Epigenetic regulation of developmental phase transition

多梳抑制复合体2 （polycomb repression complex 2, PRC2）是基因表达和发育的重要调控因子。PRC2蛋白在真菌、蠕虫、苍蝇、哺乳动物和许多植物物种中都是保守的。在模式植物拟南芥中，PRC2控制着胚乳的发育，胚乳是种子中为胚胎提供营养的组织。在单子房植物中，如玉米，胚乳构成了成熟种子的主要部分，并构成了可食用果仁的大部分。由于胚乳是种子的主要组成部分，因此了解胚乳的发育对农业具有重要意义。在许多薯类植物中，胚乳增殖是成熟种子大小的主要决定因素，这在拟南芥和相关作物油菜中已经得到证实。胚乳的增殖为随后的胚胎发育提供营养。该奖项的目的是更好地了解PRC2如何调节胚乳形成。该项目增强了国家科学基金会的研究和教育使命。处于职业发展不同阶段的研究人员接受遗传学、分子生物学和生物化学领域的培训。学生和学员在职业发展、教学、沟通和人际交往技巧以及专业发展等方面得到指导。积极的外联活动促进科学素养和公众对科学的参与。在被子植物中，双受精导致二倍体胚胎和三倍体胚乳的形成。在许多双子叶植物中，种子发育包括早期胚乳增殖形成一个大胚囊，然后是第二阶段，胚胎生长以在成熟时取代大部分胚乳。一些对胚乳增殖至关重要的基因如MINI3和IKU2的表达在受精后被激活。授粉后4天，胚乳增殖基因被抑制，向胚胎发育过渡。PRC2s在发育相变中起着重要作用。在三个PRC2复合物中，受精独立种子(FIS)-PRC2通过组蛋白甲基化沉默胚乳增殖基因。没有一个PRC2亚基以序列特异性的方式结合DNA，而且关于PRC2如何被招募到特定基因组位点的知识是有限的。MEA是FIS-PRC2复合体的组蛋白甲基转移酶，并积累4dap。与MEA积累平行，两个AGAMOUS-LIKE (AGL) MADS-box基因在DAP中活跃转录。这两种AGL蛋白结合IKU2启动子并与MEA相互作用。因此，MEA的动态积累调节了胚乳增殖的持续时间，这两个agl是将MEA组蛋白写入者招募到IKU2等潜在位点的读者。它们的共同作用促进了胚胎发育的阶段转变。在这个项目中，我们将探索与IKU2位点组蛋白修饰相关的MEA的动态积累，以及MEA在IKU2和其他位点的招募。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The polycomb repressive complex 2 (PRC2) is an important regulator of gene expression and development. PRC2 proteins are conserved in fungi, worm, fly, mammals and many plant species. In the model plant, Arabidopsis thaliana, PRC2 controls the development of the endosperm, the tissue in the seed that provides nutrients for the embryo. In monocots, like maize the endosperm constitutes the major volume of mature seeds and it the bulk of the edible kernel. Because the endosperm is a major constituent of seeds, an understanding of endosperm development has critical implications for agriculture. In many dicots, endosperm proliferation is the major determinant of mature seed size as has been shown in Arabidopsis thaliana and the related crop plant, canola. Endosperm proliferation in these dicots provides nutrient supplies for the subsequent embryo development. The aim of this award is to better understand how PRC2 regulates endosperm formation. This project augments the research and education missions of NSF. Researchers at different stages of their career development are trained in the fields of genetics, molecular biology and biochemistry. Students and trainees are mentored in the areas of career development, teaching, communication and interpersonal skills and professional development. Vigorous outreach activities foster scientific literacy and public engagement with science.In angiosperms, double fertilization leads to the formation of a diploid embryo and a triploid endosperm. In many dicots, seed development involves an early endosperm proliferation to form a large embryo sac followed by a second phase in which the embryo grows to replace most of the endosperm at maturity. The expression of a few genes critical for endosperm proliferation such as MINI3 and IKU2 is activated after fertilization. At 4 days after pollination (DAP), the endosperm proliferation genes are repressed for a transition to embryo development. PRC2s play important roles in developmental phase transition. Of the three PRC2 complexes, Fertilization Independent Seed (FIS)-PRC2 silences the endosperm proliferation genes through histone methylation. None of the PRC2 subunits bind DNA in a sequence-specific fashion, and the knowledge of how PRC2s are recruited to a particular genomic locus is limited. MEA is the histone methyltransferase of the FIS-PRC2 complex and accumulates 4 DAP. Parallel to MEA accumulation, two AGAMOUS-LIKE (AGL) MADS-box genes are actively transcribed 4 DAP. The two AGL proteins bind the IKU2 promoter and interact with MEA. Therefore, the dynamic accumulation of MEA regulates the duration of endosperm proliferation, and the two AGLs are the readers to recruit MEA histone writer to the IKU2 and other potential loci. Their co-action facilitates a phase transition to embryo development. In this project, the dynamic MEA accumulation in relation to histone modification at the IKU2 locus and the recruitment of MEA to the IKU2 and other loci is explored.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.