Temporal transcriptome analysis of the white-rot fungus Obba rivulosa shows expression of a constitutive set of plant cell wall degradation targeted genes during growth on solid spruce wood

The basidiomycete white-rot fungus Obba rivulosa, a close relative of Gelatoporia (Ceriporiopsis) subvermispora, is an efficient degrader of softwood. The dikaryotic O. rivulosa strain T241i (FBCC949) has been shown to selectively remove lignin from spruce wood prior to depolymerization of plant cell wall polysaccharides, thus possessing potential in biotechnological applications such as pretreatment of wood in pulp and paper industry. In this work, we studied the time-course of the conversion of spruce by the genome-sequenced monokaryotic O. rivulosa strain 3A-2, which is derived from the dikaryon T241i, to get insights to transcriptome level changes during prolonged solid state cultivation. During 8-week cultivation, O. rivulosa expressed a constitutive set of genes encoding putative plant cell wall degrading enzymes. High level of expression of the genes targeted towards all plant cell wall polymers was detected at 2-week time point, after which majority of the genes showed reduced expression. This implicated non-selective degradation of lignin by the O. rivulosa monokaryon. These results suggest high variation between mono- and dikaryotic strains of the white-rot fungi with respect to their abilities to convert plant cell wall polymers. The aim of the study is to study nutritional demands during a prolonged cultivation on wood by looking at the transcriptome at different time points, with special interes at CAZymes and central carbon metabolic genes. Obba rivulosa 3 A-2 growing on its natural substrate, spruce wood sticks was studied after 2, 4 and 8 weeks of solid state cultivation in order to follow wood depolymerization in more natural like conditions.