The role of Arabidopsis thaliana heterochromatin component H2A.W in meiotic recombination

In early meiosis, programmed-DNA double strand breaks occur throughout the genome which are predominantly repaired via homologous recombination. During this process, the homologous chromosomes pair and reciprocally exchange genetic information, also called crossovers. Crossovers break the linkage between genes and create new combinations of alleles which are inherited in the offspring population. Meiotic crossover events can be beneficial to plant breeding programmes, because they facilitate the introgression of alleles from wild crop relatives to elite cultivars. However, crossover distributions are non-random and with recombination preferentially enriched in distal regions of the chromosomes, and low numbers of crossovers in the interstitial and centromere-proximal regions. This is particularly true in plant species with large, repetitive genome, for example major crops such as maize and wheat. This considerably limits the potential to introduce allelic diversity throughout the genome during crop improvement. My study aims to provide novel insights in the control of meiotic recombination and to identify new factors involved in crossover repression across the centromere-proximal heterochromatic regions. Heterochromatin is compacted with a high DNA density and is enriched in nucleosome occupancy and specific chromatin modifications, including H3K9me2 and DNA methylation. Analysis of histone H2A variants via ChIP-sequencing has revealed that H2A.W is enriched in the heterochromatin. By combining cytogenetic, genetic and genomic assays, I have demonstrated that HTA7 is specifically involved in crossover repression within the pericentromeric and centromeric heterochromatin. The meiotic recombination phenotype of hta7 was not further increased in hta7 cmt3, where CHG DNA methylation and H3K9me2 are reduced, revealing an epistatic interaction between these epigenetic components. In the absence of all three H2A.W proteins, the elevation of recombination observed in hta7 was decreased and the organisation of the heterochromatin was changed, likely in response to the replacement of H2A.W by other canonical and variant histones. Overall, my study identified a new factor repressing meiotic recombination within Arabidopsis heterochromatin and provides new insights in the coordination between chromatin organisation and meiotic recombination.

Name dc:type.qualificationname

Doctor of Philosophy (PhD)

Level dc:type.qualificationlevel

Doctoral

Grantor dc:publisher.institution

University of Cambridge

Year dc:date.issued

2021

Author dc:creator

• Kuo, Pallas Ching-Yi

Advisor dc:contributor.advisor

• Henderson, Ian

• Chromatin
• Epigenetics
• Meiosis
• Recombination
• Crossover

Licence

• https://www.rioxx.net/licenses/all-rights-reserved/

Language dc:language

eng

DOI dc:identifier.doi

https://doi.org/10.17863/CAM.80204

OAI identifier oai:identifier

oai:www.repository.cam.ac.uk:1810/332767