Posttranscriptional regulation in Trichoderma

The ascomycete Trichoderma reesei is predominantly known for its efficient production of cellulolytic enzymes and heterologous proteins. While being a precisely studied model organism for plant cell wall degradation and increasingly also in light response, T. reesei is also one of the most important industrial workhorses, particularly in the biofuel industry. In recent years, investigation of the biology of this fungus revealed the influence of several important signal transduction pathways in regulation of cellulase gene expression. Heterotrimeric G-protein signaling exerts a considerable influence, which different in light and darkness, despite the presence of the same carbon source. Several studies moreover indicated that posttranscriptional pathways are involved in cellulase regulation. Transcriptome analyses on different carbon sources, light conditions and of light response and signaling mutants showed specific regulation of the translational machinery as well as energy metabolism. Traditionally, cellulase gene expression was considered to be regulated at the transcriptional level. Our analyses showed that two G-protein coupled receptors (GPCRs) are involved in substrate sensing in the presence of inducing carbon sources. Deletion of one of the two GPCRs caused a strong decrease in cellulase activity, but not transcription. Hence, the regulatory pathway triggering cellulase gene expression consists of a transcriptional section and a posttranscriptional section, which is targeted by the signaling pathway of heterotrimeric G-proteins. However, posttranscriptional processes have not yet been studied in T. reesei, neither in general nor with respect to enzyme production. Therefore we aim to investigate the relevance of selected posttranscriptional processes on cellulase gene expression and physiology of T. reesei. We will study genome wide mRNA stability of T. reesei cultures upon growth on cellulose as well as factors influencing stability. Moreover, we will investigate genes impacting translation and protein turnover. Hence, the proposed project shall provide intriguing new insights in to how a fungus reacts to its environment in an energy efficient manner and at the same time uncover new strategies for industrial strain improvement.

The ascomycete Trichoderma reesei is predominantly known for its efficient production of cellulolytic enzymes and heterologous proteins. While being a precisely studied model organism for plant cell wall degradation and increasingly also in light response, T. reesei is also one of the most important industrial workhorses, particularly in the biofuel industry. In recent years, investigation of the biology of this fungus revealed the influence of several important signal transduction pathways in regulation of cellulase gene expression. Heterotrimeric G-protein signaling exerts a considerable influence, which different in light and darkness, despite the presence of the same carbon source. Several studies moreover indicated that posttranscriptional pathways are involved in cellulase regulation. Transcriptome analyses on different carbon sources, light conditions and of light response and signaling mutants showed specific regulation of the translational machinery as well as energy metabolism. Traditionally, cellulase gene expression was considered to be regulated at the transcriptional level. Our analyses showed that two G-protein coupled receptors (GPCRs) are involved in substrate sensing in the presence of inducing carbon sources. Deletion of one of the two GPCRs caused a strong decrease in cellulase activity, but not transcription. Hence, the regulatory pathway triggering cellulase gene expression consists of a transcriptional section and a posttranscriptional section, which is targeted by the signaling pathway of heterotrimeric G-proteins. However, posttranscriptional processes have not yet been studied in T. reesei, neither in general nor with respect to enzyme production. In the course of this project we could show that the factors regulating the stability of mRNA impact in part also gene regulation of carbohydrate active enzymes, which degrade for example cellulose or xylan. Also the COP9 signalosome, the components of which are involved in regulation of protein stability, influence growth of T. reesei on diverse carbon sources as well as cellulase regulation. Finally our results also show that mRNA stability is altered by exposition to light or addition of glucose in this fungus.