Trichoderma guizhouense is a fungus used to protect plants from harmful pathogens. Researchers discovered that a special protein called TgZct4 acts like a master switch that activates the fungus’s defense system against harmful reactive oxygen molecules. When the fungus encounters stress, TgZct4 turns on genes that produce protective enzymes called catalases and superoxide dismutases, helping the fungus survive. This discovery could help scientists create even more effective biological pest control products.