron homeostasis, stress adaptation, and intracellular survival, which together support pathogenic fitness in T. marneffei.