The Microbial Metabolite Wuyiencin Potentially Targets Threonine Dehydratase in <i>Didymella segeticola</i> to Achieve Control of Tea Leaf Spot

Tea leaf spot caused by <i>Didymella segeticola</i> is a disease that has recently been discovered in the tea plantations of Southwest China and that has a significant negative impact on the yield and quality of tea leaves. Wuyiencin is a nucleotide antimicrobial that is effective against a range of fungal diseases. However, its mode of action is still unclear. The current study found that wuyiencin inhibited the mycelial growth of <i>D. segeticola</i> in vitro. Meanwhile, in vivo experiments confirmed that wuyiencin had a significant curative effect on tea leaf spot. Microscopic observation indicated that it damaged the organelles and nucleus in fungal cells. Reverse transcription quantitative PCR assays revealed that mycelium treated with wuyiencin at the half-maximal effective concentration (EC₅₀) dosage for 1 h exhibited 3.23 times lower expression of <i>threonine dehydratase</i> (<i>td</i>) gene, which is responsible for producing pyruvate. The wild-type (WT) strain had a 1.77-fold higher pyruvate concentration than that in the <i>td</i> mutant (<i>P</i> < 0.05). The <i>td</i> mutant was more sensitive than the WT to wuyiencin treatment, with the EC₅₀ value in the <i>td</i> mutant being 30.01 μg/ml compared with 82.34 μg/ml in the WT. Molecular docking demonstrated that wuyiencin bound to td, with a binding energy of -10.47 kcal/mol. Compared with the WT strain, wuyiencin significantly reduced ATP concentration of the <i>td</i> mutant strain at dosages of 80.0 and 160.0 µg/ml. In total, wuyiencin reduced td activity, inhibited pyruvate production, and decreased ATP content in the phytopathogenic fungus, ultimately disturbing the growth of the mycelium.