Format: ORAL

Manuel Poretti1, Rimjhim Choudhury1, Yile Huang2, Hussein Anani2, Terezie Mandakova2, Martin Lysk2 and Christian Parisod1

1 Department of Biology, University of Fribourg, Fribourg, Switzerland 2 CEITEC Masaryk University, Brno, Czech Republic

Beyond their fundamental importance for the segregation of chromosomes, centromeres and their evolution remain elusive. In plants, flanking (pericentromeric) segments are characterized by low recombination and chiefly constituted of gypsy retrotransposons. Although such distribution expectedly results from an equilibrium between the insertion of new copies and their removal by purifying selection in high-recombining segments away from the centromere, empirical evidence remains scarce. Chromosome-scale assemblies characterizing the gene space and repetitive fraction of three diploids within the highly-polymorphic species Biscutella leavigata and one outgroup species were used to assess the evolution of retrotransposons around centromeres. Despite high synteny within the species, we find large variability in the non-coding part of the genome and particularly high sequence turnover among pericentromeric segments of the genome from the smallest population. By comparing retrotransposons actively targeting pericentromeric regions such as CRM elements to similarly-distributed retrotransposons that are unknown to present biased insertion such as ATHILA elements, we infer their dynamics of transposition vs deletion and highlight the role of specialized retrotransposons during a centromere shift. We further show that they disperse towards the distal part of nucleolar chromosomes and invade intervening gene-rich regions, increasing the methylation of nearby gene and decreasing their expression. Accordingly, bursts of retrotransposon activity associated with the rapid evolution of centromeres are not only affecting the formation and maintenance of heterochromatin and chromocenters, but also result in considerable changes across the gene space.