During meiosis eukaryotes produce four haploid gametes from a single diploid parental cell. In meiotic S-phase homologous chromosomes, which were inherited from maternal and paternal parents, are replicated. Homologous chromosomes then pair and undergo reciprocal crossover, which generates new mosaics of maternal and paternal sequences. Meiosis also involves two rounds of chromosome segregation, meaning that only one copy of each chromosome is finally packaged into the resulting haploid gametes. In this work I sought to genetically engineer two elements of meiosis, in order to generate tools which may be useful for plant breeding. The first project sought to generate a second division restitution (SDR) population, where the second meiotic division is skipped. This is created by crossing an SDR mutant, omission of second division1, which produces diploid pollen due to a defective meiosis-II, to a haploid inducer line, whose chromosomes are lost from the zygote post-fertilisation. This was intended to give rise to diploid plants possessing chromosomes from just the SDR parent. Importantly, the SDR parent used was heterozygous, meaning that SDR progeny should show mostly homozygous chromosomes, but with regions of residual heterozygosity, determined by crossover locations. This project succeeded in creating a small number of plants with the predicted SDR genotype, although a range of aberrant genotypes were also observed. I present several hypotheses that could account for the observed progeny genotypes. In a second project I attempted to direct meiotic recombination using DNA double strand breaks targeted to specific sites. This project used a spo11-1 mutant, which is unable to produce the endogenous meiotic DNA DSBs that normally mature into crossovers. Instead, TALFokI nucleases (TALENs) were expressed from meiotic promoters in order to generate exogenous DSBs at sites determined by the DNA binding specificity of the TAL repeat domains. The project succeeded in transforming TALENs into spo11-1 mutants and confirming their expression. However, this was not sufficient to recover the spo11-1 mutant infertility or direct crossovers. Potential reasons for this non-complementation are discussed, as well as their implications for control of meiotic recombination in plant genomes.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:744497 |
| Date | January 2018 |
| Creators | Diaz, Patrick Loyola |
| Contributors | Henderson, Ian |
| Publisher | University of Cambridge |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | https://www.repository.cam.ac.uk/handle/1810/271685 |
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