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Molecular characterization of the proteinase-encoding gene, prb1, related to mycoparasitism by Trichoderma harzianum
R A Geremia1, G H Goldman, D Jacobs
1Laboratorium voor Genetica, Universiteit Gent, Belgium.
Abstract:
The soil fungus Trichoderma harzianum is a mycoparasitic fungus known for its use as a biocontrol agent of phytopathogenic fungi. Among other factors, Trichoderma produces a series of antibiotics and fungal cell wall-degrading enzymes. These enzymes are believed to play an important role in mycoparasitism. Among the hydrolytic enzymes, we have identified a basic proteinase (Prb1) which is induced by either autoclaved mycelia, fungal cell wall preparation or chitin; however, the induction does not occur in the presence of glucose. The proteinase was purified and biochemically characterized as a serine proteinase of 31 kDa and pI 9.2. Based on the sequence of three internal peptides, synthetic oligonucleotide probes were designed. These probes allowed subsequent isolation of a cDNA and its corresponding genomic clone. The deduced amino acid sequence indicates that the proteinase is synthesized as a pre-proenzyme and allows its classification as a serine proteinase. Northern analysis shows that the induction of this enzyme is due to an increase in the corresponding mRNA level.
Insights
Trichoderma harzianum produces a serine proteinase (Prb1) that aids in biocontrol. Its production is triggered by fungal components but suppressed by glucose, indicating a role in mycoparasitism.
Area of Science:
- Mycology
- Biochemistry
- Molecular Biology
Background:
- Trichoderma harzianum is a soil fungus utilized as a biocontrol agent against plant pathogens.
- Mycoparasitism by Trichoderma involves the production of enzymes that degrade fungal cell walls.
- Hydrolytic enzymes, particularly proteinases, are implicated in the mycoparasitic mechanism.
Purpose of the Study:
- To identify and characterize a novel proteinase from Trichoderma harzianum involved in mycoparasitism.
- To elucidate the regulation of this proteinase's expression.
Main Methods:
- Purification and biochemical characterization of the proteinase.
- Design of synthetic oligonucleotide probes based on peptide sequences.
- Isolation of cDNA and genomic clones.
- Northern blot analysis to assess mRNA levels.
Main Results:
- A basic serine proteinase (Prb1) of 31 kDa and pI 9.2 was purified.
- Prb1 production is induced by autoclaved mycelia, fungal cell wall preparations, or chitin.
- Glucose represses the induction of Prb1.
- The proteinase is synthesized as a pre-proenzyme.
- Enzyme induction correlates with increased mRNA levels.
Conclusions:
- Prb1 is a serine proteinase playing a role in the mycoparasitic activity of Trichoderma harzianum.
- The expression of Prb1 is regulated at the transcriptional level and is subject to nutritional control (glucose repression).