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学机制，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。 类似于众所周知的突变过程，副突变产生影响进化成功的可遗传生物变异。然而，与突变不同的是，副突变的发生不会改变DNA密码。因此，该项目解决了现代遗传学既定规则的一个例外，即在没有DNA变化的情况下，调控信息是如何改变并传递给后代的。这项工作将在玉米中进行，玉米是研究副突变机制的杰出模型，因为负责植物颜色的基因的“开”和“关”状态可以直观地跟踪，控制交配易于执行，并且可以生成和评估详细的多代谱系。根据研究提出了一个准突变的工作模型，本项目测试了该模型的具体方面。该项目还将确定新的分子和染色体结构，负责在副突变期间的“开”和“关”开关。由于植物和动物都发生副突变，因此这项研究的结果可能会产生广泛的生物学影响，从增加对生殖生物学和遗传学的了解到开发改善农业或动物健康的新策略。将通过现有的推广方案制作和提供彩色玉米穗等教育材料，在课堂上教授基本和高级遗传概念。这些活动整合了对本科生和研究生一级青年科学家的培训，并为高中生提供研究经验。平行变异描述了一种行为，其中特定的反式同源物相互作用导致减数分裂遗传的调节改变。这种行为可能是由小RNA介导的，但其机制在很大程度上仍然未知。建立了一个利用植物和花的颜色来确定玉米副突变发生的分子机制的模型系统。用可见色素监测紫色植物1基因的表达。Pl 1-Rhoades（Pl 1-Rh）等位基因的强紫色状态可以改变为称为P1 '的较弱表达状态。当紫色类型（P1/P1）与弱色素植物（P1/P1 '）交配时，只获得弱色素后代-只有P1'状态是性传播的-这是副突变的典型例子。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。先前的项目帮助鉴定了五种RMR蛋白，它们在假定的小RNA指导的DNA甲基化途径中起作用，并导致发现了一种共转录抑制机制，该机制用于维持由副突变建立的减数分裂遗传调节状态。该项目建立在这种新兴的机制理解的基础上，通过结合正向遗传学，分子谱分析和突变体分析，具体地1）通过分析转录，小RNA水平和副突变事件期间的胞嘧啶甲基化模式来测试副突变机制的工作模型，2）通过突变体Pl 1-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，和3）通过另外的RMR基因座的基于位置的克隆发现控制副突变的另外的分子组分。本项目由分子和细胞生物科学部遗传机制组和综合有机体系统部植物基因组研究计划共同资助。