Leibniz Institute of Plant Genetics and Crop Plant Research (IPK) OT Gatersleben, D-06466 Seeland, Germany.
Department of Plant Sciences, University of Cambridge, Cambridge CB2 3EA, UK.
J Exp Bot. 2021 Apr 2;72(8):3012-3027. doi: 10.1093/jxb/erab035.
Meiosis generates genetic variation through homologous recombination (HR) that is harnessed during breeding. HR occurs in the context of meiotic chromosome axes and the synaptonemal complex. To study the role of axis remodelling in crossover (CO) formation in a crop species, we characterized mutants of the axis-associated protein ASY1 and the axis-remodelling protein PCH2 in Brassica rapa. asy1 plants form meiotic chromosome axes that fail to synapse. CO formation is almost abolished, and residual chiasmata are proportionally enriched in terminal chromosome regions, particularly in the nucleolar organizing region (NOR)-carrying chromosome arm. pch2 plants show impaired ASY1 loading and remodelling, consequently achieving only partial synapsis, which leads to reduced CO formation and loss of the obligatory CO. PCH2-independent chiasmata are proportionally enriched towards distal chromosome regions. Similarly, in Arabidopsis pch2, COs are increased towards telomeric regions at the expense of (peri-) centromeric COs compared with the wild type. Taken together, in B. rapa, axis formation and remodelling are critical for meiotic fidelity including synapsis and CO formation, and in asy1 and pch2 CO distributions are altered. While asy1 plants are sterile, pch2 plants are semi-sterile and thus PCH2 could be an interesting target for breeding programmes.
减数分裂通过同源重组（HR）产生遗传变异，而 HR 是在繁殖过程中被利用的。HR 发生在减数分裂染色体轴和联会复合体的背景下。为了研究轴重塑在作物物种中的交叉（CO）形成中的作用，我们对与轴相关的蛋白 ASY1 和轴重塑蛋白 PCH2 的 Brassica rapa 突变体进行了特征描述。asy1 植物形成的减数分裂染色体轴无法联会。CO 形成几乎被废除，并且残余的交叉在末端染色体区域中按比例富集，特别是在核仁组织区域（NOR）携带的染色体臂中。pch2 植物显示出 ASY1 加载和重塑受损，因此只能实现部分联会，这导致 CO 形成减少和必需 CO 的丢失。PCH2 不依赖的交叉按比例向染色体远端区域富集。同样，在拟南芥 pch2 中，与野生型相比，CO 向端粒区域增加，而（peri-）着丝粒 CO 减少。总之，在 B. rapa 中，轴的形成和重塑对于减数分裂的保真度至关重要，包括联会和 CO 的形成，而在 asy1 和 pch2 中 CO 的分布发生了改变。虽然 asy1 植物是不育的，但 pch2 植物是半不育的，因此 PCH2 可能是一个有趣的育种目标。
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