Studies on sugar transporter CRT1 reveal new characteristics that are critical for cellulase induction in Trichoderma reesei

Abstract

Background Trichoderma reesei is an ascomycete fungus that has a tremendous capability of secreting extracellular proteins, mostly lignocellulose-degrading enzymes. Although many aspects of the biology of this organism have been unfolded, the roles of the many sugar transporters coded in its genome are still a mystery with a few exceptions. One of the most interesting sugar transporters that has thus far been discovered is the cellulose response transporter 1 (CRT1), which has been suggested to be either a sugar transporter or a sensor due to its seemingly important role in cellulase induction. Results Here we show that CRT1 is a high-affinity cellobiose transporter, whose function can be complemented by the expression of other known cellobiose transporters. Expression of two sequence variants of the crt1 gene in Saccharomyces cerevisiae revealed that only the variant listed in the RUT-C30 genome annotation has the capability to transport cellobiose and lactose. When expressed in the $$\Delta$$ Δ crt1 strain, the variant listed in the QM6a genome annotation offers partial complementation of the cellulase induction, while the expression of the RUT-C30 variant or cellobiose transporters from two other fungal species fully restore the cellulase induction. Conclusions These results add to our knowledge about the fungal metabolism of cellulose-derived oligosaccharides, which have the capability of inducing the cellulase production in many species. They also help us to deepen our understanding of the T. reesei lactose metabolism, which can have important consequences as this sugar is used as the inducer of protein secretion in many industrial processes which employ this species.

Factors regulating cellulolytic gene expression in filamentous fungi: an overview

“…The Crt1 protein is now recognized as a high affinity transporter of cellobiose and lactose, similar to its analog in N. crassa Cdt1 and is believed to play a critical role in the cellulase induction signaling cascade. [ 158 ].…”

Disruption of alpha-tubulin releases carbon catabolite repression and enhances enzyme production in Trichoderma reesei even in the presence of glucose

“…The most significantly upregulated gene was gene ID 69957 or Tr69957 (log2 fold change = 6.15), reported as a cellobiose, mannose and xylose transporter [34]. ID 3405 or crt1, reported as a cellobiose and sophorose transporter which plays a key role in the cellulolytic signaling process [35,36], showed the highest gene expression level of the significantly expressed transporters. ID 50894 or str1, reported as a transporter induced by pentose, ID 121482 or str2, reported as a transporter with broad substrate specificity [37], and ID 79202 and 77517, reported as a lactose transporter [38], were all upregulated in PC-3-7ΔtubB.…”

Elimination of the Sugar Transporter GAT1 Increased Xylanase I Production in Trichoderma reesei

“…Whereas a number of T . reesei sugar transporters have been characterized regarding their in vitro activities in transporting sugars released from lignocellulose hydrolysis ( Saloheimo et al, 2007 ; Ivanova et al, 2013 ; Zhang et al, 2013 ; Huang et al, 2015 ; Sloothaak et al, 2016 ; Nogueira et al, 2018 ; Havukainen et al, 2020 , 2021a , b ), relatively few of them have been found to be involved in the regulation of lignocellulolytic enzyme production. In particular, the cellobiose transporter Crt1 plays an essential role in activation of cellulase genes in T .…”

“…In particular, the cellobiose transporter Crt1 plays an essential role in activation of cellulase genes in T . reesei , regardless of the inducing carbon sources used ( Ivanova et al, 2013 ; Zhang et al, 2013 ; Havukainen et al, 2020 ). Deletion of crt1 , however, does not compromise but improves xylanase production ( Zhang et al, 2013 ), implicating a difference in sugar transporter-involved induction mechanisms between cellulase and xylanase genes.…”