Plant centromeres: genetics, epigenetics and evolution.

The centromere is a functional locus of the chromosome responsible for chromatid cohesion and segregation in cell division. Usually, the centromeres can be distinguished from the remaining chromosomal regions either in structure, as they are heterochromatic constrictions that divide the chromosome in two arms, or in molecular constitution, as they have an exclusive H3 histone variant and specific DNA sequences. Besides being essential for genetic stability of eukaryotes, centromere is particularly interesting since it plays conserved roles but show high variability on organization and DNA composition. Centromeres are usually composed by satellite repeats and retrotransposons and the sequences can differ even among closely related species. Some unusual configurations containing single copy DNA were also described, including even some transcribed genes. In this review, we discuss molecular constitution, epigenetics and different types of centromere, with emphasis on plant centromeres. We also present recent advances about evolutionary processes involved in origin and differentiation of centromeres.