Induction of genes encoding plant cell wall-degrading carbohydrate-active enzymes by lignocellulose-derived monosaccharides and cellobiose in the white-rot fungus Dichomitus squalens

Fungi can decompose plant biomass to small oligo- and monosaccharides to be used as carbon sources. Some of these small molecules may induce metabolic pathways and production of extracellular enzymes targeted for degradation of plant cell wall polymers. Despite extensive studies in ascomycete fungi, little is known about the nature of inducers for the lignocellulolytic systems of basidiomycetes. In this study, we analyzed six sugars, known to induce expression of lignocellulolytic genes in ascomycetes, for their role as inducer in the basidiomycete white-rot fungus Dichomitus squalens using a transcriptomic approach. This identified cellobiose and L-rhamnose to be the main inducers of cellulolytic and pectinolytic genes, respectively, of D. squalens . Our results also identified differences in gene expression patterns between a dikaryotic and monokaryotic strain of D. squalens cultivated on plant biomass derived monosaccharides and the disaccharide cellobiose. This suggests that despite conservation of the induction between these two genetic forms of D. squalens , the fine-tuning in gene regulation of lignocellulose conversion is differently organized in these strains.