From minor loci to major players? Satellite DNA diversification in Crepis sensu stricto

Crepis sensu lato (s.l.) comprises species with remarkable variation in genome size, chromosome number, and karyotype structure, making this genus a valuable model for studying genome and chromosome evolution. Studies in various plant systems have suggested that diversification and speciation may be accompanied by dynamic changes in the repetitive DNA fraction, including satellite DNAs (satDNAs). A complex approach consisting of molecular (cloning, dot-blot and Southern hybridisation), cytogenetic (fluorescent in situ hybridisation) and phylogenetic methods allowed assessing the chromosomal and genomic organisation of three satDNAs in 32 species from Crepis s.l.. In the present study, we posed a question of whether these satDNAs are specific to C. capillaris, supporting the "birth-and-death" hypothesis, or whether they are also present in related species, consistent with the "library hypothesis". Each satDNA family exhibited different evolutionary trajectories. While pCcE9 amplification was specific to C. capillaris, supporting the "birth-and-death" hypothesis, two other analysed satDNAs were present in several related species, consistent with the "library hypothesis". Notably, pCcD29 showed different genomic and chromosomal organisation among C. capillaris and the species from the C. vesicaria group, suggesting that the satDNA evolution model proposed by Ruiz-Ruano et al. for animal systems may also apply to Crepis species. The organisation of the pCcD29 family ranges from numerous small, poorly homogenised loci (C. polymorpha) through organisation in both shorter and longer arrays (C. taraxacifolia) to a few major, highly homogenised loci (C. capillaris), highlighting contrasting evolutionary pathways of satDNAs within closely related species.