can also colonise roots of forest trees (pine, spruce, birch etc.) forming ectomycorrhiza-like symbiosis. The three species have the highest number of ABC genes among the species included in our analysis (Table 2 and Additional file 1). Interestingly, the number of ABC genes in these species negatively correlates with the genome size. O. maius has the highest number of ABC genes (72 genes), but the smallest genome assembly size, whereas M. bicolor has the lowest number of ABC genes among the three species, but the largest genome (Additional file 1).