植物春化起始的分子机制及新作用因子挖掘

For winter annual plants, the exposure to a prolonged cold is essential to flower in the spring. This process is called as vernalization, which involves the traditional epigenetic gene silencing mechanism. In Arabidopsis, the main target of vernalization is the FLC gene, and the silencing mechanism requires the long non-coding RNAs (lncRNAs) COOLAIR and COLDAIR, and the Polycomb Repressive Complex PHD-PRC2 for quantitatively decreasing of H3K36me3 and increasing of H3K27me3 levels. It has been reported that the earliest events for proper vernalization initiation are the reduction of H3K36me3 level and the induction of COOLAIR RNA expression. However, the regulatory mechanism for vernalization initiation, like how the H3K36me3 demethylation process regulated, have not been investigated. This project will: 1) analyze the H3K36me3 methyltransferases activities during vernalization initiation; 2) identify the H3K36me3 demethylases that function in vernalization initiation; and 3) how lncRNA COOLAIR involved in initiation of vernalization. Results obtained from this project will reveal the mechanism of vernalization initiation and identify new components involved in this process. I believe that this project will achieve a significant progress and breakthrough in plant epigenetics like histone modifications regulation and lncRNA functions; and may guide for better crop production.

春化是促进冬性植物开花的重要途径，在拟南芥中春化可导致FLC基因发生沉默。目前已知这一过程需要多种成分参与，包括长链非编码RNA COOLAIR、 COLDAIR以及多梳族蛋白复合体PHD-PRC2等。它们通过调节H3K36me3和H3K27me3修饰水平发挥作用。已知春化过程中最早发生的事件包括H3K36me3修饰水平下降和COOLAIR表达水平上调，但启动春化的具体调控机理尚不清楚。本项目将通过分析1）组蛋白H3K36me3甲基转移酶活性在春化早期是否被抑制；2）寻找在春化早期发挥作用的H3K36me3去甲基化酶；和3）COOLAIR如何协助春化早期H3K36me3去甲基化过程来控制FLC基因的沉默等三方面来解析春化早期H3K36me3去甲基化的发生机制并寻找这一过程中新的作用因子。实施本项目将在植物表观遗传学包括组蛋白修饰和长链非编码RNA调控机理方面产生新理论，并可望指导农业生产。

模式植物拟南芥的春化途径通过低温稳定抑制FLC基因表达从而促进开花。在该项目的支持下，本组发现内含子中的转座子在调控宿主基因FLC表达以及春化起始过程中发挥重要功能，并取得以下重要研究成果：1）通过正向遗传筛选，我们发现RNA聚合酶VI和V对维持FLC正常表达至关重要；2）在RNA聚合酶VI和V功能缺失的突变体中，内含子中的转座子介导的非正常转录起始导致产生非正常的FLCTE转录本；3）RNA聚合酶VI和V通过在内含子中建立DNA甲基化和H3K9二甲基化来抑制转座子介导的非正常转录起始；4）我们发现RNA介导的DNA甲基化途径（RdDM pathway）抑制内含子转座子介导的非正常转录起始这个机制在拟南芥基因组普遍存在；5）维持FLC内含子中的转座子异染色质状态使得植物正常响应春化，以及低温春化可以抑制FLCTE转录本产生。这些结果表明，内含子转座子可以通过调控基因的转录起始来影响植物对春化的响应，拓展了学界对植物春化起始机制的认识。

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