Insight into trade-off between wood decay and parasitism from the genome of a fungal forest pathogen

Parasitism and saprotrophic wood decay are two fungal strategies fundamental for succession and nutrient cycling in forest ecosystems. An opportunity to assess trade-off between these strategies is provided by the major forest pathogen and wood decayer Heterobasidion annosum sensu lato.We report on the annotated genome sequence and transcript profiling as well as quantitative trait loci mapping of one member of the species complex; H. irregulare. Quantitative trait loci critical for pathogenicity and rich in transposable elements, orphan and secreted genes, were identified.A wide range of cellulose degrading enzymes is expressed during wood decay. In contrast, pathogenic interaction between H. irregulare and pine engages fewer carbohydrate active enzymes, but involves an increase in pectinolytic enzymes, transcription modules for oxidative stress, and secondary metabolite production.Our results show a trade-off in terms of constrained carbohydrate decomposition and membrane transport capacity during interaction with living host. The findings establish that saprotrophic wood decay and necrotrophic parasitism involve two distinct yet overlapping processes.