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Cellulase induction in Trichoderma reesei by cellulose requires its own basal expression
J C Carle-Urioste1, J Escobar-Vera, S El-Gogary
1Department of Biochemistry, Institute of Chemistry, University of São Paulo, Av. Prof. Lineu Prestes 748, São Paulo 05508-900, SP, Brazil.
The Journal of Biological Chemistry
|April 11, 1997
Summary
Basal cellulase activity in Trichoderma reesei is essential for inducing cellulase gene expression in response to cellulose. This study confirms that low levels of cellulase enable cellulose breakdown, triggering further enzyme production.
Area of Science:
- Molecular Biology
- Mycology
- Biochemistry
Background:
- The induction mechanism of cellulases by cellulose in Trichoderma reesei remains unclear.
- A previous hypothesis suggested basal cellulase activity initiates cellulose degradation, releasing trigger molecules.
- Understanding this process is crucial for optimizing industrial enzyme production.
Purpose of the Study:
- To investigate the role of basal cellulase expression in the induction of cellulase genes by cellulose in T. reesei.
- To provide experimental evidence supporting the proposed mechanism of cellulase induction.
- To identify rate-limiting steps in the cellulase synthesis pathway.
Main Methods:
- Quantification of cbh1 and egl1 transcripts in uninduced and cellulose-induced T. reesei.
- Functional analysis of the cbh1 promoter using a hygromycin B resistance gene construct.
- Assessment of cellulase gene expression using antisense RNA suppression.
Main Results:
- Transcripts for cbh1 and egl1 were detected in uninduced T. reesei cells.
- Cellulose induced cbh1 and egl1 transcript levels over 1100-fold.
- Basal cbh1 promoter activity was confirmed, and antisense RNA suppressed cellulose-induced transcription.
Conclusions:
- Basal expression of cellulase genes is necessary for cellulose-mediated induction in T. reesei.
- Extracellular cellulase activity acts as the rate-limiting factor in this induction process.
- The findings validate the model where low-level cellulase activity initiates a positive feedback loop for enzyme synthesis.