Abstract

Meiosis is a reductional division that produces gametes in sexually reproducing eukaryotes. During meiosis homologous chromosomes undergo reciprocal genetic exchange, known as crossover. As this process alters patterns of natural genetic variation it has evolutionary importance, in addition to serving as a tool for plant breeding. Crossover frequency is unevenly distributed along chromosomes. For example, gene-rich euchromatic regions undergo more crossovers than the repetitive heterochromatin close to the centromere. Heterochromatin is maintained by DNA methylation and is dramatically reduced in met1 DNA methyltransferase mutants. We have observed a extensive remodeling of crossover frequency in met1, including elevated centromeric, decreased pericentromeric and elevated distal crossovers. Interestingly total crossover events are the same between wild type and met1, indicating that homeostatic mechanisms mediate remodeling, including crossover interference. Using ‘pollen-typing’ we have identified a distally located intergenic crossover hotspot that shows elevated activity in met1, demonstrating that remodeling occurs via modulation of hotspot activity. Together these data demonstrate how regional epigenetic organization can pattern recombination frequency along eukaryotic chromosomes.