Major Trends in Genome Evolution of Crucifers

The Brassicaceae family comprises 320 genera and over 3,600 species classified into some 50 bona fide monophyletic tribes belonging to three major phylogenetic lineages. The feasibility of comparative cytogenetic analyses and the available whole-genome sequences for a dozen of crucifer species (e.g., Arabidopsis lyrata, Brassica oleracea, B. rapa, Camelina sativa, Schrenkiella parvula) allowed us to reconstruct ancestral genomes and infer prevalent trends in genome evolution in the Brassicaceae.

Two major ancestral genomes, ACK with n=8 and PCK with n=7, were inferred for lineage I and II tribes, respectively. PCK seems to be derived from ACK through chromosome number reduction n=8 to n=7 (descending dysploidy) and multiple independent dysploidy events (n=8 to n=7, 6 and 5) marked the karyotype evolution across the family. While the ancestral karyotypes remained conserved in a number of extant species, in other groups they were reshuffled by translocations and inversions during descending dysploidy events. Only one chromosome fission event was documented during evolution of Brassicaceae taxa analyzed so far. In tribes which experienced recent whole-genome duplication events, the extent and tempo of genome reshuffling towards diploidized genomes exceed that observed in true diploid genomes. Descending dysploidy events were mediated by reciprocal translocations accompanied by a centromere loss or through end-to-end translocations and centromere inactivation.

This work was supported by the European Social Fund (CZ.1.07/2.3.00/20.0189).