背景回顾：The hexaploid bread wheat genome comprises over 16 gigabases of sequence across 21 chromosomes. Meiotic crossovers are highly polarized along the chromosomes, with elevation in the gene-dense distal regions and suppression in the Gypsy retrotransposon-dense centromere-proximal regions. 

主要研究：We profiled the genomic landscapes of the meiotic recombinase DMC1 and the chromosome axis protein ASY1 in wheat and investigated their relationships with crossovers, chromatin state, and genetic diversity. 

结果1：DMC1 and ASY1 chromatin immunoprecipitation followed by sequencing (ChIP-seq) revealed strong co-enrichment in the distal, crossover-active regions of the wheat chromosomes. Distal ChIP-seq enrichment is consistent with spatiotemporally biased cytological immunolocalization of DMC1 and ASY1 close to the telomeres during meiotic prophase I. DMC1 and ASY1 ChIP-seq peaks show significant overlap with genes and transposable elements in the Mariner and Mutator superfamilies. However, DMC1 and ASY1 ChIP-seq peaks were detected along the length of each chromosome, including in low-crossover regions. 

结果2：At the fine scale, crossover elevation at DMC1 and ASY1 peaks and genes correlates with enrichment of the Polycomb histone modification H3K27me3. This indicates a role for facultative heterochromatin, coincident with high DMC1 and ASY1, in promoting crossovers in wheat and is reflected in distalized H3K27me3 enrichment observed via ChIP-seq and immunocytology. 

结果1：Genes with elevated crossover rates and high DMC1 and ASY1 ChIP-seq signals are overrepresented for defense-response and immunity annotations, have higher sequence polymorphism, and exhibit signatures of selection. 

结论：Our findings are consistent with meiotic recombination promoting genetic diversity, shaping host–pathogen co-evolution, and accelerating adaptation by increasing the efficiency of selection.

 摘 要 

六倍体面包小麦基因组由21条染色体，超过16Gb的序列组成。减数分裂交换（crossover）在小麦染色体上的分布极不均匀，在基因密集的染色体末端区发生频率较高，而在富含Gypsy逆转座子的着丝粒附近区域被抑制。作者对小麦减数分裂重组酶DMC1和染色体轴相关蛋白ASY1在基因组上的结合位点进行了图谱分析，以探究这两个蛋白与染色体交换、染色质状态以及遗传多样性之间的关联。DMC1和ASY1蛋白的ChIP-seq数据显示，这两个蛋白的结合位点都会富集在小麦的染色体末端，即染色体交换发生频率较高的基因组区域。该结果与DMC1和ASY1蛋白在减数分裂前期I时，存在时空特异性地靠近端粒的细胞免疫沉淀定位一致。DMC1和ASY1的ChIP-seq峰值在Mariner和Mutator亚家族的基因和转座元件上存在显著重叠。但是，在小麦染色体上那些染色体交换发生频率很低的基因组区域也检测到了DMC1和ASY1的ChIP-seq峰值。通过精细的分析，作者发现在DMC1和ASY1存在峰值的区域，染色体交换频率的提升与Polycomb组蛋白H3K27me3修饰的富集有关。这些结果说明，兼性异染色质（即在一定的细胞类型或一定的发育阶段呈现凝集状态的异染色质）与高水平的DMC1和ASY1一起，促进小麦的染色体交换，并且可以通过ChIP-seq和免疫细胞学所观测到的H3K27me3富集来反应这种兼性异染色质。与染色体交换频率提升、高水平DMC1和ASY1蛋白ChIP-seq信号相关的基因，显著富集与胁迫响应和免疫相关的注释条目，并且具有更高的序列多态性以及选择信号。本文的研究结果显示，减数分裂重组可以通过增加选择的效率，促进遗传多样性、塑造宿主-病原菌之间的共演化以及加速物种对环境的适应。