New mechanisms of evolution in sedges

Chromosomes, bundles of DNA common to all plants and animals, are held together and controlled via a central area called a centromere. Some plants and animals have a centromere diffused across the length of the chromosome; these chromosomes are referred to as holocentric.

Recent evidence suggests that holocentric chromosomes influence the evolution of the species in which they occur. An EU-funded project, 'Holocentric chromosome evolution and the origins of biodiversity in a hyper-diverse plant lineage' (HOLOCHROMEVOL), is investigating this phenomenon in the common European sedge genus Carex.

Carex is an interesting genus: chromosome rearrangements have resulted in large genetic differences within species as well as broad lineage diversity (more than 2 000 species). The genus has holocentric chromosomes, and so it is likely that these have influenced genetic diversity in the genus.

The project has conducted long-term breeding experiments with Carex, both within and between species. Several generations of offspring were grown, interbred and harvested for further analysis.

High-throughput genetic sequencing was used to evaluate chromosome rearrangements and how this phenomenon related to interbreeding in these plants. Researchers have found that germination rate decreases as chromosomal rearrangements increase.

This is the first evidence that holocentric chromosomes can influence the breeding (and thus the evolution) of an organism. HOLOCHROMEVOL has produced an in vivo model for other scientists to study the relationships between holocentric chromosomes, evolution and speciation.