背景回顾：The histone H3 family in animals and plants includes replicative H3 and non-replicative H3.3 variants. 

提出问题：H3.3 preferentially associates with active transcription, yet its function in development and transcription regulation remains elusive. 

研究对象：The floral transition in Arabidopsis (Arabidopsis thaliana) involves complex chromatin regulation at a central flowering repressor FLOWERING LOCUS C (FLC). 

主要研究：Here we show that H3.3 upregulates FLC expression and promotes active histone modifications Histone H3 lysine 4 trimethylation (H3K4me3) and Histone H3 lysine 36 trimethylation (H3K36me3) at the FLC locus. 

结果1-FRI介导H3.3在FLC上的富集：The FLC activator FRIGIDA (FRI) directly mediates H3.3 enrichment at FLC, leading to chromatin conformation changes and further induction of active histone modifications at FLC. 

结果2-H3.3和H2A.Z的拮抗作用：Moreover, the antagonistic H3.3 and H2A.Z act in concert to activate FLC expression, likely by forming unstable nucleosomes ideal for transcription processing. 

结果3-H3.3的敲低与功能：We also show that H3.3 knockdown leads to H3K4me3 reduction at a subset of particularly short genes, suggesting the general role of H3.3 in promoting H3K4me3. 

结果4-FLC上H3.3的沉积是活跃组蛋白修饰的先决条件：The finding that H3.3 stably accumulates at FLCin the absence of H3K36me3 indicates that the H3.3 deposition may serve as a prerequisite for active histone modifications. 

结论：Our results reveal the important function of H3.3 in mediating the active chromatin state for flowering repression.

 摘 要 

动植物中组蛋白H3家族包含与DNA复制有关的H3蛋白以及与DNA复制无关的H3.3变体。H3.3优先与活跃的转录相关，但是其在发育和转录调控方面的功能还不清楚。拟南芥的成花转变涉及主要开花抑制因子FLC基因座上复杂的染色质调控。本文中，作者发现H3.3能够上调FLC的表达，并且促进FLC位点上的组蛋白修饰H3K4me3和H3K36me3。FLC激活子FRI能够直接介导FLC位点上H3.3的富集，导致染色质构象的改变，并进一步诱导FLC基因上活跃的组蛋白修饰。此外，H3.3和H2A.Z拮抗作用于FLC基因表达的激活，而这可能是通过形成一个用于转录加工的不稳定核小体来实现的。作者还发现敲低H3.3会导致一类短基因群的H3K4me3修饰减少，说明H3.3具有促进H3K4me3的一般性功能。在没有H3K36me3的情况下，H3.3在FLC位点上的稳定累积表明H3.3沉积可能是活跃的组蛋白修饰的先决条件。本文的研究揭示了H3.3在介导开花抑制子上活跃染色质状态的重要作用。