Kinetochore mutations and histone phosphorylation pattern changes preceded holo- and macro-monocentromere evolution

Abstract

Centromeres are essential for kinetochore assembly and spindle attachment. While chromosomes of most species are monocentric with a single centromere, a minority exhibit holocentricity, with a centromere along the chromatid length. Sporadic emergence of holocentricity suggests multiple independent transitions. To explore this, we compared the centromere and (epi)genome organization of two sister genera with contrasting centromere types: Chamaelirium luteum with large "macro-monocentromeres" and Chionographis japonica with holocentromeres. Both exhibit chromosome-wide histone phosphorylation patterns distinct from typical monocentric species. Kinetochore analysis revealed similar chimeric Borealin in both species, with additional KNL2 loss and NSL1 chimerism in Cha. luteum. The broad-scale synteny between both genomes supports de novo holocentromere formation in Chi. japonica. Despite sharing features with both centromere types, macro-monocentromeres do not represent a direct link between mono- and holocentromeres. We propose a model for the divergent evolution involving kinetochore gene mutations, altered histone phosphorylation patterns, and centromeric satellite DNA amplification.