Unleashing meiotic crossovers in hybrid plants.

Meiotic crossovers shuffle parental genetic information, providing novel combinations of alleles on which natural or artificial selection can act. However, crossover events are relatively rare, typically one to three exchange points per chromosome pair. Recent work has identified three pathways limiting meiotic crossovers in that rely on the activity of FANCM [Crismani W, et al. (2012) 336:1588-1590], RECQ4 [Séguéla-Arnaud M, et al. (2015) 112:4713-4718], and FIGL1 [Girard C, et al. (2015) 11:e1005369]. Here we analyzed recombination in plants in which one, two, or all three of these pathways were disrupted in both pure line and hybrid contexts. The greatest effect was observed when combining and mutations, which increased the hybrid genetic map length from 389 to 3,037 cM. This corresponds to an unprecedented 7.8-fold increase in crossover frequency. Disrupting the three pathways did not further increase recombination, suggesting that some upper limit had been reached. The increase in crossovers is not uniform along chromosomes and rises from centromere to telomere. Finally, although in wild type recombination is much higher in male meiosis than in female meiosis (490 cM vs. 290 cM), female recombination is higher than male recombination in (3,200 cM vs. 2,720 cM), suggesting that the factors that make wild-type female meiosis less recombinogenic than male wild-type meiosis do not apply in the mutant context. The massive increase in recombination observed in hybrids opens the possibility of manipulating recombination to enhance plant breeding efficiency.