RAD51C-RAD51D interplays with MSH5 and regulates crossover maturation in rice meiosis.

Meiotic crossovers ensure accurate chromosome segregation and increase genetic diversity. RAD51C and RAD51D play an early role in facilitating RAD51 during homologous recombination. However, their later function in meiosis is largely unknown in plants. Here, through targeted disruption of RAD51C and RAD51D, we generated three new mutants and revealed their later meiotic role in crossover maturation. The rad51c-3 and rad51d-4 mutants showed a mixture of bivalents and univalents and no chromosomal entanglements, whereas rad51d-5 exhibited an intermediate phenotype with reduced chromosomal entanglements and increased bivalent formation compared with knockout alleles. Comparisons of RAD51 loadings and chromosomal entanglements in these single mutants, rad51c-3 rad51d-4, rad51c-3 dmc1a dmc1b, and rad51d-4 dmc1a dmc1b suggest that the retained level of RAD51 in mutants is required for uncovering their function in crossover formation. Reductions in chiasma frequency and later HEI10 foci in these mutants support that crossover maturation requires RAD51C and RAD51D. Moreover, interaction between RAD51D and MSH5 indicates that RAD51 paralogs may cooperate with MSH5 to ensure accurate Holliday junction processing into crossover products. This finding of the role of RAD51 paralogs in crossover control may be conserved from mammals to plants and advances our current understanding of these proteins.