Plant mitochondrial genomes vary widely in size. Although many plant mitochondrial genomes have been sequenced and assembled, the vast majority are of angiosperms, and few are of gymnosperms. Most plant mitochondrial genomes are smaller than a megabase, with a few notable exceptions. We have sequenced and assembled the complete 5.5 Mbp mitochondrial genome of Sitka spruce (Picea sitchensis), to date, one of the largest mitochondrial genomes of a gymnosperm. We sequenced the whole genome using Oxford Nanopore MinION, and then identified contigs of mitochondrial origin assembled from these long reads based on sequence homology to the white spruce mitochondrial genome. The assembly graph shows a multipartite genome structure, composed of one smaller 168 kbp circular segment of DNA, and a larger 5.4 Mbp single component with a branching structure. The assembly graph gives insight into a putative complex physical genome structure, and its branching points may represent active sites of recombination.

中文翻译：

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裸子植物Sitka Spruce（Picea sitchensis）的完整线粒体基因组表明其物理结构复杂。

植物线粒体基因组的大小差异很大。尽管已对许多植物线粒体基因组进行了测序和组装，但绝大多数是被子植物，而很少是裸子植物。除少数值得注意的例外，大多数植物线粒体基因组都小于兆碱基。到目前为止，我们已经测序并组装了Sitka云杉（Picea sitchensis）的完整5.5 Mbp线粒体基因组，这是裸子植物最大的线粒体基因组之一。我们使用牛津纳米孔MinION对整个基因组进行了测序，然后基于与白色云杉线粒体基因组的序列同源性，从这些长读段中鉴定了线粒体起源的重叠群。组装图显示了一个多部分基因组结构，由一个较小的168 kbp环状DNA片段和一个较大的5.4 Mbp具有分支结构的单组分组成。