Jean Finnegan E, Kovac Kathryn A, Jaligot Estelle, Sheldon Candice C, James Peacock W, Dennis Elizabeth S
CSIRO Plant Industry, GPO Box 1600, Canberra, ACT 2601, Australia.
Plant J. 2005 Nov;44(3):420-32. doi: 10.1111/j.1365-313X.2005.02541.x.
FLOWERING LOCUS C (FLC), a repressor of flowering, is a major determinant of flowering time in Arabidopsis. FLC expression is repressed by vernalization and in plants with low levels of DNA methylation, resulting in early flowering. This repression is not associated with changes of DNA methylation within the FLC locus in either vernalized plants or plants with low levels of DNA methylation. In both cases, there is a reduction of histone H3 trimethyl-lysine 4 (K4) and acetylation of both histones H3 and H4 around the promoter-translation start of FLC. The expression of the two genes flanking FLC is also repressed in both conditions and repression is associated with decreased histone H3 acetylation. The changes in histone modifications at the FLC gene cluster, which are similar in vernalized plants and in plants with reduced DNA methylation, must arise by different mechanisms. VERNALIZATION 1, VERNALIZATION 2 and VERNALIZATION INSENSITIVE 3 modulate FLC expression in vernalized plants; these proteins play no role in the downregulation of FLC in plants with low levels of DNA methylation. Chimeric FLC::GUS transgenes respond to vernalization but these same transgenes show a position-dependent response to low levels of DNA methylation. In plants with reduced DNA methylation, expression of the five MADS AFFECTING FLOWERING (MAF) genes is repressed, suggesting that DNA methylation alters the expression of a trans-acting regulator common to FLC and members of the related MAF gene family. Our observations suggest that DNA methylation is not part of the vernalization pathway.
开花位点C（FLC）是一种开花抑制因子，是拟南芥开花时间的主要决定因素。FLC的表达在经过春化处理的植株以及DNA甲基化水平较低的植株中受到抑制，从而导致早花。无论是经过春化处理的植株还是DNA甲基化水平较低的植株，这种抑制作用都与FLC基因座内DNA甲基化的变化无关。在这两种情况下，FLC启动子 - 翻译起始位点周围的组蛋白H3三甲基赖氨酸4（K4）减少，组蛋白H3和H4的乙酰化水平也降低。在这两种情况下，FLC两侧的两个基因的表达也受到抑制，并且这种抑制与组蛋白H3乙酰化水平降低有关。FLC基因簇处组蛋白修饰的变化，在经过春化处理的植株和DNA甲基化水平降低的植株中相似，但必定是由不同机制引起的。春化1、春化2和春化不敏感3在经过春化处理的植株中调节FLC的表达；这些蛋白质在DNA甲基化水平较低的植株中对FLC的下调不起作用。嵌合的FLC::GUS转基因对春化有反应，但这些相同的转基因对低水平的DNA甲基化表现出位置依赖性反应。在DNA甲基化水平降低的植株中，五个影响开花的MADS（MAF）基因的表达受到抑制，这表明DNA甲基化改变了FLC和相关MAF基因家族成员共有的反式作用调节因子的表达。我们的观察结果表明，DNA甲基化不是春化途径的一部分。
