GSE69461
Regulation of gene expression during the onset of ligninolytic oxidation by Phanerochaete chrysosporium on colonized wood
The biodegradation of lignocellulose requires the disruption of its lignin, which shields the metabolically assimilable polysaccharides in this recalcitrant natural composite. Although a variety of microorganisms can attack lignocellulose, white rot basidiomycetes are uniquely efficient at this process, cleaving the recalcitrant intermonomer linkages of lignin via extracellular oxidative mechanisms and mineralizing many of the resulting fragments to carbon dioxide via intracellular processes. Considerable progress has been made in understanding this process in the model white rot fungus Phanerochaete chrysosporium, which expresses important components of its ligninolytic system in response to nutrient limitation, as part of its secondary metabolism. Biochemical and genetic evidence point to an important role in P. chrysosporium for secreted lignin peroxidases (LiPs), manganese peroxidases (MnPs), and H2O2-producing oxidases, which are thought to work together to cleave lignin into low molecular weight fragments. However, many aspects of ligninolysis by P. chrysosporium remain poorly understood. Although a definitive picture of the entire ligninolytic system in P. chrysosporium is not yet attainable, transcriptome analyses of the fungus grown on wood can provide useful clues. With the advent of the initial genome assembly and annotations (v1.0 and v2.1), microarray-based transcriptome analysis allowed examination of transcript levels of P. chrysosporium genes when grown in ball-milled wood and in defined growth media. This approach provided useful insights but was limited to 10048 v2.1 targets and complicated by the unpredictable manner in which the fungus responds to unnatural carbon sources in submerged basal salts media. A complete, fully coordinated ligninolytic system is likely not expressed by P. chrysosporium on ball-milled wood, because a potential route for regulatory feedback has been eliminated: the cellulose and hemicellulose in this substrate is readily accessible to enzymes, and thus ligninolysis is not essential for growth. An alternative approach is to compare levels of gene expression just before and after the onset of secondary metabolism and extracellular substrate oxidation by P. chrysosporium as it utilizes solid wood as its carbon source. If this can be done, and decay of the substrate is also confirmed, then the genes undergoing marked changes in expression during the metabolic transition can be identified with greater confidence. Although not all such genes are expected to have roles in biodegradation, this strategy may identify interesting candidates for future investigation. Here we report RNAseq-based transcriptomes to characterize changes in gene expression that occur during the transition to ligninolytic metabolism. Overall design: Phanerochaete chrysosporium was inoculated onto thin sections of wood. RNA was purified from colonized material after 40 and 96 hours. Single read 100 bp Illumina runs were performed.