Dynamics of nuclear-mitochondrial interactions in the canola plant Brassica napus

病原体和宿主生物之间的遗传相互作用导致了遗传军备竞赛的概念：在病原体中进化基因，使其能够逃避宿主防御，作为回应，在宿主中进化基因，使其能够抵抗这些新的致病菌株。细胞质雄性不育(CMS)是高等植物普遍存在的一种性状，是线粒体DNA(MtDNA)中表达新的开放阅读框架(ORF)的结果。在许多情况下，被称为育性恢复者(RF)的核基因已被发现抑制CMS表型。这些恢复基因对特定形式的CMS是特异的，并通过下调与CMS相关的新的ORF的表达来发挥功能。CMS可以被视为一种特别有趣的“基因组内”类型的军备竞赛：母系遗传的CMS-赋予mtDNA在种群中传播，因为不将资源分配到花粉生产中的选择性优势；随着CMS个体变得更加频繁，花粉变得有限，为新的恢复系的进化创造了选择压力。我的实验室过去15年的研究揭示了油菜CMS/恢复者基因系统的特征，这表明这些系统可能为了解这场军备竞赛提供了有用的洞察。最近，我们发现包含两种甘蓝型油菜细胞质雄性不育基因排列的ORF存在于线粒体中，在亚化学计量水平上，它们不可能出现在线粒体中，包括甘蓝型油菜的一个祖先种的线粒体。此外，我们现在已经克隆并鉴定了一种形式的Brassica核恢复基因座。拟议的研究建立在最近的工作基础上，并可能使我们对CMS-恢复体系统如何进化有一个全面的了解。具体地说，我们将确定改变mt基因组配置是否会导致亚化学计量CMS相关基因排列的放大和雄性不育；我们将表征恢复基因的不同形式，以深入了解恢复基因进化的分子事件；我们将确定特定的恢复基因及其编码的蛋白质相互作用的分子。

The genetic interaction between pathogens and host organisms has led to the concept of a genetic arms race: genes evolve in pathogens that allow them to evade host defenses, and in response genes evolve in hosts that allow them to resist such new pathogenic strains. Cytoplasmic male sterility (CMS) is a widespread trait among higher plants that results from the expression of novel open reading frames (ORFs) in mitochondrial DNA (mtDNA). In many cases, nuclear genes termed restorers-of-fertility (Rf) have been identified that suppress the CMS phenotype. Such restorer genes are specific for a particular form of CMS and function by down-regulating the expression of the novel, CMS-associated ORF. CMS can be viewed as a particularly interesting "intra-genomic" type of arms race: maternally inherited CMS-conferring mtDNAs spread in a population due to the selective advantage of not allocating resources into pollen production; as CMS individuals become more frequent, pollen becomes limiting, creating the selective pressure for evolution of new restorers. Studies from my laboratory over the last 15 year have revealed features of CMS / restorer gene systems of the canola plant Brassica napus that suggest these systems may provide a useful insight into this arms race. More recently, we discovered that ORF containing gene arrangements responsible for the two forms of B. napus CMS are present at substoichiometric levels in mitochondria in which they are not expected to occur, including mitochondria of one of the progenitor species of B. napus. In addition, we have now cloned and characterized one form of the Brassica nuclear restorer locus. The proposed studies build on this recent work and may allow us to obtain a comprehensive understanding of how CMS-restorer systems evolve. Specifically, we will determine if alteration mt genomic configurations can lead to amplification of the substoichiometric CMS-associated gene arrangements and male sterility; we will characterize the different forms of the restorer locus to gain insight into the molecular events by which the restorers evolved; and we will identify specific restorer genes and the molecules the proteins they encode interact with.