Control of homologous recombination in plant meiosis

Abstract

Meiotic homologous recombination is initiated by formation of programmed DNA double strand breaks (DSBs) via SPO11 topoisomerase-like complexes. Only a subset of meiotic DSBs are repaired to crossovers, thereby increasing genetic diversity in populations. Meiotic DSB and crossover recombination frequencies vary along eukaryotic chromosomes, with hotspots and are controlled by chromatin structure and DNA sequence. In addition, crossover number is strongly limited to ~1 to 3 along chromosomes by anti-crossover factors. By purifying and sequencing SPO11-1-oligonucleotides in Arabidopsis we found that DSB hotspots occurred preferentially in gene promoters, introns, terminators and specific DNA transposons, indicating that chromatin accessibility is a major determinant of meiotic DSB landscape in plants. Consistently, meiotic DSBs and crossovers are positively correlated at chromosome arms, but limited across pericentromeres and centromeres by DNA methylation and H3K9me2. We have isolated higher crossover rate (hcr) mutants as new anticrossover mutants via genetic screening by using seed-based fluorescent reporter system. The anticrossover mutants with increased crossovers will be presented in further detail.