Comparative Analysis of Sequence Composition and Structure of Centromeres in Two Pisum Species

Centromeres are essential structures for proper chromosome segregation during cell division. However, the relationship between centromere structure, sequence composition and function is still unclear. To study these questions, we adopted a model system of two closely related pea species. Garden pea (Pisum sativum) mitotic chromosomes harbor unique centromeres with multiple functional domains embedded within an extended primary constriction. Also, the sequence composition of the pea centromere differs from any other species studied so far. Pea centromeres are composed of thirteen families of satellite repeats differing in their monomer length. None of the families are present on all chromosomes and individual CenH3 domains on a single chromosome often contain different repeats. Using CenH3 antibody, we detected elongated centromeres also in some of the chromosomes of tawny pea (P. fulvum), a wild relative of the garden pea. To identify repetitive sequences in both genomes, we employed similarity-based clustering of genomic NGS reads. Subsequently, we identified repeats associated with CenH3 domains using ChIP-seq. Although the overall repeat composition of the two species is very similar, the spectrum of satellites associated with centromeric chromatin is partially different. In order to follow evolutionary changes in centromeres of individual chromosomes, we have identified homeologous chromosomes in the two pea species using P. sativum x P. fulvum F1 hybrids. We believe that our comparative work combining molecular cytogenetics and genomics will enable us to obtain insight into the role of the repetitive elements in the structure and function of plant centromeres.