To identify enzymes that could be developed to reduce the recalcitrance of softwood resources, the transcriptomes of the softwood-degrading white-rot fungus Phanerochaete carnosa were evaluated after growth on lodgepole pine, white spruce, balsam fir, and sugar maple and compared to the transcriptome of P. carnosa after growth on liquid nutrient medium. One hundred fifty-two million paired-end reads were obtained, and 63% of these reads were mapped to 10,257 gene models from P. carnosa. Five-hundred thirty-three of these genes had transcripts that were at least four times more abundant during growth on at least one wood medium than on nutrient medium. The 30 transcripts that were on average over 100 times more abundant during growth on wood than on nutrient medium included 6 manganese peroxidases, 5 cellulases, 2 hemicellulases, a lignin peroxidase, glyoxal oxidase, and a P450 monooxygenase. Notably, among the genes encoding putative cellulases, one encoding a glycosyl hydrolase family 61 protein had the highest relative transcript abundance during growth on wood. Overall, transcripts predicted to encode lignin-degrading activities were more abundant than those predicted to encode carbohydrate-active enzymes. Transcripts predicted to encode three MnPs represented the most highly abundant transcripts in wood-grown cultivations compared to nutrient medium cultivations. Gene set enrichment analyses did not distinguish transcriptomes resulting from softwood and hardwood cultivations, suggesting that similar sets of enzyme activities are elicited by P. carnosa grown on different wood substrates, albeit to different expression levels.Softwood, which is generated by gymnosperm plant species, is the predominant form of land plant biomass in the Northern hemisphere (8). The plentiful renewable supply of wood makes it an attractive feedstock for many industrial uses, including biofuel production (18). Softwood is also among the most recalcitrant lignocellulosic feedstocks, particularly to bioprocess technologies (42). The recalcitrance of softwood lignocellulose to bioprocess technologies has been attributed to its higher lignin content, smaller pore size, and fewer hemicellulose-derived acetyl groups (25). Despite this recalcitrance, various microorganisms have evolved the ability to transform softwood fiber, the best studied of which are the white-rot and brown-rot fungi of the phylum Basidiomycota (13). White-rot fungi are the only microorganisms known to effectively degrade all components of lignocellulose, while brown-rot fungi depolymerize wood polysaccharides and leave the lignin as a modified residue (41).While the majority of white-rot fungi characterized to date effectively degrade hardwood, Phanerochaete carnosa is a white-rot fungus that was isolated almost exclusively from softwood (2). Previous analyses of proteins secreted by P. carnosa grown on spruce and cellulose identified peptides corresponding to enzymes involved in lignocellulose degradation, including cellulases, xylanases, glyoxal oxidases (GLOX), ...