Effect of the res-2 transcription factor gene deletion on protein secretion and stress response in the hyperproducer strain Trichoderma reesei Rut-C30

The fungus Trichoderma reesei is one of the most used industrial cellulase producers due to its high capacity of protein secretion. The strain was shown to possess an expanded endoplasmic reticulum, but the genetic factors responsible for this phenotype remain still unidentified. Recently, three new transcription factors were described in Neurospora crassa which were demonstrated to be involved in protein secretion. The orthologous gene of one of them, Res-2, was deleted in the T. reesei hyperproducer strain Rut-C30 and its role on protein secretion analyzed. The mutant strain showed slower growth on all substrates tested, but the presence of the stress agent DTT had contrasting effects. Protein secretion tended to be lower in the deletion strain compared to the parental strain Rut-C30. Analysis of the transcriptomes of the Rut-C30 and the ?res-2 mutant strain in secretion stress conditions reveiled remarkably few differences, but induction of cellulase secretion and/or presence of DTT led to differential expression of genes coding for transporters, redox genes and lipid metabolism. These results suggest that in the T. reesei Rut-C30 strain, Res-2 does not act as a master regulator of the secretion pathway, but contributes to a high protein secretion by adjusting the expression of genes involved in membrane turnover and the redox status of the organism or specific organelles. Overall design: Rut-C30 and the ?res-2 strain were cultivated in fed flasks and after a 48h batch phase on glucose medium, they were submitted to either a glucose (control condition) or lactose fed-batch. Two other conditions included the exposure to 10 mM DTT for 2 hours at the end of the glucose and the lactose fed-batch. All samples were run in duplicates and mycelia were collected after 48h of fed-batch for RNA extraction.