RESEARCH-PGR: Zygotic Genome Activation in Rice

母本配子和父本配子融合形成合子，这标志着一个新植物从一个单细胞开始。这是植物生命周期的关键阶段。通过DNA和相关蛋白的化学修饰，基因表达模式的广泛重编程，也称为表观遗传过程，伴随着受精卵的发育。先前的研究表明，植物合子基因的大规模激活比动物更早发生；然而，母体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，由于难以在开花植物早期发育的精确时间点分离单细胞合子，因此尚未在开花植物中进行早期阶段合子基因组重编程和激活的详细表征。本项目将描述水稻（一种重要的作物植物）受精卵中由表观遗传机制介导的全基因组变化。本研究将探讨从受精开始的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展。了解从配子中形成合子在提高种子产量、从组织培养中再生植物以及改进杂交育种方法方面具有农业应用价值。该项目还将为兰斯顿大学（Langston University）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。兰斯顿大学是位于俄克拉荷马州的一所历史悠久的非裔美国人大学。水稻是研究受精卵基因组激活过程中基因组重编程相关机制的良好模型。水稻是开花植物中从传粉到受精时间最短的植物之一，这一特性使得分离出精确阶段的受精卵进行分析成为可能。合子基因组激活的表观遗传过程将通过对雄性和雌性配子以及自花授粉和杂交杂交的合子的小RNA转录组和甲基组的表征来阐明。目的包括鉴定靶向母体转录本的微rna，靶向转座子沉默的短干扰rna，以及潜在的参与合子染色质重置的新型小rna。将研究具有单代合子表达的位点的甲基化标记的传递或消除。该分析将纳入影响rna依赖性甲基化途径的突变体。这些数据集将用于在胚胎发生过程中产生亲本起源表达模型，以及转座元件的沉默和通过种系构建异色结构域的建立。该项目的成果将弥合对植物生命周期基本转变的理解上的主要差距。

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.