Abstract
The complex environment of fungi requires a delicate balance between the efforts to acquire nutrition, to reproduce, and to fend off competitors. In Trichoderma reesei, an interrelationship between regulation of enzyme gene expression and secondary metabolism was shown. In this study, we investigated the physiological relevance of the unique YPK1-type kinase USK1 of T. reesei. Usk1 is located in the vicinity of the SOR cluster and is involved in regulation of several genes from this secondary metabolite cluster as well as dihydrotrichotetronine and other secondary metabolites. Moreover, USK1 is required for biosynthesis of normal levels of secondary metabolites in liquid culture. USK1 positively influences cellulase gene regulation, secreted cellulase activity, and biomass formation upon growth in constant darkness on cellulose. Positive effects of USK1 on transcript abundance of the regulator of secondary metabolism, vel1, and the carbon catabolite repressor gene cre1 are in agreement with these functions. In summary, we found that with USK1, T. reesei comprises a unique kinase that adds an additional layer of regulation to the connection of secondary metabolism and enzyme production in fungi.
Highlights
Plant cell wall degrading enzymes are largely co-regulated in T. reesei (Foreman et al, 2003) and their expression is regulated by a network of transcription factors (Benocci et al, 2017), of which XYR1, ACE3, and the carbon catabolite repressor CRE1 are most important
As one of the most important biotechnological workhorses among filamentous fungi, the physiology of T. reesei and its secondary metabolism are of high interest to industry
USK1 is related to YPK-type protein kinases which are essential for cell growth and maintenance of cell wall integrity (Chen et al, 1993; Roelants et al, 2002)
Summary
T. reesei is a model organism for regulation of plant cell wall degradation due to its efficient machinery for regulation and secretion of carbohydrate active enzymes (Saloheimo and Pakula, 2012; Gupta et al, 2016; Paloheimo et al, 2016). Plant cell wall degrading enzymes are largely co-regulated in T. reesei (Foreman et al, 2003) and their expression is regulated by a network of transcription factors (Benocci et al, 2017), of which XYR1, ACE3, and the carbon catabolite repressor CRE1 are most important. Trichoderma reesei has a long tradition of application in industry and received generally regarded as safe (GRAS) status (Nevalainen et al, 1994). Secondary metabolism of T. reesei became an interesting field of investigation and some interconnections with enzyme production became obvious, highlighting the importance
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