Hybridization-facilitated genome merger and repeated chromosome fusion after eight million years

Mandáková T, Guo X, Özüdoğru B, Mummenhoff K, Lysak MA

Plant Journal 96: 748-760.


The small genus Ricotia (9 species, Brassicaceae) is confined to the eastern Mediterranean. By comparative chromosome painting and a dated multi-gene chloroplast phylogeny we reconstructed the origin and subsequent evolution of Ricotia. The ancestral Ricotia genome originated through hybridization between two older genomes with n = 7 and n = 8 chromosomes, respectively, on the Turkish mainland during Early Miocene (c. 17.8 million years ago, Mya). Later the allotetraploid (n = 15) genome has been altered by two independent descending dysploidies (DD) to n = 14 in R. aucheri and the Tenuifolia clade (2 spp.). By Late Miocene (c. 10 Mya), the latter clade started to evolve in the most diverse Ricotia core clade (6 spp.) – the process preceded by a DD event to n = 13. Noteworthy, this dysploidy was mediated by a unique chromosomal rearrangement merging together the same two chromosomes as during the origin of a fusion chromosome within the paternal n = 7 genome c. 20 Mya. This shows that with a distance of c. 8 million years genome evolution can repeat itself and that structurally very similar chromosomes may originate repeatedly from the same ancestral chromosomes by different pathways (end-to-end translocation vs. nested chromosome insertion).