The histone deacetylase Hda1 affects oxidative and osmotic stress response as well as mycoparasitic activity and secondary metabolite biosynthesis in .

The mycoparasitic fungus is applied in agriculture as a biostimulant and biologic control agent against fungal pathogens that infest crop plants. Secondary metabolites are among the main agents determining the strength and progress of the mycoparasitic attack. However, expression of most secondary metabolism-associated genes requires specific cues, as they are silent under routine laboratory conditions due to their maintenance in an inactive heterochromatin state. Therefore, histone modifications are crucial for the regulation of secondary metabolism. Here, we functionally investigated the role of the class II histone deacetylase encoding gene of by targeted gene deletion, phenotypic characterization, and multi-omics approaches. Deletion of did not result in obvious phenotypic alterations but led to an enhanced inhibitory activity of secreted metabolites and reduced mycoparasitic abilities of against the plant-pathogenic fungi and . The mutants emitted altered amounts of four volatile organic compounds along their development, produced different metabolite profiles upon growth in liquid culture, and showed a higher susceptibility to oxidative and osmotic stress. Moreover, deletion affected the expression of several notable gene categories such as polyketide synthases, transcription factors, and genes involved in the HOG MAPK pathway.IMPORTANCEHistone deacetylases play crucial roles in regulating chromatin structure and gene transcription. To date, classical-Zn dependent-fungal histone deacetylases are divided into two classes, of which each comprises orthologues of the two sub-groups Rpd3 and Hos2 and Hda1 and Hos3 of yeast, respectively. However, the role of these chromatin remodelers in mycoparasitic fungi is poorly understood. In this study, we provide evidence that Hda1, the class II histone deacetylases of the mycoparasitic fungus , regulates its mycoparasitic activity, secondary metabolite biosynthesis, and osmotic and oxidative stress tolerance. The function of Hda1 in regulating bioactive metabolite production and mycoparasitism reveals the importance of chromatin-dependent regulation in the ability of to successfully control fungal plant pathogens.