Loss of DNA methylation affects recombination landscape in Arabidopsis

During sexual reproduction half of the genetic material is deposited in gametes and a complete set of chromosomes is restored upon fertilisation. Reduction of the genetic information prior gametogenesis occurs in meiosis where crossovers (COs) between homologous chromosomes secure an exchange of their genetic information. COs are not evenly distributed along chromosomes and are suppressed in chromosomal regions encompassing compact, hypermethylated centromeric and pericentromeric DNA. Therefore, it has been postulated that DNA hypermethylation is inhibitory to COs. Here by analysing meiotic recombination in mutant plants with hypomethylated DNA we observed unexpected and counterintuitive effects of the DNA methylation losses on COs distribution, further promoting recombination in the naturally hypomethylated euchromatic chromosome arms, while inhibiting it in heterochromatic regions encompassing centromeric and pericentromeric hypermethylated DNA. Importantly, the total number of COs was not affected, implying that the loss of DNA methylation only led to a global redistribution of COs along chromosomes. To determine by which mechanisms altered levels of DNA methylation influenced recombination, namely whether this occurred directly in cis or indirectly in trans by changing expression of genes encoding recombination components, we analysed COs distribution in WT lines with randomly scattered and well mapped hypomethylated chromosomal segments. Results of these experiments, supported by expression profiling data, suggest that DNA methylation affects meiotic recombination in cis. As DNA methylation is subjected to significant variation even within a single species, our results implicate that it could influence evolution of plant genomes through the control of meiotic recombination. 2 samples: Col, epiRIL12, with 3 replicates each