Bastow Ruth, Mylne Joshua S, Lister Clare, Lippman Zachary, Martienssen Robert A, Dean Caroline
Department of Cell and Developmental Biology, John Innes Centre, Norwich Research Park, Colney, Norwich NR4 7UH, UK.
Nature. 2004 Jan 8;427(6970):164-7. doi: 10.1038/nature02269.
To ensure flowering in favourable conditions, many plants flower only after an extended period of cold, namely winter. In Arabidopsis, the acceleration of flowering by prolonged cold, a process called vernalization, involves downregulation of the protein FLC, which would otherwise prevent flowering. This lowered FLC expression is maintained through subsequent development by the activity of VERNALIZATION (VRN) genes. VRN1 encodes a DNA-binding protein whereas VRN2 encodes a homologue of one of the Polycomb group proteins, which maintain the silencing of genes during animal development. Here we show that vernalization causes changes in histone methylation in discrete domains within the FLC locus, increasing dimethylation of lysines 9 and 27 on histone H3. Such modifications identify silenced chromatin states in Drosophila and human cells. Dimethylation of H3 K27 was lost only in vrn2 mutants, but dimethylation of H3 K9 was absent from both vrn1 and vrn2, consistent with VRN1 functioning downstream of VRN2. The epigenetic memory of winter is thus mediated by a 'histone code' that specifies a silent chromatin state conserved between animals and plants.
为确保在适宜条件下开花，许多植物只有在经历一段较长的寒冷期（即冬季）后才会开花。在拟南芥中，长时间的寒冷加速开花，这一过程称为春化作用，涉及到蛋白质FLC的下调，否则FLC会阻止开花。通过VERNALIZATION（VRN）基因的活性，这种降低的FLC表达在后续发育过程中得以维持。VRN1编码一种DNA结合蛋白，而VRN2编码一种多梳蛋白家族蛋白的同源物，该蛋白在动物发育过程中维持基因沉默。我们在此表明，春化作用会导致FLC基因座内离散区域的组蛋白甲基化发生变化，增加组蛋白H3赖氨酸9和27的二甲基化。这种修饰在果蝇和人类细胞中可识别沉默染色质状态。仅在vrn2突变体中H3 K27的二甲基化缺失，但vrn1和vrn2中H3 K9的二甲基化均不存在，这与VRN1在VRN2下游发挥作用一致。因此，冬季的表观遗传记忆是由一种“组蛋白密码”介导的，该密码指定了动植物之间保守的沉默染色质状态。
