Control of Organelle Inheritance

9723970 Goodenough与大多数有性真核生物一样，绿色莱茵衣藻以单亲方式将其细胞器DNA传递给有性后代，减数分裂的所有4种产物都继承了交配型加（mt+）亲本贡献的叶绿体DNA，所有4种产物都继承了交配型减（mt-）亲本贡献的线粒体DNA。 Sager在40多年前首次注意到这些非孟德尔模式，已被证明是早期合子中负叶绿体基因组和正线粒体基因组选择性降解的结果，但对于在这个或任何其他系统中如何在分子水平上发生选择或破坏过程还一无所知。 大多数研究集中在叶绿体DNA的单亲遗传。 该系统运行的显性保护者/破坏者模型提出，mt+基因座编码保护者，其结合和/或修饰正配子中的叶绿体DNA。 然后，Destroyer功能降解受精卵中所有未受保护的负衍生基因组。 该模型的关键是观察到当mt-配子也携带mt+基因座时，它们分化为负配子，但是当它们交配时，它们的叶绿体DNA在合子中不降解，结果是叶绿体标记的单亲（BP）遗传。 这一观察结果表明，mt+基因座编码参与保护叶绿体DNA免受降解的基因，并证明这些基因即使在细胞经历负配子分化时也可以表达。我们最近克隆了mt+（和mt-）基因座，并且我们相信，在该基因座中确定了一个正配子交配所必需的基因。 还有一些DNA块没有确定的功能。 这个建议的工作前提是，这些序列包含叶绿体DNA保护基因。 拟议研究的目标是识别和表征这些基因，从而更好地了解如何实现保护。 我们提出了一个两阶段的屏幕。1)首先通过北方分析鉴定克隆的mt+序列中的plus特异性基因。 2)然后将基因转化到mt+受体中，并测试转化体参与BP遗传的能力。 该屏幕的第一状态已在试点实验中成功地进行。 在北方印迹中鉴定了一个与mt+连锁的具有plus特异性表达的基因，并对其cDNA进行了测序。 该基因产物具有几个特征，表明它是一种转录调节因子。 动物和真菌谱系已经设计出了未知的机制来监测它们的线粒体基因组;植物谱系保持对线粒体和叶绿体染色体的跟踪。在由衣原体的正交配型细胞和负交配型细胞的配子融合形成的合子发育的最初几个小时期间，由mt-亲本贡献的叶绿体基因组被破坏，并且由mt+贡献的线粒体基因组被破坏。这项工作的结果将使人们更深入地了解这一显着的基因歧视过程。

9723970 Goodenough Like most sexual eukaryotes, the green alga Chlamydomonas reinhardtii transmits its organelle DNA to its sexual progeny in a uniparental fashion, with all 4 products of meiosis inheriting the chloroplast DNA contributed by the mating-type plus (mt+) parent and all 4 inheriting the mitochondrial DNA contributed by the mating-type minus (mt-) parent. These non-Mendelian patterns, first noticed by Sager over 40 years ago, have been shown to be the result of the selective degradation of minus chloroplast genomes and plus mitochondrial genomes in the early zygote, but nothing is yet known about how the selection or the destruction process occurs at a molecular level in this or any other system. Most studies have focused on the uniparental inheritance of chloroplast DNA. The dominant Protector/Destroyer model for the operation of this system proposes that the mt+ locus encodes Protector(s) which binds to and/or modifies chloroplast DNA in the plus gamete. A Destroyer function then degrades all non-protected, minus-derived genomes in the zygote. Key to this model is the observation that when mt- gametes also carry an mt+ locus, they differentiate as minus gametes, but, when they are mated, their chloroplast DNA is not degraded in the zygote, the result being uniparental (BP) inheritance of chloroplast markers. This observation indicates that the mt+ locus encodes gene(s) involved in protecting chloroplast DNA from degradation, and documents that these genes can be expressed even when the cells undergo minus gametic differentiation.. We have recently cloned the mt+ (and the mt-) locus and have, we believe, identified the one gene in the locus that is necessary for plus gametes to mate. There remain blocks of DNA with no identified function. The working premise of this proposal is that these sequences contain genes involved in chloroplast DNA protection. The goal of the proposed research is to identify and characterize these genes and hence better understand how protection i s achieved. We propose a two-stage screen. 1) Plus-specific genes in the cloned mt+ sequences are first identified by northern analysis. 2) The genes are then transformed into mt+ recipients, and the transformants are tested for their capacity to engage in BP inheritance. The first state of this screen has been carried out successfully in pilot experiments. A mt+- linked gene with plus-specific expression has been identified in northern blots and its cDNA has been sequenced. The gene product has features several suggesting that it is a transcriptional regulator. Animal and fungal lineage's have devised uncharacterized mechanisms to monitor their mitochondrial genomes; plant lineage's keep track of both mitochondrial and chloroplast chromosomes. During the first few hours of zygote development formed by the fusion of gametes of plus and minus mating type cells of Chlamydomonas, the chloroplast genomes contributed by the mt- parent are destroyed and the mitochondria genomes contributed by the mt+ are destroyed. The results of this work will allow greater insight into this remarkable process of genetic discrimination.