Control of Organelle Inheritance

9723970与大多数有性真核生物一样，绿藻衣藻以单亲方式将细胞器DNA传递给有性后代，其减数分裂的4个产物都继承了交配型正亲(Mt)亲本提供的叶绿体DNA，所有4种减数分裂产物都继承了交配型减(mt-)亲本贡献的线粒体DNA。这些非孟德尔模式在40多年前由Sager首次注意到，已被证明是早期受精卵中叶绿体减去基因组和线粒体减去基因组的选择性降解的结果，但关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尚不清楚。大多数研究都集中在叶绿体DNA的单亲遗传上。该系统的主要保护者/破坏者模型认为，mt基因座编码保护者(S)，保护者与正配子中的叶绿体DNA结合和/或修改。然后，破坏者功能会退化受精卵中所有非保护性的、负衍生的基因组。这个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，但当它们交配时，它们的叶绿体DNA在受精卵中不会降解，结果是叶绿体标记的单亲(BP)遗传。这表明mt基因座编码保护叶绿体dna免受降解的基因(S)，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，我们相信，已经确定了该基因座上的一个基因，它是正配子交配所必需的。剩下的DNA片段还没有确定的功能。这一提议的工作前提是这些序列包含参与叶绿体DNA保护的基因。这项拟议的研究的目标是识别和表征这些基因，从而更好地了解S是如何实现保护的。我们提出了一种两级筛选。1)首次通过Northern分析鉴定了克隆的mt序列中的Plus专一性基因。2)然后将这些基因转化到mt受体中，并测试转化子参与BP遗传的能力。该屏幕的第一种状态已在中试实验中成功进行。已在Northern blotts中鉴定出一个与mt连锁的基因，并对其进行了序列测定。该基因产物有几个特征，表明它是一个转录调节因子。动物和真菌谱系设计出了监控它们线粒体基因组的未知机制；植物谱系则同时跟踪线粒体和叶绿体染色体。在衣藻正负交配型细胞配子融合形成的合子发育的最初几个小时内，mt亲本贡献的叶绿体基因组被破坏，mt贡献的线粒体基因组被破坏。这项工作的结果将使人们能够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.