背景回顾：It is challenging to determine the effect of DNA methylation on the epigenetic landscape and the function in higher organisms due to the lack of DNA methylation-free mutants. 

主要发现：Here, the analysis of a recently generated Arabidopsis mutant completely devoid of DNA methylation reveals that DNA methylation underpins the genome-wide landscape of histone modifications. 

结果1-DNA甲基化与组蛋白修饰：Complete loss of DNA methylation causes an upheaval of the histone modification landscape, including complete loss of H3K9me2 and widespread redistribution of active and H3K27me3 histone marks, mostly owing to the role of DNA methylation in initiating H3K9me2 deposition and excluding active marks and repressive mark H3K27me3; CG and non-CG methylation can act independently at some genomic regions while they act cooperatively at many other regions. 

结果2-DNA甲基化与转录控制：The transcriptional reprogramming upon loss of all DNA methylation correlates with the extensive redistribution or switches of the examined histone modifications. Histone modifications retained or gained in the DNA methylation-free mutant serve as DNA methylation-independent transcriptional regulatory signals: active marks promote genome transcription, whereas the repressive mark H3K27me3 compensates for the lack of DNA hypermethylation/H3K9me2 at multiple transposon families. 

结论：Our results show that an intact DNA methylome constitutes the scaffolding of the epigenomic landscape in Arabidopsis and is critical for controlled genome transcription and ultimately for proper growth and development.

Function of DNA methylation in histone modification and transcription landscapes.

由于缺乏不含DNA甲基化的突变体，很难明确DNA甲基化对表观的影响及其在高等生物中的功能。本文中，通过分析一个最近获得的完全没有DNA甲基化的拟南芥突变体，作者发现DNA甲基化支撑着全基因组范围上的组蛋白修饰。完全缺失DNA甲基化会导致全基因组蛋白修饰的剧烈变化，包括H3K9me2的缺失以及激活性组蛋白标记和H3K27me3组蛋白标记的重分布，主要是由于DNA甲基化作用于H3K9me2沉积的起始、激活性组蛋白标记和抑制性标记H3K27me3的排除；CG和非CG甲基化在大多数基因组位点上都是协同作用的，但也可以独立于作用于某些基因组位点。所有DNA甲基化丢失后的转录重编程与测试组蛋白修饰的广泛重分布或转变有关。无DNA甲基化突变体中保留或新获得的组蛋白修饰作为独立于DNA甲基化的转录调控信号发挥作用，激活性标记促进基因组转录，而抑制性标记H3K27me3则弥补了多个转座子家族上DNA超甲基化/H3K9me2的丢失。本文的研究结果显示，一个完整的DNA甲基化组构成了拟南芥表观组的基础性架构，对于控制基因组转录以及与之关联的正常生长和发育至关重要。

** 朱健康 **