Schubert Daniel, Primavesi Lucia, Bishopp Anthony, Roberts Gethin, Doonan John, Jenuwein Thomas, Goodrich Justin
Institute for Molecular Plant Sciences, School of Biology, University of Edinburgh, Edinburgh, UK.
EMBO J. 2006 Oct 4;25(19):4638-49. doi: 10.1038/sj.emboj.7601311. Epub 2006 Sep 7.
The plant Polycomb-group (Pc-G) protein CURLY LEAF (CLF) is required to repress targets such as AGAMOUS (AG) and SHOOTMERISTEMLESS (STM). Using chromatin immunoprecipitation, we identify AG and STM as direct targets for CLF and show that they carry a characteristic epigenetic signature of dispersed histone H3 lysine 27 trimethylation (H3K27me3) and localised H3K27me2 methylation. H3K27 methylation is present throughout leaf development and consistent with this, CLF is required persistently to silence AG. However, CLF is not itself an epigenetic mark as it is lost during mitosis. We suggest a model in which Pc-G proteins are recruited to localised regions of targets and then mediate dispersed H3K27me3. Analysis of transgenes carrying AG regulatory sequences confirms that H3K27me3 can spread to novel sequences in a CLF-dependent manner and further shows that H3K27me3 methylation is not sufficient for silencing of targets. We suggest that the spread of H3K27me3 contributes to the mitotic heritability of Pc-G silencing, and that the loss of silencing caused by transposon insertions at plant Pc-G targets reflects impaired spreading.
植物多梳蛋白家族（Pc-G）蛋白卷曲叶（CLF）是抑制诸如AGAMOUS（AG）和无茎分生组织（STM）等靶标的必需蛋白。通过染色质免疫沉淀，我们确定AG和STM是CLF的直接靶标，并表明它们带有分散的组蛋白H3赖氨酸27三甲基化（H3K27me3）和局部H3K27me2甲基化的特征性表观遗传标记。H3K27甲基化在叶片发育过程中一直存在，与此一致的是，持续需要CLF来沉默AG。然而，CLF本身并不是一种表观遗传标记，因为它在有丝分裂过程中会丢失。我们提出了一个模型，其中Pc-G蛋白被招募到靶标的局部区域，然后介导分散的H3K27me3。对携带AG调控序列的转基因的分析证实，H3K27me3可以以CLF依赖的方式扩散到新的序列中，并进一步表明H3K27me3甲基化不足以使靶标沉默。我们认为，H3K27me3的扩散有助于Pc-G沉默的有丝分裂遗传性，并且植物Pc-G靶标处转座子插入导致的沉默丧失反映了扩散受损。
