Nuclear Mechanisms that Influence Mitochondrial Genome Stability

植物线粒体基因组在其进化过程中获得了几个区别性特征，这些特征在机制上或进化背景下都没有得到很好的理解。 其中之一是不对称（非互惠）重组的过程，似乎直接影响植物繁殖。 到目前为止，我们对这些过程的理解一直受到阻碍，部分原因是没有有效的模型系统来研究核基因对该过程的影响。 三个核基因，MSH1，OSB1和RECA3，最近已经分析了线粒体基因组稳定性的影响。RECA3和MSH1在不同但重叠的途径中起作用，而OSB1与MSH1合作，调节拟南芥线粒体中特异性重组产物的出现。 主要研究人员最近表明，MSH1在烟草、番茄、大豆和小米中的功能相似，但这些物种中的MSH1 RNAi敲除也会导致细胞质雄性不育。主要研究人员现在能够分析线粒体基因组的变化，当这些核基因的突变允许通常罕见的重组活动以高频率发生时，并比较这种重组在多个植物物种中的后果。中心假设是MSH1，OSB1和RECA3，与基因组中的特定断裂位点一起，代表了在植物线粒体重组依赖性复制起始中起作用的相互作用网络的组成部分。主要研究人员提出，双链DNA断裂发生在线粒体基因组内的特定位置，以启动重组和复制，而MSH1，OSB1和RECA3参与防止短于几百个碱基的重复序列之间的重组。主要研究人员通过鉴定重复序列中的双链断裂以及Atp9、Atp6、CoxII和Rpl16基因中的双链断裂来测试这些假设，其中存在重组活性的证据。这种分析是由烟草，番茄，大豆和小米线粒体基因组发生MSH1抑制和雄性不育诱导诱导的诱导变化的研究补充。该项目将为植物线粒体基因组的重组依赖性复制开发一个统一的模型，并为细胞质雄性不育的诱导和抑制机制提供见解，细胞质雄性不育是一种具有农业重要性的现象，在自然界中，约5%的世界植物物种采用雌雄异株的生殖策略。与该提案相关的少数民族学生培训机会将与内布拉斯加州青年科学家（YNS）计划保持一致，其中一名YNS本科生将每年夏天参加这项研究。

The plant mitochondrial genome has acquired, during its evolution, several distinguishing features that are not well understood mechanistically or in evolutionary context. One of these is a process of asymmetric (non-reciprocal) recombination that appears to directly influence plant reproduction. Until now, our understanding of these processes has been hindered, in part, by the unavailability of effective model systems for investigating nuclear gene influence on the process. The effects of three nuclear genes, MSH1, OSB1 and RECA3, have recently been analyzed on mitochondrial genome stability. RECA3 and MSH1 function in distinct but overlapping pathways, while OSB1 cooperates with MSH1, to regulate the appearance of specific recombination products in Arabidopsis mitochondria. The principal investigators have recently shown that MSH1 functions similarly in tobacco, tomato, soybean and millet, but MSH1 RNAi knockdowns in these species also condition cytoplasmic male sterility. The principal investigators are now in a position to analyze the mitochondrial genome changes that occur when mutations in these nuclear genes permit normally rare recombination activity to occur at high frequency, and to compare the consequences of this recombination in multiple plant species. The central hypothesis is that MSH1, OSB1, and RECA3, together with specific breakage sites in the genome, represent components of an interacting network that operates in plant mitochondrial recombination-dependent replication initiation. The principal investigators propose that double-strand DNA breaks occur at specific locations within the mitochondrial genome to initiate recombination and replication, and that MSH1, OSB1 and RECA3 are involved in preventing recombination between repeats that are shorter than a few hundred bases. The principal investigators test these hypotheses by identifying double-strand breaks in repeated sequences, and in the Atp9, Atp6, CoxII and Rpl16 genes, in which there is evidence of recombination activity. This analysis is complemented by studies of inducible changes in tobacco, tomato, soybean and millet mitochondrial genomes that occur with MSH1 suppression and male sterility induction. This project will develop a unifying model for recombination-dependent replication of plant mitochondrial genomes, and provide insights into the mechanisms for the induction and suppression of cytoplasmic male sterility, a phenomenon of agricultural importance that leads, in nature, to the gynodioecious reproductive strategies of approximately 5% of world plant species. The minority student training opportunities associated with this proposal will involve alignment with the Young Nebraska Scientist (YNS) Program, in which an undergraduate YNS student will participate in this research each summer.