Botany Department, University of British Columbia, Vancouver, BC V6T 1Z4, Canada.
Botany Department, University of British Columbia, Vancouver, BC V6T 1Z4, Canada; Institute for Biology of Inland Waters, Russian Academy of Sciences, Borok, Yaroslavl Province 152742, Russian Federation.
Curr Biol. 2013 Dec 16;23(24):2546-52. doi: 10.1016/j.cub.2013.10.062. Epub 2013 Dec 5.
The alveolates comprise three well-studied protist lineages of significant environmental, medical, and economical importance: apicomplexans (e.g., Plasmodium), dinoflagellates (e.g., Symbiodinium), and ciliates (e.g., Tetrahymena). These major lineages have evolved distinct and unusual characteristics, the origins of which have proved to be difficult evolutionary puzzles. Mitochondrial genomes are a prime example: all three groups depart from canonical form and content, but in different ways. Reconstructing such ancient transitions is difficult without deep-branching lineages that retain ancestral characteristics. Here we describe two such lineages and how they illuminate the ancestral state of alveolate mitochondrial genomes. We established five clonal cultures of colponemids, predatory alveolates without cultured representatives and molecular data. Colponemids represent at least two independent lineages at the phylum level in multilocus phylogenetic analysis; one sister to apicomplexans and dinoflagellates, and the other at a deeper position. A genome survey from one strain showed that ancestral state of the mitochondrial genomes in the three major alveolate lineages consisted of an unusual linear chromosome with telomeres and a substantially larger gene set than known alveolates. Colponemid sequences also identified several environmental lineages as colponemids, altogether suggesting an untapped potential for understanding the origin and evolution of apicomplexans, dinoflagellates, and ciliates.
纤毛门包括三个研究充分的原生生物谱系，它们在环境、医学和经济方面具有重要意义：顶复门（例如疟原虫）、甲藻门（例如共生甲藻）和纤毛门（例如四膜虫）。这些主要谱系具有独特而不寻常的特征，其起源被证明是具有挑战性的进化难题。线粒体基因组就是一个很好的例子：这三个群体都偏离了典型的形式和内容，但方式不同。如果没有保留祖先特征的深分支谱系，重建这样的古老转变是很困难的。在这里，我们描述了两个这样的谱系，以及它们如何阐明纤毛门线粒体基因组的祖先状态。我们建立了五个无培养代表和分子数据的掠食性纤毛门科尔隆体的克隆培养物。科尔隆体在多基因座系统发育分析中至少代表了两个门水平上的独立谱系；一个与顶复门和甲藻门的姐妹关系，另一个在更深的位置。从一个菌株的基因组调查显示，在三个主要纤毛门谱系中，线粒体基因组的祖先状态由具有端粒的不寻常线性染色体和比已知纤毛门更大的基因集组成。科尔隆体序列还将几个环境谱系鉴定为科尔隆体，这表明在理解顶复门、甲藻门和纤毛门的起源和进化方面还有很大的潜力尚未开发。
