How Tiny Genome Repeats Tell a Story in Heliophila's Evolution

The Heliophila plant family, with over 100 species, is the most diverse in the Brassicaceae lineage. It's mostly found in southern Africa, near two biodiversity hotspots. A close relative, Chamira, has a unique trait: it keeps its seed leaves. Researchers found a big genome change, like a duplication, happened about 26-29 million years ago in Heliophila, before it split from Chamira. This change led to a simplification of the genome, species spreading out, and new branches in the family tree. Scientists checked this effect on repeated DNA sections using low-coverage whole-genome data from 15 Heliophila species and Chamira. Despite different lifestyles and split into four main groups, genome sizes and repeat content were similar across Heliophila species. Long terminal repeat (LTR) retrotransposons were common, but tandem repeats were less so. In Chamira, however, tandem repeats were as abundant as LTR retrotransposons. In Heliophila, only 16 out of 108 tandem repeats were shared among species. None were shared with Chamira. Six shared repeats between clades suggested a common ancestor, while repeats specific to clades A and C supported their separate evolution. Three repeats in all clade A species backed recent diversification. A repeats-based tree partially matched the known Heliophila branches.