Monothiol glutaredoxin DaGrxB couples iron homeostasis with redox balance to orchestrate development and virulence in the peach shoot blight fungus Diaporthe amygdali

Peach shoot blight (PSB), caused by Diaporthe amygdali, is one of the most devastating fungal diseases affecting peach production worldwide. Glutaredoxins (Grxs) are ubiquitous redox-regulatory proteins involved in antioxidant defense and iron metabolism, yet their functions in phytopathogenic fungi remain largely unknown. Here, we identified four Grxs (DaGrxA-DaGrxD) in D. amygdali. Among them, DaGrxB, a monothiol glutaredoxin, is the sole member essential for vegetative growth, asexual reproduction and virulence. DaGrxB interacts with iron-regulatory transcription factors DaHapX and DaSreA and modulates their activities via iron-dependent nucleocytoplasmic shuttling, coordinating iron acquisition and storage gene expression. During infection, D. amygdali encounters a biphasic iron environment: an inherently iron-limited host environment at early stages (1-2 dpi) followed by host-mediated iron excess (3-4 dpi), and DaGrxB is essential for navigating this transition. Consistently, deletion of either DaHAPX or DaSREA significantly reduced virulence, confirming that iron homeostasis is a critical determinant of D. amygdali virulence. Notably, deletion of DaGRXB disrupts Fe-S cluster biosynthesis, causing mitochondrial Fe2+ accumulation, impaired aconitase activity, and reduced ATP production, which triggers constitutive activation of the GSH-dependent antioxidant system, with elevated GSH/GSSG ratios, increased GR and GST activities, and reduced H2O2 levels. Exogenous GSH and H2O2 depletion both reduced virulence, suggesting that disturbed redox balance directly contributes to attenuated virulence. Additionally, the Trx domain assists the Grx domain in nucleocytoplasmic translocation through intramolecular interactions. Finally, LDH-delivered dsRNA targeting DaGRXB effectively controls PSB. Collectively, these findings reveal how a monothiol glutaredoxin integrates iron homeostasis, redox balance and virulence in a plant pathogen, providing a foundation for RNAi-based disease management.