Investigating the links between meiotic chromosome structure and homologous recombination in Arabidopsis thaliana

West, Allan (2015). Investigating the links between meiotic chromosome structure and homologous recombination in Arabidopsis thaliana. University of Birmingham. Ph.D.

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Abstract

Accurate chromosome segregation during meiosis requires the reciprocal exchange of DNA between homologous chromosomes, via a process called homologous recombination, resulting in the formation of crossovers (COs). This process begins with the formation of programmed DNA double-strand breaks (DSBs). Certain genomic loci, called hotspots, are more likely than others to produce DSBs. This is thought to be determined by various factors, which include post-translational histone modifications, such as H3K4 trimethylation. The histone methyl-transferase AtSDG2 is largely responsible for the deposition of this histone mark. This research shows that CO frequency and distribution are altered in an \(Atsdg2\) background. Study of a mutant allele of a gene which codes for a subunit of a histone-acetyl transferase complex, called AtMRG2, revealed a strongly reduced fertility phenotype and failure to produce DSBs. Further study revealed that the defects were due to mutation to the \(AtPRD3\) gene, known to be essential for DSB formation, and that the mutation to \(AtMRG2\) was not responsible. During meiosis, homologous recombination takes place in the context of specific structural arrangement of DNA organised as an array of loops emanating out from a proteinaceous axis, a major component of which is AtASY1. My studies demonstrate that the dynamics of AtASY1 are affected by mutation to AtPCH2, an AAA+ ATPase, and that formation of the synaptonemal complex is perturbed. \(Atpch2\)mutants initiate DSB formation and CO designation normally, but defects occur in CO maturation, causing a reduced CO frequency and formation of univalent chromosomes at metaphase I. Finally, the effects of temperature on the structure of meiotic chromosomes and homologous recombination were studied by cytological analysis of Col 0 and different meiotic mutants subjected to a range of temperatures for the duration of meiosis. I have demonstrated that certain mutations, such as \(Atsdg2\) and \(Atpch2\), confer some resistance to the effects of high (32˚C) temperature treatment, which causes various meiotic defects in Col 0.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

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