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

Crepis sensu lato 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). In Crepis sensu stricto , research on satDNAs has so far been limited to C. capillaris , in which three highly abundant satDNAs have been identified. 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 , the amplification of the two other repeats was observed in several related species. 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 be applicable to plants. According to this model, the emergence of a new satDNA is initiated by de novo duplication, followed by the dissemination of short repeat arrays across the genome. Subsequent local amplification results in the formation of major satDNA loci. The repeats in these major loci undergo further amplification and “concerted evolution”, leading to sequence homogenisation. In contrast, the number of repeats in minor loci gradually decreases, falling below the FISH sensitivity.