Elimination of deleterious mutations in plastid genomes by gene conversion
Elimination of deleterious mutations in plastid genomes by gene conversion
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DOI：
10.1111/j.1365-313x.2006.02673.x
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发表时间：
2006-04-01
期刊：
影响因子：
7.2
通讯作者：
Bock, R
中科院分区：
文献类型：
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作者：
Khakhlova, O;Bock, R
无性繁殖被认为是有害的，主要是因为随着时间的推移，有害突变的积累，这一假说被称为穆勒棘轮。在种子植物中，大多数无性繁殖的遗传系统是多倍体的，无融合生殖物种(植物在没有受精的情况下形成种子)以及叶绿体和线粒体提供了突出的例子。多倍体是否有助于无性遗传系统逃脱穆勒的棘轮尚不清楚。基因转换，特别是当略有偏见时，代表了一种潜在的机制，可以允许无性遗传系统以依赖于基因组拷贝数的方式减少它们的突变负荷。然而，基因组分子之间的基因转换操作以纠正突变的直接实验证据在很大程度上是缺乏的。在这里，我们描述了一个基于转基因烟草叶绿体的实验系统，它允许我们分析高等植物叶绿体基因组中的基因转换事件。我们提供了基因转化作为一种高效机制的证据，通过这种机制，多倍体遗传系统可以纠正有害突变，并从两个不好的基因组中产生一个好基因组。我们的发现，基因转换可能是有偏见的，这可能提供了无性繁殖、高基因组拷贝数和低突变率之间的分子联系。
Asexual reproduction is believed to be detrimental, mainly because of the accumulation of deleterious mutations over time, a hypothesis known as Muller's ratchet. In seed plants, most asexually reproducing genetic systems are polyploid, with apomictic species (plants forming seeds without fertilization) as well as plastids and mitochondria providing prominent examples. Whether or not polyploidy helps asexual genetic systems to escape Muller's ratchet is unknown. Gene conversion, particularly when slightly biased, represents a potential mechanism that could allow asexual genetic systems to reduce their mutation load in a genome copy number-dependent manner. However, direct experimental evidence for the operation of gene conversion between genome molecules to correct mutations is largely lacking. Here we describe an experimental system based on transgenic tobacco chloroplasts that allows us to analyze gene conversion events in higher plant plastid genomes. We provide evidence for gene conversion acting as a highly efficient mechanism by which the polyploid plastid genetic system can correct deleterious mutations and make one good genome out of two bad ones. Our finding that gene conversion can be biased may provide a molecular link between asexual reproduction, high genome copy numbers and low mutation rates.