Mitochondrial genome of a tertiary endosymbiont retains genes for electron transport proteins
Mitochondrial genome of a tertiary endosymbiont retains genes for electron transport proteins
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DOI：
10.1111/j.1550-7408.2007.00245.x
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发表时间：
2007-03-01
影响因子：
2.2
通讯作者：
Keeling, Patrick J.
中科院分区：
文献类型：
--
作者：
Imanian, Behzad;Carpenter, Kevin J.;Keeling, Patrick J.
线粒体和质体起源于内共生，随后减少并以类似的方式与寄主整合。叶绿体通过进一步的二级甚至三级内共生在谱系之间传播，但线粒体似乎只起源一次，没有在谱系之间传播。线粒体通常也在次生和第三级内共生体中丢失，唯一的例外是硅藻第三级内共生体，如叶绿藻，据报道寄主和内共生体都含有线粒体。在这里，我们描述了这个系统中的第一个线粒体基因：细胞色素c氧化酶1(Cox1)、细胞色素氧化酶3(Cox3)和细胞色素b(Cob)。系统发育分析表明，所有特征基因都来自羽状硅藻内共生体，而不是寄主。我们还证明了这三个基因都得到了表达，cox1含有剪接的第II组内含子，cox3和cox3形成操纵子，都像它们的硅藻亲戚一样。内共生体线粒体不仅保留基因组，而且表达它们的基因，因此很可能参与电子传递。超微结构检查证实，内共生体线粒体保留了正常的管状脊。总体而言，这些数据表明，内共生体线粒体并没有在基因组或功能水平上减少。
Mitochondria and plastids originated through endosymbiosis, and subsequently became reduced and integrated with the host in similar ways. Plastids spread between lineages through further secondary or even tertiary endosymbioses, but mitochondria appear to have originated once and have not spread between lineages. Mitochondria are also generally lost in secondary and tertiary endosymbionts, with the single exception of the diatom tertiary endosymbiont of dinoflagellates like Kryptoperidinium foliaceum, where both host and endosymbiont are reported to contain mitochondria. Here we describe the first mitochondrial genes from this system: cytochrome c oxidase 1 (cox1), cytochrome oxidase 3 (cox3), and cytochrome b (cob). Phylogenetic analyses demonstrated that all characterized genes were derived from the pennate diatom endosymbiont, and not the host. We also demonstrated that all three genes are expressed, that cox1 contains spliced group II introns, and that cob and cox3 form an operon, all like their diatom relatives. The endosymbiont mitochondria not only retain a genome, but also express their genes, and are therefore likely involved in electron transport. Ultrastructural examination confirmed the endosymbiont mitochondria retain normal tubular cristae. Overall, these data suggest the endosymbiont mitochondria have not reduced at the genomic or functional level.