Eukaryotic centromeres contain the kinetochore, which connects chromosomes to the spindle allowing segregation. During meiosis, centromeres are suppressed for inter-homolog crossover, as recombination in these regions can cause chromosome missegregation and aneuploidy. Plant centromeres are surrounded by transposon-dense pericentromeric heterochromatin that is epigenetically silenced by histone 3 lysine 9 dimethylation (H3K9me2), and DNA methylation in CG and non-CG sequence contexts. However, the role of these chromatin modifications in control of meiotic recombination in the pericentromeres is not fully understood. Here, we show that disruption of Arabidopsis thaliana H3K9me2 and non-CG DNA methylation pathways, for example, via mutation of the H3K9 methyltransferase genes KYP/SUVH4 SUVH5 SUVH6, or the CHG DNA methyltransferase gene CMT3, increases meiotic recombination in proximity to the centromeres. Using immunocytological detection of MLH1 foci and genotyping by sequencing of recombinant plants, we observe that H3K9me2 and non-CG DNA methylation pathway mutants show increased pericentromeric crossovers. Increased pericentromeric recombination in H3K9me2/non-CG mutants occurs in hybrid and inbred backgrounds and likely involves contributions from both the interfering and noninterfering crossover repair pathways. We also show that meiotic DNA double-strand breaks (DSBs) increase in H3K9me2/non-CG mutants within the pericentromeres, via purification and sequencing of SPO11-1-oligonucleotides. Therefore, H3K9me2 and non-CG DNA methylation exert a repressive effect on both meiotic DSB and crossover formation in plant pericentromeric heterochromatin. Our results may account for selection of enhancer trap Dissociation (Ds) transposons into the CMT3 gene by recombination with proximal transposon launch-pads.

中文翻译：

---

通过丧失 H3K9me2 和非 CG DNA 甲基化，拟南芥着丝粒附近减数分裂重组的表观遗传激活。

真核生物的着丝粒包含着丝粒，它将染色体连接到纺锤体以允许分离。在减数分裂过程中，着丝粒因同系物间交叉而受到抑制，因为这些区域的重组会导致染色体错误分离和非整倍体。植物着丝粒被转座子致密的着丝粒周围异染色质包围，该异染色质被组蛋白 3 赖氨酸 9 二甲基化 (H3K9me2) 和 CG 和非 CG 序列背景中的 DNA 甲基化表观遗传沉默。然而，这些染色质修饰在控制着丝粒周围减数分裂重组中的作用尚不完全清楚。在这里，我们展示了拟南芥 H3K9me2 和非 CG DNA 甲基化途径的破坏，例如，通过 H3K9 甲基转移酶基因 KYP/SUVH4 SUVH5 SUVH6 或 CHG DNA 甲基转移酶基因 CMT3 的突变，增加着丝粒附近的减数分裂重组。使用 MLH1 病灶的免疫细胞学检测和重组植物测序的基因分型，我们观察到 H3K9me2 和非 CG DNA 甲基化途径突变体显示着丝粒周围交叉增加。H3K9me2/非 CG 突变体中着丝粒周围重组的增加发生在杂交和近交系背景中，并且可能涉及干扰和非干扰交叉修复途径的贡献。我们还表明，通过 SPO11-1-寡核苷酸的纯化和测序，减数分裂 DNA 双链断裂 (DSB) 在着丝粒周围的 H3K9me2/非 CG 突变体中增加。因此，H3K9me2 和非 CG DNA 甲基化对植物着丝粒周围异染色质中的减数分裂 DSB 和交叉形成均有抑制作用。