Understanding Repression Under Secretion Stress in Trichoderma reesei During Cellulase Expression.

Area of Science:

• Biotechnology
• Molecular Biology
• Industrial Microbiology

Background:

• Trichoderma reesei is crucial for industrial enzyme production.
• Cellular mechanisms balancing protein folding stress and secretion, like UPR and RESS, are not fully understood.

Purpose of the Study:

• To clarify the roles of UPR and RESS in T. reesei secretion.
• To investigate the relationship between UPR and RESS.
• To determine the regulatory level of RESS.

Main Methods:

• Exposure to dithiothreitol to induce UPR.
• Suppression of protein de novo synthesis to investigate UPR-RESS interaction.
• Transcription blocking experiments.
• Recombinant strain engineering (promoter and terminator exchange).
• Whole transcriptome analysis of industrial fermentations.

Main Results:

• Dithiothreitol increased UPR genes (≥6-fold) and decreased target genes (cbh1: ≥5-fold, egl2: ≥6-fold).
• RESS was observed even when UPR was suppressed, indicating a non-hierarchical relationship.
• RESS primarily acts at transcription initiation, not transcript stability.
• Recombinant strains with promoter exchange showed increased cbh1 transcript (≥45-fold), while terminator exchange did not.
• Industrial cellulase production revealed diverse hydrolytic enzyme induction and pathway adjustments, not UPR or RESS signatures.

Conclusions:

• UPR and RESS are distinct mechanisms in T. reesei secretion.
• RESS regulation occurs mainly at the transcriptional initiation level.
• Industrial enzyme production employs different strategies than those typically associated with UPR and RESS stress responses.