Lower level relationships in the mushroom genus Cortinarius (Basidiomycota, Agaricales): A comparison of RPB1, RPB2, and ITS phylogenies

We sampled and analyzed approximately 2900 bp across the three loci from 54 taxa belonging to a taxonomically difficult group of Cortinarius subgenus Phlegmacium. The combined analyses of ITS and variable regions of RPB1 and RPB2 greatly increase the resolution and nodal support for phylogenies of these closely related species belonging to clades that until now have proven very difficult to resolve with the ribosomal markers, nLSU and ITS. We present the first study of the utility of variable regions of the genes encoding the two largest subunits of RNA polymerase II (RPB1 and RPB2) for inferring the phylogeny of mushroom-forming fungi in combination with and compared to the widely used ribosomal marker ITS. The studied region of RPB1 contains an intron of the size and variability of ITS along with many variable positions in coding regions. Though almost entirely coding, the studied region of RPB2 is more variable than ITS. Both RNA polymerase II genes were alignable across all taxa. Our results indicate that several sections of Cortinarius need redefinition, and that several taxa treated at subspecific and varietal level should be treated at specific level. We suggest a new section for the two species, C. caesiocortinatus and C. prasinocyaneus, which constitute a well-supported separate lineage. We speculate that sequence information from RNA polymerase II genes have the potential for resolving phylogenetic problems at several levels of the diverse and taxonomically very challenging genus Cortinarius.