Plant mitochondria contain small extrachromosomal DNAs in addition to a large and complex main mitochondrial genome. These molecules can be regarded as extrachromosomal replicons or plasmids, of which there are two forms, circular and linear. Linear mitochondrial plasmids are present in many fungi and in some plants, but they seem to be absent from most animal cells. They usually have a common structural feature, called an invertron, that is characterized by the presence of terminal inverted repeats and proteins covalently attached to their 5 termini. Linear mitochondrial plasmids possess one to six ORFs that can encode unknown proteins but often code for the DNA and RNA polymerases. Although the functions of most linear plasmids in plant mitochondria are unknown, some plasmids may be associated with mitochondrial genome rearrangements and may have phenotypic effects due to their integration into mitochondrial genome. The Brassica 11.6-kb plasmid, one of the linear mitochondrial plasmids in plants, shows a non-maternal inheritance, in contrast to mitochondrial genomes. The origin of these plasmids is still a mystery, but indirect evidence indicates the possibility of horizontal transfer from fungal mitochondria. In this review, the main features of these unique DNAs present in plant mitochondria are described.

中文翻译：

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植物线粒体中的线性质粒：和平共处还是恶意入侵？

除了大而复杂的主要线粒体基因组外，植物线粒体还包含小的染色体外 DNA。这些分子可视为染色体外的复制子或质粒，有环状和线状两种形式。线性线粒体质粒存在于许多真菌和一些植物中，但它们似乎在大多数动物细胞中不存在。它们通常具有一个共同的结构特征，称为反相子，其特征在于存在末端反向重复序列和共价连接到其 5 个末端的蛋白质。线性线粒体质粒具有 1 到 6 个可编码未知蛋白质但通常编码 DNA 和 RNA 聚合酶的 ORF。尽管大多数线性质粒在植物线粒体中的功能尚不清楚，一些质粒可能与线粒体基因组重排有关，并且由于它们整合到线粒体基因组中而可能具有表型效应。与线粒体基因组相反，芸苔属 11.6-kb 质粒是植物中线性线粒体质粒之一，显示非母系遗传。这些质粒的起源仍然是个谜，但间接证据表明可能从真菌线粒体水平转移。在这篇综述中，描述了植物线粒体中存在的这些独特 DNA 的主要特征。但间接证据表明真菌线粒体水平转移的可能性。在这篇综述中，描述了植物线粒体中存在的这些独特 DNA 的主要特征。但间接证据表明真菌线粒体水平转移的可能性。在这篇综述中，描述了植物线粒体中存在的这些独特 DNA 的主要特征。