Epigenetic activation of meiotic recombination near Arabidopsis thaliana centromeres via loss of H3K9me2 and non-CG DNA methylation

First author: Charles J. Underwood; Affiliations: Cold Spring Harbor Laboratory (冷泉港实验室): Fort Collins, USA

Corresponding author: Robert A. Martienssen

Eukaryotic centromeres (着丝粒) contain the kinetochore (着丝点), which connects chromosomes to the spindle (纺锤体) allowing segregation. During meiosis (减数分裂), centromeres are suppressed for inter-homolog crossover (交换), as recombination in these regions can cause chromosome missegregation (染色体错分) and aneuploidy (非整倍性). Plant centromeres are surrounded by transposon-dense pericentromeric heterochromatin (近着丝粒异染色质) 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 (近着丝粒区) 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 (H3K9甲基转移酶基因) KYP/SUVH4 SUVH5 SUVH6, or the CHG DNA methyltransferase gene CMT3, increases meiotic recombination in proximity to (接近) the centromeres. Using immunocytological detection (免疫细胞化学检测) of MLH1 foci and genotyping by sequencing (通过测序基因分型) 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 (寡核苷酸). 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.

真核生物的着丝粒包含一个着丝点，能够牵引染色体到纺锤体上实现分离。在减数分裂时，着丝点同源染色体间的交换会被抑制，在这些区域的重组会引起染色体的错分和非整倍性。植物着丝粒周围聚集了转座子密集的近着丝粒异染色质，受H3K9me2、CG和非CG序列的DNA甲基化的表观抑制。然而，这些染色质修饰在近着丝粒区减数分裂重组中发挥的调控作用了解的很少。本文报道了通过突变拟南芥H3K9甲基转移酶基因KYP/SUVH4 SUVH5 SUVH6或是CHG DNA甲基转移酶基因CMT3导致的H3K9me2和non-CG DNA甲基化通路破环能够增加着丝粒附近的减数分裂重组。利用MLH1位点的免疫细胞化学检测和对重组植株的基于测序的基因分型，作者观测到了H3K9me2和非CG DNA甲基化通路突变体表现出了近着丝粒区交换的增加。在H3K9me2/non-CG突变杂交或是自交系中，近着丝粒区的重组增加，可能涉及到干扰和非干扰交换修复通路。另外，通过对SPO11-1-寡核苷酸的纯化和测序，显示在H3K9me2/non-CG突变体的近着丝粒区减数分裂DNA双链断裂DSB增加。因此，H3K9me2和non-CG DNA甲基化对于植物近着丝粒异染色质区的减数分裂DSB和交换的形成均有抑制作用。

通讯：Robert A. Martienssen (https://www.cshl.edu/research/faculty-staff/rob-martienssen/)

研究方向：植物与裂殖酵母中的表观遗传

doi: 10.1101/gr.227116.117

Journal: Genome Research

Published online: 12 March, 2018

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