Genetics of Maize Mitochondria

一个长期项目将继续，以阐明突变是如何在植物线粒体中产生和恢复的，以及这些突变对植物表型和细胞功能有什么影响。关于在异质玉米植株中繁殖的一组致命线粒体突变(非染色体)条纹(NCS)对细胞功能的影响的调查将继续进行。最近发现，在所有的NCS突变体中，两种核编码的植物线粒体应激蛋白，交替氧化酶(AOX)和HSP22都显著增加。有人建议确定这种诱导发生在什么水平，并确定在NCS植物中存在差异调控的其他线粒体蛋白。第二个目标是了解植物线粒体基因组的完整性是如何维持的。基因组在体内以一组亚基因组的形式存在，这些亚基因组是由活跃的重组产生的。尽管如此，线粒体基因型及其亚基因组互补通常会从母本忠实地传递给后代。在一个特殊的玉米品系P2中，人们发现线粒体基因组的变异令人惊讶，而且新的、小的亚基因组被扩增到高水平。假设这些小的线粒体DNA环带有复制的起源，从而允许它们的放大，这一假设将得到验证。其中两个独立扩增的小亚组在杂交中被发现是母系可遗传的，这可能有助于识别线粒体基因组中对适当分离和有效复制mtDNA至关重要的区域。由于线粒体在细胞程序性死亡、氧化应激和细胞器逆行调节等现象中的中心作用，人们对线粒体的兴趣最近有所增强。在逆行调控中，某些核基因的表达被转录激活，以响应细胞器代谢状态的变化。这项研究的结果将进一步深入了解线粒体功能的基因组调控。

A long-term project to elucidate how mutations are generated and recovered in plant mitochondria and what effects these mutations have on plant phenotypes and cellular function will be continued. An investigation into the effects on cellular function of a set of lethal mitochondrial mutations (nonchromosomal) stripe, NCS) that are propagated in heteroplasmic maize plants will be continued. It has been recently found that two types of nucleus-encoded plant mitochondrial stress proteins, alternative oxidase (AOX) and HSP22 are dramatically increased in all of the NCS mutants. It is proposed to determine at what level this induction occurs and to identify other mitochondrial proteins that are differentially regulated in NCS plants. A second objective is to learn how the integrity of plant mitochondrial genomes is maintained. The genomes exist in vivo as a collection of subgenomes, which result from active recombination. Nonetheless, mitochondrial genotypes and their subgenomic complements are usually faithfully transmitted from maternal parent to progeny. In an exceptional line of maize, P2, it has been found that nitochondrial genomes are surprisingly variable and that novel, small subgenomes are amplified to high levels. The hypothesis that these small mtDNA circles carry origins of replication that allow their amplification will be tested. Two of the independently amplified small subgenomes have been found to be maternally heritable in crosses, which may help to identify those regions of the mitochondrial genome that are critical for the proper segregation and efficient replication of mtDNA.Interest in mitochondria has intensified recently due to their central roles in phenomena such as programmed cell death, oxidative stress and organellar retrograde regulation. In retrograde regulation, the expression of certain nuclear genes is transcriptionally activated in response to changes in the metabolic state of organelles. The results of this investigation will give further insight into the genomic regulation of mitrochondrial function.