An ITS phylogeny of Leccinum and an analysis of the evolution of minisatellite-like sequences within ITS1

Bakker, H.C. den; Gravendeel, B.; Kuyper, T.W.


Phylogenetic relationships of the European species of Leccinum (Boletales, Boletaceae) were investigated by maximum parsimony, Bayesian and likelihood analyses of nrITS1-5.8S-ITS2 and 28S sequences. The separate gene trees inferred were largely concordant, and their combined analysis indicates that several traditional sectional and species-level taxonomic schemes are artificial. In Leccinum, the nrITS region ranges in size from 694 to 1480 bp. This extreme length heterogeneity is localized to a part of the ITS1 spacer that contains a minisatellite characterized by the repeated presence of CTATTGAAAAG and CTAATAGAAAG core sequences and mutational derivatives thereof. The number of core sequences present in the minisatellite varied from 12 to 36. Intra-individual sequence variation of the minisatellite was always smaller than between different species, indicating that concerted evolution proceeds rapidly enough to retain phylogenetic signal at the infraspecific level. In contrast, the evolutionary pattern exhibited by the major ITS1 repeat types found was homoplastic when mapped onto the species lineages inferred from the combined 5.8S-ITS2 sequences. The minisatellite therefore appears not to be useful for phylogeny reconstruction at or above the species level.