Flowering is a key developmental transition in the plant life cycle. In temperate climates, flowering often occurs in response to the perception of seasonal cues such as changes in day-length and temperature. However, the mechanisms that have evolved to control the timing of flowering in temperate grasses are not fully understood. We identified a Brachypodium distachyon mutant whose flowering is delayed under inductive long-day conditions due to a mutation in the JMJ1 gene, which encodes a Jumonji domain-containing protein. JMJ1 is a histone demethylase that mainly demethylates H3K4me2 and H3K4me3 in vitro and in vivo. Analysis of the genome-wide distribution of H3K4me1, H3K4me2, and H3K4me3 in wild-type plants by chromatin immunoprecipitation and sequencing (ChIP-seq) combined with RNA sequencing (RNA-seq) revealed that H3K4m1 and H3K4me3 are positively associated with gene transcript levels, whereas H3K4me2 is negatively correlated with transcript levels. Furthermore, JMJ1 directly binds to the chromatin of the flowering regulator genes VRN1 and ID1 and affects their transcription by modifying their H3K4me2 and H3K4me3 levels. Genetic analyses indicated that JMJ1 promotes flowering by activating VRN1 expression. Our study reveals a role for JMJ1-mediated chromatin modification in the proper timing of flowering in B. distachyon.

中文翻译：

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二穗短柄草的正确开花时间需要 H3K4 去甲基酶 JMJ1

开花是植物生命周期中的关键发育转变。在温带气候下，开花通常是根据对季节线索的感知而发生的，例如白昼长度和温度的变化。然而，控制温带草类开花时间的进化机制尚不完全清楚。我们鉴定了一种短柄草突变体，其开花在诱导长日照条件下延迟，这是由于 JMJ1 基因（编码包含 Jumonji 结构域的蛋白质）的突变所致。 JMJ1是一种组蛋白去甲基化酶，主要在体外和体内使H3K4me2和H3K4me3去甲基化。通过染色质免疫沉淀和测序（ChIP-seq）结合RNA测序（RNA-seq）分析野生型植物中H3K4me1、H3K4me2和H3K4me3的全基因组分布，结果表明H3K4m1和H3K4me3与基因转录水平正相关，而 H3K4me2 与转录水平呈负相关。此外，JMJ1 直接与开花调节基因 VRN1 和 ID1 的染色质结合，并通过修改 H3K4me2 和 H3K4me3 水平来影响它们的转录。遗传分析表明，JMJ1 通过激活 VRN1 表达来促进开花。我们的研究揭示了 JMJ1 介导的染色质修饰在二穗花的正确开花时间中的作用。