Epigenetic regulation of sexual lineage development in plants

生命的一个关键特征是繁殖的能力。繁殖策略是进化适合度的主要贡献者，在不同物种之间可以有很大的差异。像人类一样，大多数开花植物通过与另一个个体交配进行有性繁殖；然而，与人类不同的是，植物通常同时拥有雄性和雌性器官，许多植物物种，包括主要作物，都能够自交。开花植物的有性繁殖对人类很重要，因为它产生了构成我们大部分主食的种子。随着耕地的减少、人口的爆炸性增长和全球气候变化，在21世纪养活世界将需要种子生产效率的阶段性变化，而这只能来自对植物生殖发展的更深入了解。植物中的有性繁殖是由两个高度专业化的细胞家族进行的，这里称为雄性和雌性有性系(SLS)。一个基本但仍未解决的问题一直让我着迷，那就是SL的功能和命运是如何在这些细胞谱系中准确地安装和维持的。我的DPhil和博士后研究重点是遗传和‘表观遗传’途径如何影响SL功能和生育能力。表观遗传调控--例如DNA甲基化--是因为它能够通过改变DNA的状态而不改变其遗传序列来改变基因的表达。最近，我发现RNA引导的DNA甲基化(RdDM)途径通过控制数百个基因的表达来调控拟南芥植物SL的发育。与RdDM途径在SL发育中的重要性一致，它的突变导致了拟南芥和玉米SL发育的缺陷。本研究结合植物发育、分子、遗传学和表观遗传学生物学，研究RdDM如何在模式植物拟南芥的雄性SL中建立生殖功能和命运。为了检测DNA甲基化和基因表达的变化，我开发了最先进的技术，如荧光激活细胞分选和显微操作，以分离所有类型的男性SL细胞以获得高纯度。我将使用这些来自RdDM突变体的SL细胞的全基因组测序来精确定位SL特定的RdDM途径的功能，并结合遗传学和发育生物学来确定由SL特定的RdDM控制的基因如何调控SL的发育。最后，通过基因组学、发育生物学和突变筛选的组合，我将破译RdDM与SL中的基因有关的机制。这个多学科的工作计划将通过识别一些关键的遗传和表观遗传调节因子来加深我们对男性SL发育和功能的理解。由于雄性和雌性SL发育有显著的相似之处，而且在模式植物拟南芥中的发现已经被常规地转化为主要作物，如水稻和玉米，这些见解将被广泛应用，并可能用于提高作物的肥力和产量。在更一般的层面上，我的工作将第一次展示，如何在特定的细胞谱系中定制表观遗传途径，以传递精确的生物功能。这种发育调节可能会影响多种细胞类型和组织中的许多生物学过程。因此，我相信我的工作将为研究植物发育的表观遗传调控奠定基础。许多DNA甲基化机制在拟南芥和哺乳动物之间是高度保守的，最近的证据表明DNA甲基化在指导人类细胞系的分化中发挥了作用。因此，这项工作的见解有可能阐明哺乳动物中DNA甲基化对谱系发育的调节，这对于抗击与DNA甲基化相关的人类疾病，如癌症，是重要的。

A key characteristic of life is the ability to reproduce. Reproductive strategies are major contributors to evolutionary fitness and can vary substantially between species. Like humans, most flowering plants reproduce sexually by mating with another individual; however, unlike humans, plants typically possess both male and female organs, and many plant species, including major crops, are capable of self-fertilization. Sexual reproduction in flowering plants is important to mankind as it produces the seeds that comprise most of our staple food. With decreasing arable land, an exploding population and global climate change, feeding the world in the 21st century will require a step-change in the efficiency of seed production, and this can only come from a deeper understanding of plant reproductive development. Sexual reproduction in plants is carried out by two highly specialized families of cells, here called the male and female sexual lineages (SLs). A fundamental but still unresolved question that has always fascinated me is how SL function and fate are installed and maintained precisely in these cell lineages. My DPhil and postdoctoral studies focused on how genetic and 'epigenetic' pathways contribute to SL function and fertility. 'Epigenetic' regulation - such as DNA methylation - is named after its ability to alter gene expression by modifying the state of DNA without changing its genetic sequence. Recently, I discovered that the RNA-directed DNA methylation (RdDM) pathway regulates SL development in Arabidopsis plants by controlling the expression of several hundred genes. Consistent with the importance of the RdDM pathway in SL development, its mutations cause defects in SL development in both Arabidopsis and maize. My proposed research integrates plant developmental, molecular, genetics and epigenetics biology to investigate how RdDM installs reproductive function and fate in the male SL of the model plant Arabidopsis thaliana. To detect changes in the DNA methylation and gene expression, I have developed state-of-the-art techniques such as fluorescence-activated cell sorting and micromanipulation to isolate all types of male SL cells to high purity. I will use whole-genome sequencing of these SL cells from RdDM mutants to pinpoint the function of the SL-specific RdDM pathway, and a combination of genetics and developmental biology to determine how the genes controlled by the SL-specific RdDM regulate SL development. Finally, through a combination of genomics, developmental biology and mutant screens, I will decipher the mechanism by which RdDM is directed to genes in the SL.This multi-disciplinary program of work will deepen our understanding of male SL development and function by identifying a number of key genetic and epigenetic regulators. Due to the significant parallels between male and female SL development, and because discoveries in the model plant Arabidopsis have been routinely translated into major crops such as rice and maize, these insights will be widely applicable and may be used to improve crop fertility and yield. At a more generic level, my work will demonstrate, for the first time, how epigenetic pathways can be tailored in a specific lineage of cells to convey precise biological functions. This kind of developmental regulation likely affects many biological processes in a wide range of cell types and tissues. I therefore believe that my work will lay a foundation for the study of epigenetic regulation of plant development. Many DNA methylation mechanisms are highly conserved between Arabidopsis and mammals, and recent evidence points to a role for DNA methylation in directing the differentiation of human cell lines. Insights from this work thus have the potential to shed light on the regulation of lineage development by DNA methylation in mammals, which is important to combat DNA methylation-related human diseases such as cancer.