The Zn(II)2Cys6 transcription factor Ds Ace3 is a major activator of cellulases in the white-rot fungus Dichomitus squalens

ABSTRACT Plant biomass degradation by fungal extracellular enzymes is tightly controlled at the transcriptional level, enabling fungi to respond to the complex and variable composition of plant cell wall. White-rot basidiomycetes are of special interest due to their unique ability to degrade all components of lignocellulose, yet information on their transcriptional regulators involved in this process is highly limited. In this study, we characterized Ds Ace3, a Zn(II)2Cys6 transcription factor from the white-rot fungus Dichomitus squalens , predicted to be orthologous to the cellulase activators Ace3 of the ascomycete fungus Trichoderma reesei and Roc1 of the basidiomycete fungus Schizophyllum commune . Disruption of Ds Ace3 suppressed extracellular cellulase production and significantly impaired growth on cellulose and cellobiose. Transcriptomic analyses also confirmed that Ds Ace3 is essential for activating not only cellulase- and xylanase-encoding genes but also sugar transporter-encoding genes, linking enzyme production to sugar sensing and uptake. Ds Ace3 shows a strong phylogenetic and functional conservation compared to its ascomycete counterpart in T. reesei , a rare feature in known regulators of lignocellulose degradation. However, differences in the response of Ds Ace3 to lactose indicate distinct substrate sensing or signaling mechanisms in basidiomycetes. This study describes the first functional characterization of an Ace3 ortholog in a strongly ligninolytic white-rot fungus and provides critical insights into transcriptional regulation in white-rot fungi, facilitating advances in fungal applications for biomass conversion. IMPORTANCE White-rot basidiomycete fungi are key organisms in natural carbon cycling due to their unique ability to break down all polymeric components of wood. Despite their ecological and biotechnological importance, little is known about how these fungi control the genes responsible for this process. In this study, we characterized a transcription factor, Ds Ace3, in the white-rot fungus Dichomitus squalens . We show that Ds Ace3 is essential for activating genes needed to degrade cellulose and import the sugars released. Notably, Ds Ace3 shares functional conservation with similar regulators in both ascomycete and basidiomycete fungi. Our findings offer new insights into how wood-decaying white-rot fungi regulate plant biomass degradation and provide a molecular foundation for improving fungal enzyme production in industrial and environmental applications.