Analysis of phosducins in Hypocrea jecorina

The ascomycete Hypocrea jecorina (anamorph Trichoderma reesei) nowadays is the most important industrial producer of cellulases. These enzymes are regulated at the transcriptional level and one activator as well as two repressors of cellulase gene expression have been identified to date. Also carbon catabolite repression mediated by Cre1 was found to play an important role in this process. However, much less is known on how the environmental signal which leads to the adjustment of cellulase gene expression to altered conditions is transduced. Recent findings indicated that the transcription of the cellulase genes is significantly influenced by light and that this response is modulated by the PAS-domain protein ENVOY. Consequently, also the components of the common signaling pathway of heterotrimeric G-proteins, two G-alpha proteins have been analysed for their effect on cellulase gene expression as well as for the impact of light on their function. Indeed, instead of a direct, receptor- mediated function in induction of cellulase gene expression, a light dependent regulatory function in cellulase gene expression was found. This led to a more detailed analysis of this pathway, since the link between heterotrimeric G-protein signaling and light response could not yet be identified. This link would bring about the light signal and modulate the activity of the pathway accordingly by amplifying or attenuating the signal to be transduced. Primary candidates for such a function are the phosducin like proteins, which are known to modulate the strength of the G- protein signal by changing the availability of the G-beta-gamma subunits. Since the G-beta-gamma complex has been shown to influence the abundance of G-alpha subunits, a function of phosducins in cellulase regulation is likely. Studies on mammalian phosducins also revealed a function in the transduction of light signals, which has not yet been studied in fungi. The genome of Hypocrea jecorina comprises 2 open reading frames encoding proteins with significant similarities to characterized phosducins of other fungi. In this project the dependence of cellulase gene expression reflecting one of several output-pathways of heterotrimeric G-protein signaling on the class I phosducin will be subject to investigation. Therefore transcription of cellulases in the phosducin-deletion mutant strains under defined conditions of light and darkness, as well as the connection between the G-protein alpha and beta subunits and phosducins concerning (light-modulated) cellulase gene expression shall be analzyed. Based on these data the global targets of the postulated regulatory/signalling function of the phosducin proteins in Hypocrea jecorina shall be investigated and compared to effects of deletion of the G-protein beta and gamma subunits.

The ascomycete Hypocrea jecorina (anamorph Trichoderma reesei) nowadays is the most important industrial producer of cellulases. These enzymes are regulated at the transcriptional level and one activator as well as two repressors of cellulase gene expression have been identified to date. Also carbon catabolite repression mediated by Cre1 was found to play an important role in this process. However, much less is known on how the environmental signal which leads to the adjustment of cellulase gene expression to altered conditions is transduced. Recent findings indicated that the transcription of the cellulase genes is significantly influenced by light and that this response is modulated by the PASdomain protein ENVOY. Consequently, also the components of the common signaling pathway of heterotrimeric G-proteins, two G-alpha proteins have been analysed for their effect on cellulase gene expression as well as for the impact of light on their function. Indeed, instead of a direct, receptor- mediated function in induction of cellulase gene expression, a light dependent regulatory function in cellulase gene expression was found. This led to a more detailed analysis of this pathway, since the link between heterotrimeric G-protein signaling and light response could not yet be identified. This link would bring about the light signal and modulate the activity of the pathway accordingly by amplifying or attenuating the signal to be transduced. Primary candidates for such a function are the phosducin like proteins, which are known to modulate the strength of the G- protein signal by changing the availability of the G-beta-gamma subunits. Since the G-beta-gamma complex has been shown to influence the abundance of G-alpha subunits, a function of phosducins in cellulase regulation is likely. Studies on mammalian phosducins also revealed a function in the transduction of light signals, which has not yet been studied in fungi. The genome of Hypocrea jecorina comprises 2 open reading frames encoding proteins with significant similarities to characterized phosducins of other fungi. In this project the dependence of cellulase gene expression reflecting one of several output-pathways of heterotrimeric G-protein signaling on the class I phosducin will be subject to investigation. Therefore transcription of cellulases in the phosducin-deletion mutant strains under defined conditions of light and darkness, as well as the connection between the G-protein alpha and beta subunits and phosducins concerning (light-modulated) cellulase gene expression shall be analzyed. Based on these data the global targets of the postulated regulatory/signalling function of the phosducin proteins in Hypocrea jecorina shall be investigated and compared to effects of deletion of the G-protein beta and gamma subunits.