Maize Unstable factor for orange1 Is Required for Maintaining Silencing Associated with Paramutation at the pericarp color1 and booster1 Loci
Maize Unstable factor for orange1 Is Required for Maintaining Silencing Associated with Paramutation at the pericarp color1 and booster1 Loci
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DOI：
10.1371/journal.pgen.1002980
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发表时间：
2012-10-01
期刊：
影响因子：
4.5
通讯作者：
Chopra, Surinder
中科院分区：
文献类型：
--
作者：
Sekhon, Rajandeep S.;Wang, Po-Hao;Chopra, Surinder
为了了解副突变的分子机制，我们研究了橙色不稳定因子1（Ufo 1）在维持玉米果皮颜色1（p1）和助推器1（b1）基因座副突变中的作用。遗传测试显示，Ufo 1 -1突变破坏了与p1和b1处的副突变相关的沉默。在b1达到的上调水平低于在p1，这表明Ufo 1 -1在这些位点发挥的作用的差异。我们研究了Ufo 1 -1与两个沉默的p1表观等位基因P1-rr'和P1-pr（TP）的相互作用，这两个表观等位基因来自一个共同的P1-rr祖先。两个等位基因在表型上是不可区分的，但在它们的副诱变活性上不同; P1-rr'对P1-rr是副诱变的，而P1-pr（TP）是非副诱变的。胞嘧啶甲基化分析揭示了副突变所需的增强子片段内的显着差异; P1-rr'在对称（CG和CHG）和不对称（CHH）位点表现出甲基化增加，而P1-pr（TP）仅在对称位点发生甲基化。这两个沉默的等位基因有较高水平的二甲基化赖氨酸9组蛋白3（H3 K9 me 2），沉默染色质的表观遗传标记，在增强子区域。两个表观等位基因在Ufo 1 -1背景下被重新激活;然而，P1-rr'的重新激活与增强子中对称和不对称胞嘧啶甲基化的显著丧失相关，而上调的P1-pr（TP）的甲基化不受影响。有趣的是，Ufo 1 -1介导的两个等位基因的再激活伴随着增强子区域的H3 K9 me 2标记的丢失。因此，虽然早期的研究表明H3 K9 me 2和DNA甲基化之间的相关性，我们的研究表明，这两个表观遗传标记在Ufo 1 -1-重新激活的p1等位基因中是不偶联的。此外，虽然CHH甲基化在增强子区域似乎是主要的区别标记之间的副突变和非副突变的p1等位基因，H3 K9 me 2标记似乎是重要的维持表观遗传沉默。
To understand the molecular mechanisms underlying paramutation, we examined the role of Unstable factor for orange1 (Ufo1) in maintaining paramutation at the maize pericarp color1 (p1) and booster1 (b1) loci. Genetic tests revealed that the Ufo1-1 mutation disrupted silencing associated with paramutation at both p1 and b1. The level of up regulation achieved at b1 was lower than that at p1, suggesting differences in the role Ufo1-1 plays at these loci. We characterized the interaction of Ufo1-1 with two silenced p1 epialleles, P1-rr' and P1-pr(TP), that were derived from a common P1-rr ancestor. Both alleles are phenotypically indistinguishable, but differ in their paramutagenic activity; P1-rr' is paramutagenic to P1-rr, while P1-pr(TP) is non-paramutagenic. Analysis of cytosine methylation revealed striking differences within an enhancer fragment that is required for paramutation; P1-rr' exhibited increased methylation at symmetric (CG and CHG) and asymmetric (CHH) sites, while P1-pr(TP) was methylated only at symmetric sites. Both silenced alleles had higher levels of dimethylation of lysine 9 on histone 3 (H3K9me2), an epigenetic mark of silent chromatin, in the enhancer region. Both epialleles were reactivated in the Ufo1-1 background; however, reactivation of P1-rr' was associated with dramatic loss of symmetric and asymmetric cytosine methylation in the enhancer, while methylation of up-regulated P1-pr(TP) was not affected. Interestingly, Ufo1-1-mediated reactivation of both alleles was accompanied with loss of H3K9me2 mark from the enhancer region. Therefore, while earlier studies have shown correlation between H3K9me2 and DNA methylation, our study shows that these two epigenetic marks are uncoupled in the Ufo1-1-reactivated p1 alleles. Furthermore, while CHH methylation at the enhancer region appears to be the major distinguishing mark between paramutagenic and non-paramutagenic p1 alleles, H3K9me2 mark appears to be important for maintaining epigenetic silencing.