Abstract

Meiotic crossovers form a physical link between the homologous chromosomes, thereby ensuring proper chromosome segregation and enhancing genetic diversity of the progeny. The frequency of crossovers is highly variable along the chromosomes in most species. Interestingly, the centromeres, which mediate attachment to microtubules via the kinetochores during cell divisions, are highly suppressed for crossovers in most eukaryotes. In crops including wheat, barley, rice and tomato recombination is highly skewed to distal regions of chromosomes, while large centromere proximal regions are devoid of crossovers. Unlocking recombination within these proximal regions might allow better introgression of traits during crop breeding. It is unknown why and how crossovers are suppressed in the centromeres, although proximal crossovers close to the centromeres may impact chromosome segregation during meiosis and thereby reduce fertility.

My project aims to understand the mechanisms that underlie recombination suppression in the vicinity of the centromeres in the model plant Arabidopsis thaliana. I am developing different approaches that utilize fluorescent markers (Traffic Lines) flanking centromeres, allowing for the visual identification of recombination in seeds. Firstly, after isolating large numbers of crossover events within the centromeric regions in wild type and mutant contexts (e.g. cmt3, met1 DNA methylation mutants), I will map their position at fine scale to study links between their distribution, DNA sequence (e.g. gene density, transposons, tandem repeats), and epigenetic marks (e.g. DNA methylation, H3K9me2). Secondly, I have performed a forward genetic screen to identify lines that, after chemical mutagenesis (EMS) might display increased/decreased recombination frequency in centromeric regions. Thirdly, I shall exploit natural variation by using different Arabidopsis accession in order to identify natural modifiers that affect centromeric recombination. Together these approaches will allow us to identify and characterize novel factors that regulate centromeric recombination.