Meiotic Recombination in Arabidopsis Is Catalysed by DMC1, with RAD51 Playing a Supporting Role

Recombination establishes the chiasmata that physically link pairs of homologous chromosomes in meiosis, ensuring their balanced segregation at the first meiotic division and generating genetic variation. The visible manifestation of genetic crossing-overs, chiasmata are the result of an intricate and tightly regulated process involving induction of DNA double-strand breaks and their repair through invasion of a homologous template DNA duplex, catalysed by RAD51 and DMC1 in most eukaryotes. We describe here a RAD51-GFP fusion protein that retains the ability to assemble at DNA breaks but has lost its DNA break repair capacity. This protein fully complements the meiotic chromosomal fragmentation and sterility of Arabidopsis rad51, but not rad51 dmc1 mutants. Even though DMC1 is the only active meiotic strand transfer protein in the absence of RAD51 catalytic activity, no effect on genetic map distance was observed in complemented rad51 plants. The presence of inactive RAD51 nucleofilaments is thus able to fully support meiotic DSB repair and normal levels of crossing-over by DMC1. Our data demonstrate that RAD51 plays a supporting role for DMC1 in meiotic recombination in the flowering plant, Arabidopsis.重组可形成交叉结（chiasmata），在减数分裂（meiosis）过程中将成对同源染色体（homologous chromosomes）物理连接，确保其在第一次减数分裂中均等分离，并产生遗传变异。作为遗传交换（genetic crossing-overs）的可见表征，交叉结源自一套复杂且受严格调控的过程：包括诱导DNA双链断裂（DNA double-strand breaks），以及通过侵入同源模板DNA双链对断裂进行修复，该过程在大多数真核生物中由RAD51和DMC1催化。本研究描述了一种RAD51-GFP融合蛋白，该蛋白仍可在DNA断裂处组装，但丧失了DNA断裂修复能力。该蛋白可完全互补拟南芥（Arabidopsis）rad51突变体的减数分裂染色体碎片化与不育表型，但无法互补rad51 dmc1双突变体的相关缺陷。即便在RAD51催化活性缺失的情况下，DMC1仍是唯一具有活性的减数分裂链转移蛋白，但在互补后的rad51植株中未观察到遗传图谱距离发生变化。因此，无活性的RAD51核丝（nucleofilaments）的存在，足以支持减数分裂DNA双链断裂修复，以及DMC1介导的正常水平的遗传交换。本研究数据表明，在显花植物拟南芥的减数分裂重组过程中，RAD51对DMC1发挥辅助作用。