Uncovering the molecular mechanism of paramutation, a classic example of non-Mendelian inheritance in maize

揭示副突变的分子机制，玉米非孟德尔遗传的经典例子

• 批准号: 1715375
• 负责人: Jay Hollick
• 金额: $ 66万
• 依托单位: Ohio State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2017
• 资助国家: 美国
• 起止时间: 2017-07-15 至 2023-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1715375&HistoricalAwards=false
• 关键词: Uncovering; molecular; mechanism; paramutation; classic

This project investigates a biological mechanism, called paramutation, which is responsible for turning selected genes "on" and "off" in highly predictable ways and for passing these "on" and "off" states to future generations. Similar to the well-known process of mutation, paramutation generates heritable biological variation that impacts evolutionary success. Unlike mutations, however, paramutations occur without changes to the DNA code. The project thus addresses an exception to an established rule of modern genetics by asking how regulatory information is altered and transmitted to offspring in the absence of DNA changes. The work will be carried out in corn, the preeminent model for studying the paramutation mechanism because the "on" and "off" states of genes responsible for plant color are visually tracked, controlled matings are simple to perform, and detailed multigenerational pedigrees can be generated and evaluated. A working model for paramutation has been proposed based on research and this project tests specific aspects of that model. The project will also identify novel molecules and chromosome structures responsible for the "on" and "off" switching during paramutations. Because paramutation occurs in both plants and animals, the results of this research could have broad biological impact, ranging from increased understanding of reproductive biology and genetics to development of novel strategies for improving agriculture or animal health. Educational materials such as colorful corn ears will be generated and made available through existing outreach programs for teaching both basic and advanced genetic concepts in the classroom. The activities integrate the training of young scientists at undergraduate and graduate levels as well as provide research experiences for high school students. Paramutation describes a behavior in which specific trans-homolog interactions result in meiotically-heritable regulatory alterations. This behavior is potentially mediated by small RNAs but the mechanism remain largely unknown. A model system was developed using plant and flower color to define the molecular mechanism of paramutation occurring in maize. Expression of the purple plant1 gene is monitored with visible pigments. A strong purple state of the Pl1-Rhoades (Pl1-Rh) allele can change to weaker expression states referred to as Pl'. When purple types (Pl/Pl) are mated with weakly pigmented plants (Pl/Pl'), only weakly pigmented progeny - from which only Pl' states are sexually transmitted - are obtained; this is a classic example of paramutation. Forward genetics identifies important cis-acting regions and fifteen loci whose functions are required to maintain repression (rmr) of Pl' states. Prior projects helped identify five RMR proteins acting in a presumed small RNA-directed DNA methylation pathway and led to the discovery of a co-transcriptional repression mechanism operating to maintain meiotically-heritable regulatory states established by paramutation. This project builds on this emerging mechanistic understanding by combining forward genetics, molecular profiling, and mutant analyses to specifically 1) test working models of the paramutation mechanism by profiling transcription, small RNA levels, and cytosine methylation patterns during paramutation events, 2) functionally define cis-acting sequences responsible for paramutation behaviors through structural characterizations of mutant Pl1-Rh alleles, and 3) discover additional molecular components governing paramutations through positional-based cloning of additional rmr loci. Training and outreach opportunities are integrated in these efforts to provide a greater understanding of fundamental eukaryotic genetics and genome biology.This project is jointly funded by the Genetics Mechanisms Cluster in the Division of Molecular and Cellular Biosciences and the Plant Genome Research Program in the Division of Integrative Organismal Systems.

该项目研究了一种称为副突变的生物机制，它负责以高度可预测的方式“打开”和“关闭”选定的基因，并将这些“打开”和“关闭”状态传递给后代。 与众所周知的突变过程类似，副突变会产生可遗传的生物变异，从而影响进化的成功。然而，与突变不同的是，副突变的发生并不改变 DNA 密码。因此，该项目通过询问在没有 DNA 变化的情况下监管信息如何被改变并传递给后代，解决了现代遗传学既定规则的一个例外。这项工作将在玉米中进行，玉米是研究副突变机制的卓越模型，因为负责植物颜色的基因的“开”和“关”状态可以通过视觉追踪，受控交配易于执行，并且可以生成和评估详细的多代谱系。根据研究提出了副突变的工作模型，该项目测试了该模型的特定方面。该项目还将确定负责副突变期间“开”和“关”切换的新分子和染色体结构。由于副突变发生在植物和动物中，因此这项研究的结果可能会产生广泛的生物学影响，从增进对生殖生物学和遗传学的了解到制定改善农业或动物健康的新策略。将制作并通过现有的外展计划提供彩色玉米穗等教育材料，用于在课堂上教授基本和高级遗传概念。这些活动结合了本科生和研究生水平的年轻科学家的培训，并为高中生提供研究经验。副突变描述了一种行为，其中特定的反式同源物相互作用导致减数分裂可遗传的调节改变。这种行为可能是由小 RNA 介导的，但其机制仍然很大程度上未知。使用植物和花的颜色开发了一个模型系统来定义玉米中发生副突变的分子机制。用可见色素监测紫色 plant1 基因的表达。 Pl1-Rhoades (Pl1-Rh) 等位基因的强紫色状态可以转变为较弱的表达状态，称为 Pl'。当紫色类型 (Pl/Pl) 与弱色素植物 (Pl/Pl') 交配时，仅获得弱色素后代 - 仅通过性传播 Pl' 状态；这是副突变的一个经典例子。正向遗传学鉴定了重要的顺式作用区域和十五个基因座，其功能是维持 Pl' 状态的抑制 (rmr) 所必需的。先前的项目帮助识别了在假定的小RNA引导的DNA甲基化途径中起作用的五种RMR蛋白，并导致发现了一种共转录抑制机制，该机制可维持由副突变建立的减数分裂遗传调节状态。该项目以这种新兴的机制理解为基础，通过结合正向遗传学、分子分析和突变分析来具体实现：1) 通过分析副突变事件期间的转录、小 RNA 水平和胞嘧啶甲基化模式来测试副突变机制的工作模型，2) 通过突变 Pl1-Rh 等位基因的结构表征，功能性地定义负责副突变行为的顺式作用序列，3) 发现其他分子 通过额外 rmr 位点的基于位置的克隆来控制副突变的组件。这些工作中融入了培训和外展机会，以更好地了解基础真核遗传学和基因组生物学。该项目由分子和细胞生物科学部的遗传学机制集群和综合有机体系统部的植物基因组研究计划联合资助。