Abstract
BackgroundTrichoderma reesei is a saprophytic fungus implicated in the degradation of polysaccharides present in the cell wall of plants. T. reesei has been recognized as the most important industrial fungus that secretes and produces cellulase enzymes that are employed in the production of second generation bioethanol. A few of the molecular mechanisms involved in the process of biomass deconstruction by T. reesei; in particular, the effect of sugar transporters and induction of xylanases and cellulases expression are yet to be known.ResultsIn our study, we characterized a novel sugar transporter, which was previously identified by our group through in silico analysis of RNA-seq data. The novel T. reesei 69957-sugar transport system (Tr69957) is capable of transporting xylose, mannose, and cellobiose using a T. reesei 69957-sugar transport system in Saccharomyces cerevisiae. The deletion of Tr69957 in T. reesei affected the fungal growth and biomass accumulation, and the sugar uptake in the presence of mannose, cellobiose, and xylose. Molecular docking studies revealed that Tr69957 shows reduced protein–ligand binding energy for interactions towards disaccharides in comparison with monosaccharides. Furthermore, the deletion of Tr69957 affected the gene expression of cellobiohydrolases (cel7a and cel6a), β-glucosidases (cel3a and cel1a), and xylanases (xyn1 and xyn2) in the cultures of parental and mutant strains in the presence of cellobiose and sugarcane bagasse (SCB).ConclusionThe transporter Tr69957 of T. reesei can transport cellobiose, xylose, and mannose, and can affect the expression of a few genes encoding enzymes, such as cellulases and xylanases, in the presence of SCB. We showed for the first time that a filamentous fungus (T. reesei) contains a potential mannose transporter that may be involved in the degradation of cellulose.
Highlights
The fungus Trichoderma reesei is one of the most studied microorganisms and is known for its ability to degrade lignocellulose [1]
Considering all the parameters provided by the I-TASSER platform, the chosen model for the Tr69957 (Fig. 1a) was predicted based on the template 4ZWB.A [human glucose transporter GLUT3 (N45T mutant) with bound d-glucose, outward-occluded conformation], which was determined by Deng et al [39]
The present study aimed to improve our understanding of the sugar transport systems, through characterization of a novel sugar transporter involved in the degradation of lignocellulosic biomass in T. reesei
Summary
The fungus Trichoderma reesei is one of the most studied microorganisms and is known for its ability to degrade lignocellulose [1]. A complex carbon source such as sugarcane bagasse (SCB), which is the major residue form the Brazilian agroindustry and constituted by cellulose (40–50%), hemicellulose (25–35%), and lignin (15–20%), can be efficiently degraded by fungal enzymes to release key regulatory molecules that might in turn activate the expression of genes to improve the sensing of different carbon sources and secretion of cellulolytic enzymes [5, 6]. The A. nidulans transporter XtrD was shown to be able to transport several other monosaccharides, in addition to xylose and glucose [11] After the uptake, these sugars have been shown to play an important role in metabolic signaling in the presence of cellulose [12]. A few of the molecular mechanisms involved in the process of biomass deconstruction by T. reesei; in particular, the effect of sugar transporters and induction of xylanases and cellulases expression are yet to be known
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