Enhanced oxidative stress resistance in Ustilago maydis and its implications on the virulence

The phytopathogenic fungus Ustilago maydis causes corn smut by suppressing host plant defenses, including the oxidative burst response. While many studies have investigated how U. maydis responds to oxidative stress during infection, the consequences of heightened resistance to oxidative stress on virulence remain understudied. This study aimed to identify the effects on virulence in U. maydis strains exhibiting enhanced resistance to hydrogen peroxide (H₂O₂).To achieve this, we exposed U. maydis SG200 to 20 escalating H₂O₂ shocks, resulting in an adapted strain resistant to concentrations as high as 60 mM of H₂O₂, a lethal dose for the initial strain. Genetic analysis of the adapted strain revealed five nucleotide substitutions, two minor copy number variants, and a large amplification event on chromosome nine (1-149 kb) encompassing the sole catalase gene. Overexpressing catalase increased resistance to H₂O₂; however, this resistance was lower than that observed in the adapted strain. Additionally, virulence was reduced in both strains with enhanced H₂O₂ resistance.In summary, enhanced H₂O₂ resistance, achieved through either continuous exposure to the oxidative agent or through catalase overexpression, decreased virulence. This suggests that the response to the oxidative stress burst in U. maydis is optimal and that increasing the resistance to H₂O₂ does not translate into increased virulence. These findings illuminate the intricate relationship between oxidative stress resistance and virulence in U. maydis, offering insights into its infection mechanisms.