Endogenous hydrogen sulfide reprograms mitochondrial respiration and modulates pathogenicity in Ustilago maydis

Sulfur metabolism is a central determinant of microbial physiology and adaptation to environmental conditions. Hydrogen sulfide (H 2 S), a reactive sulfur species produced during cysteine metabolism, has recently emerged as a key regulator of mitochondrial function and redox signaling. However, its role in phytopathogenic fungi and its potential impact on fungal pathogenic behavior remain poorly understood. Here, we show that metabolic conditions that enhance endogenous H 2 S production in the maize phytopathogen Ustilago maydis trigger coordinated cellular remodeling. Elevated intracellular H 2 S levels were associated with mitochondrial biogenesis, a shift from cytochrome-dependent respiration toward alternative oxidase (AOX)-mediated electron transport, and widespread proteomic reprogramming affecting mitochondrial, metabolic, and proteasomal pathways. These changes were accompanied by increased global protein S-sulfenylation and S-persulfidation, altered lipid distribution, and elevated hydrogen peroxide levels, indicating substantial remodeling of cellular redox homeostasis. Functional consequences of this metabolic state were evaluated in maize infection assays. Although infection rates were not significantly altered, plants infected with cells exhibiting elevated endogenous H 2 S levels displayed increased tumor formation and altered symptom progression. Together, our findings indicate that increased H 2 S production modulates mitochondrial respiration, redox regulation, and fungal pathogenic behavior in Ustilago maydis . This work highlights endogenous H 2 S as an important regulatory node connecting microbial metabolism with host-pathogen interactions.