RESEARCH-PGR: Zygotic Genome Activation in Rice

母本和父本配子的融合形成合子，它标志着从单个细胞开始形成新植物。这是植物生命周期中的一个关键阶段。通过DNA和相关蛋白质的化学修饰（也称为表观遗传过程）对基因表达模式进行广泛的重新编程，伴随着受精卵的发育。 以往的研究表明，植物合子基因的大规模激活发生早于它在动物中，然而，无论是时间和相对贡献的母亲和父亲的遗传物质合子基因激活没有得到很好的定义。此外，由于在早期发育过程中难以在精确的时间点分离单细胞合子，因此尚未在开花植物中进行合子基因组在最早阶段的重编程和激活的详细表征。 该项目将表征水稻（一种重要的作物）合子中由表观遗传机制介导的全基因组变化。这项研究将解决受精卵发育的早期阶段，从受精开始，并将利用最新的技术进步，在单细胞的分离和分子分析。了解配子形成合子的过程在农业上有着广泛的应用，如提高种子产量、从组织培养中再生植株、改良杂交育种方法等。 该项目还将为来自俄克拉荷马州的一所历史上的非洲裔美国人机构兰斯顿大学的学生和教师提供植物生物学和基因组学方面的培训。水稻是研究合子基因组激活期间基因组重编程相关机制的一个极好的模型。水稻是开花植物中从授粉到受精的时间最短的植物之一，这一特性使得分离精确分期的合子用于分析成为可能。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的小RNA转录组和甲基化组以及自花授粉和杂交产生的合子的表征来阐明。其目的包括鉴定靶向母体转录本的微小RNA、靶向转座子沉默的短干扰RNA以及参与合子染色质重置的潜在新型小RNA。将研究具有单亲合子表达的基因座的甲基化标记的传递或擦除。该分析将纳入影响RNA依赖性甲基化途径的突变体。这些数据集将用于生成胚胎发生中亲本来源表达的模型，以及转座因子沉默和通过种系建立组成性异染色质结构域的模型。 该项目的成果将导致弥合在理解植物生命周期的根本性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.