Role of mitogen-activated protein kinases (MAPKs) in cellulase formation.

Background: Despite being the most important cellulase producer, the cellulase-regulating carbon source signal transduction processes in are largely unknown. Elucidating these processes is the key for unveiling how external carbon sources regulate cellulase formation, and ultimately for the improvement of cellulase production and biofuel production from lignocellulose.

Results: In this work, the role of the mitogen-activated protein kinase (MAPK) signal transduction pathways on cellulase formation was investigated. The deletion of yeast -like in leads to improved growth and significantly improved cellulase formation. However, deletion has no effect on the transcription of cellulase-coding genes. The involvement of the cell wall integrity maintenance governing yeast Slt2-like Tmk2 in cellulase formation was investigated by overexpressing in to restore cell wall integrity. Transcriptional analysis found little changes in cellulase-coding genes between parent, , and strains. Cell wall integrity decreased in over the parent strain and restored in . Meanwhile, cellulase formation is increased in and then decreased in

Conclusions: These investigations elucidate the role of Tmk1 and Tmk2 on cellulase formation: they repress cellulase formation, respectively, by repressing growth and maintaining cell wall integrity, while neither MAPK regulates the transcription of cellulase-coding genes. This work, together with the previous investigations, suggests that all MAPKs are involved in cellulase formation, while Tmk3 is the only MAPK involved in signal transduction for the regulation of cellulase expression on the transcriptional level.