Recombination-coupled DNA synthesis facilitates post-invasion steps in meiotic crossover and noncrossover formations

During meiotic double-strand break (DSB) repair, most DSBs undergo tightly regulated 5' end resection, generating 3' single-stranded (ss) DNA tails, which assemble Rad51 and Dmc1 filaments to facilitate homology search and strand exchange for recombination. However, the occurrence of local DNA synthesis at the 3' end of the ssDNA in DSBs concerning the majority crossover and noncrossover processes at the DNA level and the involvement of DNA polymerase at the recombination site have remained unclear. Here, we investigated meiotic recombination-coupled DNA synthesis (MRDS) in Saccharomyces cerevisiae through a physical analysis of recombination events, timed incorporation of thymidine analogs, and super-resolution microscopy imaging. We demonstrate that DNA polymerase δ (Pol δ) is required to extend the initial D-loop through its end-primed synthesis activity. Importantly, Pol δ-mediated MRDS facilitates post-invasion steps for both double Holliday junction and noncrossover formations. We infer that MRDS is required for displacement-loop/single-end invasion extension through end-primed synthesis, ensuring accurate base pairing between the leading and complementary strands. This study highlights the critical role of Pol δ in MRDS and illustrates the robust regulation of recombination during the post-invasion stages.