DISSERTATION RESEARCH: Evolution of Angiosperm Seed Development: perspectives from Nymphaea thermarum (Nymphaeales)

开花植物的种子具有一种新的组织——胚乳。胚乳是第二次受精事件的产物，但它不是发育成第二个胚胎，而是成为一个组织，调解母系植物与其同胞胚胎之间的关系。胚乳也是人类饮食的重要组成部分：提供人们消耗的大部分卡路里的种子（大米、小麦、玉米）主要由胚乳组成。模式植物物种的研究已经开始拼凑出控制胚乳发育的机制，并揭示了基因印记在胚乳发育中起着重要作用。当从父母一方遗传的等位基因沉默时，就会发生印记。很少有人关注开花植物的印记是如何进化的。该项目将通过分析睡莲胚乳发育过程中的基因表达来解决这一差异，睡莲是开花植物中最古老的谱系之一。虽然睡莲独特地适合成为早期分化谱系的模型系统，但它也处于灭绝的边缘——这使得它成为一个令人信服的案例，说明为什么探索和保护生物多样性对进一步的基础科学研究至关重要。基因表达分析将通过创建胚珠和种子发育关键阶段的RNA-seq转录组来完成。从这个数据集中，两大类基因将成为同源鉴定的目标：参与印迹调节机制的基因和自身印迹的基因。这些同源基因的存在或缺失将有助于解决在被子植物进化过程中这些机制何时成为胚乳发育的重要调控机制的问题。此外，采样方案将使区分与特定发育过程相关的基因活动套件成为可能。最后，随附的序列和表达数据将用于重建相关基因家族的进化史。该数据库将成为了解被子植物种子进化的重要资源，并将向公众开放。

Seeds of flowering plants are distinguished by the presence of a novel tissue - endosperm. Endosperm is the product of a second fertilization event, but rather than developing into a second embryo, it becomes a tissue that mediates the relationship between the maternal plant and its compatriot embryo. Endosperm is also an essential part of the human diet: the seeds that provide most of the calories people consume (rice, wheat, corn) consist primarily of endosperm. Studies in model plant species have begun to piece together the mechanisms that control endosperm development, and have revealed that gene imprinting plays an important role. Imprinting occurs when an allele inherited from one parent is silenced. Little scientific attention has been given to how imprinting has evolved in flowering plants. This project will address this discrepancy by analyzing the expression of genes during development of endosperm in the water lily, which is a member of one of the most ancient lineages of flowering plants. While the water lily is uniquely suited to become a model system for the early diverging lineages, it is also on the brink of extinction - making it a compelling case for why exploring and preserving biodiversity is essential for furthering basic scientific research. Analysis of gene expression will be accomplished by creating RNA-seq transcriptomes of key stages during ovule and seed development. From this dataset, two main categories of genes will be targeted for homolog identification: genes that are involved in imprinting-regulation mechanisms and genes that are themselves imprinted. Simple presence/absence of homologs of these genes during seed development in N. thermarum will help to resolve the question of when during angiosperm evolution did these mechanisms became important regulators of endosperm development. In addition, the sampling scheme will make it possible to distinguish suites of gene activity that correlate to specific sets of developmental processes. Finally, the accompanying sequence and expression data will be used to reconstruct the evolutionary history of relevant gene families. This database will represent an important resource for understanding the evolution of angiosperm seeds, and will be made publically available.