New Insights into Meiotic Recombination from Analyses of DNA Synthesis Gene Functions

Meiosis halves diploid genomes to haploid and is essential for sexual reproduction in eukaryotes. Meiotic recombination ensures the proper segregation of homologous chromosomes and also results in the redistribution of genetic materials among progeny. DNA synthesis is essential for meiotic recombination, but the molecular mechanisms of DNA synthesis in meiotic recombination are largely unknown. We previously used RNA-seq to investigate the Arabidopsis male meiocytes and found many DNA synthesis genes with higher expression at meiocytes, suggesting their potential roles in meiosis. Further studies using molecular genetic, cell biological and biochemical approaches provided strong evidence that lagging strand DNA synthesis genes are required for the formation of meiotic interference-sensitive crossovers (COs), supporting the idea that meiotic recombination requires lagging strand DNA synthesis. Moreover, genome re-sequencing analyses in both yeast and plants showed that meiotic gene conversion tracts vary in length, ranging from several hundreds to thousands of nucleotides and that tracts associated with CO are usually longer than those of NCO. This raises a question whether there is any difference in DNA synthesis among CO-associated tracts with different lengths. Analyses of the largest subunit of DNA polymerase ε, important for leading strand elongation, demonstrated that it has a role in promoting formation of a portion of meiotic interference-sensitive COs, suggesting that sufficient leading strand DNA elongation could be a critical step of interference-sensitive/insensitive CO differentiation. Together, given that meiotic recombination and DNA synthesis are highly conserved in divergent eukaryotes, our studies suggest a novel role for DNA synthesis in the differentiation of meiotic recombination pathways.