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：病原体中的基因进化使它们能够逃避宿主的防御，而作为回应，宿主中的基因进化使它们能够抵抗这种新的致病菌株。细胞质雄性不育（Cytoplasmic male sterile， CMS）是高等植物普遍存在的一种性状，它是由线粒体DNA （mtDNA）中新型开放阅读框（open reading frame, orf）的表达引起的。在许多情况下，被称为生殖恢复（Rf）的核基因已被确定抑制CMS表型。这些恢复基因对一种特殊形式的CMS具有特异性，并通过下调新型CMS相关ORF的表达而起作用。CMS可以被视为一种特别有趣的“基因组内”类型的军备竞赛：由于不将资源分配给花粉生产的选择优势，母体遗传的CMS赋予mtdna在群体中传播；随着CMS个体变得更加频繁，花粉变得有限，为新恢复系的进化创造了选择压力。我的实验室在过去15年的研究中揭示了油菜植物甘蓝型油菜的CMS /恢复基因系统的特征，表明这些系统可能为这场军备竞赛提供有用的见解。最近，我们发现含有负责两种形式的甘蓝型油菜CMS的基因排列的ORF在线粒体中以亚化学计量水平存在，这是预期不会发生的，包括甘蓝型油菜的一个祖先物种的线粒体。此外，我们现在已经克隆和鉴定了一种形式的芸苔核恢复位点。拟议的研究建立在最近的工作基础上，并可能使我们对cms -恢复系统的演变有一个全面的了解。具体来说，我们将确定基因组结构的改变是否会导致亚化学计量学cms相关基因排列和男性不育的扩增；我们将描述不同形式的恢复位点，以深入了解恢复进化的分子事件；我们将识别特定的恢复基因以及它们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.