RESEARCH-PGR: Zygotic Genome Activation in Rice

母本配子和父本配子的融合形成受精卵，它标志着从单个细胞开始形成新的植物。这是植物生命周期的关键阶段。伴随着受精卵的发育，通过DNA和相关蛋白质的化学修饰对基因表达模式进行广泛的重新编程，也称为表观遗传过程。以前的研究表明，植物合子基因的大规模激活发生得比动物更早；然而，母本和父本遗传物质对合子基因激活的时间和相对贡献都没有很好的定义。此外，由于在早期发育的精确时间点分离单细胞受精卵存在困难，在开花植物中还没有对合子基因组最早阶段的重新编程和激活进行详细的表征。这个项目将描述由表观遗传机制在水稻受精卵中介导的全基因组变化，水稻是一种重要的农作物。这项研究将从受精开始讨论受精卵发育的早期阶段，并将利用单细胞分离和分子分析方面的最新技术进步。了解配子形成受精卵对于提高种子产量、从组织培养中再生植物以及改进杂交育种方法具有农业应用价值。该项目还将为兰斯顿大学的学生和教职员工提供植物生物学和基因组学方面的培训。兰斯顿大学是俄克拉荷马州历史上的一所非裔美国人机构。大米是研究受精卵基因组激活过程中基因组重新编程相关机制的极好模型。水稻是开花植物中从授粉到受精时间最短的植物之一，这一特点使得分离精确阶段的受精卵用于分析是可行的。合子基因组激活的表观遗传过程将通过鉴定雄配子和雌配子的小RNA转录体和甲基组，以及来自自花授粉和杂交组合的受精卵来阐明。这些目标包括识别针对母体转录本的微型RNA，针对转座子的沉默的短干扰RNA，以及参与合子染色质重置的潜在的新的小RNA。具有单亲合子表达的基因座将被调查甲基化标记的传递或擦除。该分析将纳入影响依赖于RNA的甲基化途径的突变。这些数据集将被用来生成胚胎发育中亲本表达的模型，以及通过生殖系沉默转座元件和建立结构性异染色域的模型。项目成果将导致弥合在了解植物生命周期的根本转变方面的主要差距。

Fusion of the maternal and paternal gametes forms the zygote, and it marks the initiation of a new plant from a single cell. This is a critical stage in the life cycle of the plant. Extensive reprogramming of the pattern of gene expression through chemical modifications of DNA and associated proteins, also known as epigenetic processes, accompany zygote development. Previous studies have shown that the large-scale activation of plant zygotic genes occurs earlier than it does in animals; however, both the timing and the relative contributions of the maternal and paternal genetic material to zygotic gene activation are not well defined. Furthermore, a detailed characterization of the reprogramming and activation of the zygotic genome at the earliest stages has not been performed in a flowering plant due to the difficulties in isolating single-cell zygotes at precise time points during early development. This project will characterize genome-wide changes mediated by epigenetic mechanisms in zygotes from rice, an important crop plant. This study will address the early stages of zygote development starting at fertilization, and will utilize the latest technical advances in the isolation and molecular analysis of single cells. Understanding the formation of zygotes from gametes has agricultural applications for increased seed yields, for regeneration of plants from tissue culture, and for improved methods of breeding hybrids. The project will also provide training in plant biology and genomics to students and faculty from Langston University, a historically African-American institution in Oklahoma.Rice is an excellent model to study the mechanisms associated with genome reprograming during zygote genome activation. Rice has one of the shortest time from pollination to fertilization among flowering plants, a characteristic that makes feasible the isolation of precisely-staged zygotes for analysis. Epigenetic processes in zygotic genome activation will be elucidated by characterization of the small RNA transcriptomes and methylomes of the male and female gametes, and of zygotes derived from self-pollinated as well as hybrid crosses. The aims include identification of micro RNAs targeting maternal transcripts, short interfering RNAs targeting transposons for silencing, and potentially novel small RNAs involved in zygotic chromatin resetting. Loci with uniparental zygotic expression will be investigated for transmission or erasure of methylation marks. The analysis will incorporate mutants affecting RNA-dependent methylation pathways. The datasets will be used to generate models for parent-of-origin expression in embryogenesis, as well as for silencing of transposable elements and establishment of constitutive heterochromatic domains through the germline. The project outcomes will result in the closure of major gaps in the understanding of a fundamental transition in the life cycle of plants.