The Molecular Underpinnings of Adaptive Evolution in Diatoms

Gilbertson, Reuben (2023) The Molecular Underpinnings of Adaptive Evolution in Diatoms. Doctoral thesis, University of East Anglia.

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Abstract

Diatoms are single-celled microalgae and are responsible for approximately half of all annual marine primary production. Thus, they play major roles in biogeochemical cycles and form the base of the marine food web. They are diverse with an estimated > 100,000 species and display high levels of genetic variability within natural populations, but the driving mechanisms are understudied. Mitotic recombination has been overlooked as a driver of genetic diversity due to a lower frequency of events compared to meiotic recombination. This thesis aims to elucidate the role of mitotic recombination in maintaining genome integrity and the generation of genetic diversity in diatoms by impairing homologous recombination (HR) through CRISPR/Cas.

Mitotic recombination is carried out by a suite of DNA repair genes which are highly conserved. Through extensive phylogenetic analysis in this thesis, the predicted core genes necessary for DNA pathways to function were identified in diatom genomes. However, differences in the conservation of X-family polymerases between diatom classes highlight potential evolutionary differences in repair mechanisms. To impair HR, the core DNA repair gene – BRCA2– was knocked out in the model diatom Thalassiosira pseudonana for the first time. Mutant cell lines showed increased sensitivity to induced DNA damage and were unable to adapt to high-temperature stress, confirming that BRCA2has a role in the repair of genetic mutations arising from induced or environmental stress. Comparative genomics revealed that loss of HR function in T. pseudonana resulted in increases in copy number variations (CNV) and copy-neutral loss of heterozygosity (LOH) events leading to fixation of mutations in mutant genomes. This increase in genomic instability allowed aneuploidy to progress from affecting small regions to whole chromosomes over time. This thesis presents novel data on the role of HR in maintaining genomic integrity and discuss its potential in the generation of genetic diversity in diatoms.

Item Type:	Thesis (Doctoral)
Faculty \ School:	Faculty of Science > School of Environmental Sciences
Depositing User:	Chris White
Date Deposited:	06 Jan 2025 14:49
Last Modified:	06 Jan 2025 14:49
URI:	https://ueaeprints.uea.ac.uk/id/eprint/98089
DOI:

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