Imanian Behzad, Keeling Patrick J
Department of Botany, Canadian Institute for Advanced Research, University of British Columbia, Vancouver, British Columbia, Canada.
Genome Biol Evol. 2014 Feb;6(2):333-43. doi: 10.1093/gbe/evu014.
A tertiary endosymbiosis between a dinoflagellate host and diatom endosymbiont gave rise to "dinotoms," cells with a unique nuclear and mitochondrial redundancy derived from two evolutionarily distinct eukaryotic lineages. To examine how this unique redundancy might have affected the evolution of metabolic systems, we investigated the transcription of genes involved in biosynthesis of the amino acid tryptophan in three species, Durinskia baltica, Kryptoperidinium foliaceum, and Glenodinium foliaceum. From transcriptome sequence data, we recovered two distinct sets of protein-coding transcripts covering the entire tryptophan biosynthetic pathway. Phylogenetic analyses suggest a diatom origin for one set of the proteins, which we infer to be expressed in the endosymbiont, and that the other arose from multiple horizontal gene transfer events to the dinoflagellate ancestor of the host lineage. This is the first indication that these cells retain redundant sets of transcripts and likely metabolic pathways for the biosynthesis of small molecules and extend their redundancy to their two distinct nuclear genomes.
在一个甲藻宿主和硅藻内共生体之间的第三次内共生产生了“甲藻硅藻复合体”，这些细胞具有独特的细胞核和线粒体冗余，其来源于两个在进化上不同的真核生物谱系。为了研究这种独特的冗余可能如何影响代谢系统的进化，我们调查了波罗的海杜氏藻、叶状隐甲藻和叶状格氏藻这三个物种中参与色氨酸生物合成的基因转录情况。从转录组序列数据中，我们获得了两套不同的蛋白质编码转录本，它们覆盖了整个色氨酸生物合成途径。系统发育分析表明，其中一组蛋白质起源于硅藻，我们推断这组蛋白质在共生体中表达，而另一组则来自多次水平基因转移事件，转移到宿主谱系的甲藻祖先中。这首次表明，这些细胞保留了用于小分子生物合成的冗余转录本集和可能的代谢途径，并将其冗余扩展到它们两个不同的细胞核基因组中。
