Enhanced secretion of extracellular proteins in <i>Trichoderma reesei</i> through targeted deletion of a kinesin encoding gene

Trichoderma reesei is an important industrial cellulase producer, but its protein secretion is limited by elongated hyphae during bioreactor cultivation. Physical and process-based controls are widely applied to modulate fungal morphology, but genetic strategies remain poorly explored. Here, we show that deletion of kinesin gene kin1 alters hyphal growth and boosts cellulase production in T. reesei. Deletion of kin1 led to pronounced morphological changes: shorter, highly branched hyphae, compact colony architecture, and increased biomass. Under cellulase-inducing conditions, the Δkin1 strain exhibited higher cellulase titers and activities, improving biomass saccharification efficiency. Importantly, this enhanced performance was maintained during bioreactor fermentation, likely due to increased shear resistance from the altered morphology. Transcriptome analysis revealed that expression levels of major cellulase genes were largely unaffected by kin1 gene deletion, indicating that enhanced enzyme production occurs independently of transcriptional upregulation. Together, our findings uncover a previously unrecognized link between kinesin-mediated hyphal morphology and protein secretion in T. reesei. The kin1-deletion phenotype provides a genetic strategy for improving cellulase production in other filamentous fungi.