Analysis of cluster-type holocentromeres - novel centromere-types identified in the Liliales – How does evolutionary transition to holocentricity alter meiotic processes and recombination landscape?

• Applicant: Privatdozent Dr. Andreas Houben
• Subject Area: Plant Genetics and Genomics ; Evolution and Systematics of Plants and Fungi
• Term: since 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 436844938

The centromere is essential for the correct segregation of chromosomes. Besides chromosomes with a single primary constriction and a co-localised centromere (monocentromere), our previous studies revealed related species with alternative centromere types. In two sister genera of the plant tribe Chionographideae; Chionographis possesses line-like holocentromeres, and Chamaelirium carries unusually large, localized macro-monocentromeres. However, the mechanisms underlying evolutionary transitions between centromere types are poorly understood. Previously, we found in the Chionographideae tribe, that the formation of both centromere types was associated with mutations of kinetochore genes, with amplified centromeric satellite DNA, and with altered chromosome-wide histone phosphorylation patterns. Our preliminary analysis in Chi. japonica revealed a novel type of meiotic centromere and chromosome organization as a hitherto unknown adaptation to holocentricity. Moreover, in contrast to monocentric species including Cha. luteum, metaphase I bivalents of Chi. japonica exhibit a separation of sister centromeres, indicating an inverted order of sister chromatid separation. This unique configuration suggests a meiosis-specific reorganization of the holocentric chromosomes. The proposed project addresses the question of how meiosis in holocentric species differs from that in monocentric species and which spectrum of variation is possible in both systems. Two main work packages are envisaged: 1) investigating centromere behavior and chromatid dynamics during meiosis, including bouquet formation in both species, and determining whether holocentric Chi. japonica undergoes an inverted or canonical meiosis; 2) testing the recombination landscape by quantifying crossover frequency and distribution, analyzing the centromere effect (suppression of centromere-proximal crossovers) and crossover interference, and comparing meiotic genes of both species to those of typical monocentric species. The study will provide novel insights into the co-evolution of centromere organization and meiotic processes, and will broaden the knowledge of meiotic flexibility and centromere dynamics in species with unconventional centromeres.

• DFG Programme: Research Grants