Analysis of cluster-type holocentromeres - a novel centromere-type identified in the Liliales genus Chionographis – How to get from mono- to holocentricity?

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The centromere is a specialized chromosomal region where the kinetochore complex assembles and spindle microtubules attach to ensure chromosome segregation during mitosis and meiosis. Different types of centromeres exist, although the function of the centromere is highly conserved. Recent analyses of species with non-classical centromeres demonstrated that in addition to monocentromeres, meta-polycentromeres and different types of holocentromeres independently evolved. The existence of closely related species with either holocentric or monocentric chromosome architecture offers a unique possibility for investigating the evolution of centromere types. Our study of Chionographis japonica (Liliales) revealed a new type of holocentromere organization. Unlike all other analyzed holocentric species possessing numerous small-sized centromere units, the holocentromere of C. japonica is composed of a low number of megabase-sized CENH3-positive satellite DNA arrays. To shed light on the transition from mono-to-holocentricity, we wish to perform a comparative analysis between holocentric C. japonica and the closely related monocentric species Chamaelirium luteum. Using a combination of different molecular, cytogenetic and bioinformatic tools, the following questions will be addressed. Does the kinetochore composition differ between holocentric C. japonica and monocentric C. luteum? How are the centromeric repeat arrays organized in C. luteum? Did the transition from mono-to-holocentricity reshuffle the genome of C. japonica? Did rolling circle amplification of centromeric repeats trigger the formation of a holocentromere? Did changes of inner centromere and pericentromeric histone modifications relate to the transition of centromere types?