Holocentric organisms, unlike typical monocentric organisms, have
kinetochore activity distributed along almost the whole length of the
chromosome. Because of this, chromosomal rearrangements through fission
and fusion are more likely to become fixed in holocentric species, which
may account for their extraordinary rates of chromosome evolution.
Genome synteny has been reported to be conserved in animals with
holocentric chromosomes despite high rates of chromosome rearrangements.
Comparing genomes of Carex species and a genome of a distantly related
Cyperaceae we have characterised conserved vs. rearranged genome regions
across pairs of species that range in time since divergence between 2
and 50 million years. We have compared a C. scoparia genome with a
linkage map of the same species to study rearrangements at a population
level and suppression of recombination patterns. We found a surprisingly
conserved genome synteny even between very distantly related species and
extraordinarily high rates of chromosome evolution in genus Carex.
Comparing the distribution of repetitive DNA and gene density between
conserved and rearranged genomic regions, we found repetitive DNA to be
related to holocentromeres and as well as rearranged regions of the
genome. This evidence of extremely conserved synteny in sedges and the
massive events of chromosome fission and fusion found across the
evolution of genus Carex suggests the presence of common genomic
hotspots of chromosome evolution related to repetitive DNA.