Evaluation of intragenomic polymorphism of ribosomal DNA ITS1 region in Taraxacum (Asteraceae: Crepidinae) by targeted NGS sequencing

The picture of intragenomic polymorphism of ITS1 region of rDNA repeats revealed by targeted high-throughput sequencing is a modern and simple method useful for phylogenetic purposes, and it can shed light on recent hybridizations. However, up to the present time it was not applied in Taraxacum, a taxonomically intricate genus with largely reticulate evolutionary pattern. We tested this approach on an exploratory set composed of 20 samples (8 species from 4 sections, including 5 species from the largest section Taraxacum), which were situated in different evolutionary and geographic distances from each other. Our results have shown that intragenomic polymorphism of ITS1 region of rDNA in Taraxacum may be successfully used for phylogenetic reconstructions. Species belonging to different sections were strikingly different by intragenomic polymorphism of rDNA, and substantial variability was also observed between some (but not all) specimens of section Taraxacum, giving preliminary evidence that this group may be not monomorphic. In the same time, 8 of 13 studied specimens from the section Taraxacum had ITS1 region substantially homogenized (dominant variant was at least 7 times more frequent than any other), which is considered connected with the age of the last hybridization event in corresponding lineages. Possibly, microspecies with substantially homogenized rDNA represent more strongly stabilized taxonomic units.