Formation of interference-sensitive meiotic cross-overs requires sufficient DNA leading-strand elongation

Meiosis halves diploid genomes to haploid and is essential for sexual reproduction in eukaryotes. Meiotic recombination ensures physical association of homologs and their subsequent accurate segregation and results in the redistribution of genetic variations among progeny. Most organisms have two classes of cross-overs (COs): interference-sensitive (type I) and -insensitive (type II) COs. DNA synthesis is essential for meiotic recombination, but whether DNA synthesis has a role in differentiating meiotic CO pathways is unknown. Here, we show thatArabidopsis POL2A, the homolog of the yeastDNA polymerase-ε (a leading-strand DNA polymerase), is required for plant fertility and meiosis. Mutations inPOL2Acause reduced fertility and meiotic defects, including abnormal chromosome association, improper chromosome segregation, and fragmentation. Observation of prophase I cell distribution suggests thatpol2amutants likely delay progression of meiotic recombination. In addition, the residual COs inpol2ahave reduced CO interference, and the double mutant ofpol2awithmus81, which affects type II COs, displayed more severe defects than either single mutant, indicating thatPOL2Afunctions in the type I pathway. We hypothesize that sufficient leading-strand DNA elongation promotes formation of some type I COs. Given that meiotic recombination and DNA synthesis are conserved in divergent eukaryotes, this study and our previous study suggest a novel role for DNA synthesis in the differentiation of meiotic recombination pathways.