Evolution of CenH3 Genes in Diploid and Allopolyploid Cotton Species

Centromeres are interesting and paradoxical structures that are highly variable in DNA content yet have an important and conserved function in chromosome segregation.  In most higher eukaryotes, centromeres largely consist of highly homogenized tandem repeats and retrotransposons that can vary greatly even among closely related species, which naturally leads to questions regarding the evolutionary dynamics of these necessary nuclear structures.  CenH3 is a centromere specific histone that plays a key role in centromere specification and is thought to coevolve with the highly variable centromeric repeats in order to preserve centromeric function.  Superimposed upon this is the observation that, although many organisms have experienced polyploidy in their evolutionary history, CenH3 typically is present in a single-copy in diploids and two copies in recent allotetraploid species. The genus Gossypium presents an opportunity to investigate the evolution of CenH3, and, by extension, the fate of centromeric repeats in recent allotetraploid species.  Gossypium contains a 1 – 2 million year old monophyletic clade of six polyploid species whose model diploid progenitors are well-established.  Preliminary analyses suggest that two copies of CenH3 are retained in polyploid Gossypium, and that the homoeologous copies are unequally expressed.  Here we present a phylogenetic analysis of CenH3 in diploid and polyploid plants that provides insight into centromeric evolution across angiosperms.