Independent evolution of betulin biosynthesis in Inonotus obliquus.

Inonotus obliquus, or, chaga mushroom, is a fungal species from the family Hymenochaetaceae (Basidiomycota) and is distributed across the boreal forest zone of the Northern Hemisphere. It causes aggressive white rot disease mainly among Betula family members, but upon suitable conditions can also infect other tree species. We assembled a high-quality 50.7 Mbp genome from Pacbio sequencing and identified a lineage-specific whole genome duplication event approximately 1.3 million years ago, which has contributed to a major increase in biochemical diversity in the species through preferential retention of cytochrome P450 superfamily members, among which are betulinate compounds that we analysed in depth.