Massive crossover elevation via combination of HEI10 and recq4a recq4b during Arabidopsis meiosis.

During meiosis, homologous chromosomes undergo reciprocal crossovers, which generate genetic diversity and underpin classical crop improvement. Meiotic recombination initiates from DNA double-strand breaks (DSBs), which are processed into singlestranded DNA that can invade a homologous chromosome. The resulting joint molecules can ultimately be resolved as crossovers. In Arabidopsis, competing pathways balance the repair of ∼100– 200 meiotic DSBs into ∼10 crossovers per meiosis, with the excess DSBs repaired as noncrossovers. To bias DSB repair toward crossovers, we simultaneously increased dosage of the procrossover E3 ligase gene HEI10 and introduced mutations in the anticrossovers helicase genes RECQ4A and RECQ4B. As HEI10 and recq4a recq4b increase interfering and noninterfering crossover pathways, respectively, they combine additively to yield a massive meiotic recombination increase. Interestingly, we also show that increased HEI10 dosage increases crossover coincidence, which indicates an effect on interference. We also show that patterns of interhomolog polymorphism and heterochromatin drive recombination increases distally towards the subtelomeres in both HEI10 and recq4a recq4b backgrounds, while the centromeres remain crossover suppressed. These results provide a genetic framework for engineering meiotic recombination landscapes in plant genomes.

Biotechnology and Biological Sciences Research Council (BBSRC) grant BB/L006847/1, BBSRC-Meiogenix IPA grant BB/N007557/1, European Research Area Network for Coodinating Action in Plant Sciences/BBSRC “DeCOP” (BB/M004937/1), Marie-Curie “COMREC” network FP7 ITN-606956, European Research Council (SynthHotspot CoG) and Gatsby Charitable Foundation (GAT2962), a Royal Society University Research Fellowship, and the Bettencourt Schueller Foundation.