Thaldh3-Dependent GABA Metabolism Modulates Response of Trichoderma to Fusaric Acid-Induced Oxidative Stress

Fusaric acid (FSA) is a mycotoxin produced by pathogenic <i>Fusarium</i> species that inhibits the growth of various beneficial microbes. In this study, we investigated the molecular mechanisms by which <i>Trichoderma harzianum</i> NJAU4742 (<i>Th</i>), a beneficial fungus, responds to FSA-induced stress. Here, by combining a transcriptome analysis, a gene knockout, and physiological data measurements, our study investigated the molecular mechanisms underlying the response of <i>Trichoderma harzianum</i> NJAU4742 (<i>Th</i>) to FSA stress. The results showed that FSA can induce severe oxidative stress in <i>Th</i>, and an aldehyde dehydrogenase (<i>Thaldh3</i>) in <i>Th</i> plays a critical role in alleviating FSA stress. Deleting <i>Thaldh3</i> significantly decreased the γ-aminobutyrate (GABA) content, causing more severe oxidative damage in <i>Th</i>. Furthermore, we also provide evidence demonstrating that <i>Thaldh3</i> alleviates FSA stress by enhancing the activities of key enzymes involved in the tricarboxylic acid cycle and ATP content. A pot experiment showed that an enhanced tolerance to FSA increased the <i>Th</i> biomass, strengthening its antagonistic capacity against pathogens and reducing the disease index in tomatoes. In conclusion, these observations provide new insight into the role of beneficial microbes in promoting plant health.