The highly reduced genome of an enslaved algal nucleus
The highly reduced genome of an enslaved algal nucleus
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DOI：
10.1038/35074092
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发表时间：
2001-04-26
期刊：
影响因子：
64.8
通讯作者：
Maier, UG
中科院分区：
文献类型：
--
作者：
Douglas, S;Zauner, S;Maier, UG
有色藻类与植物的根本区别在于，它们拥有含有叶绿素c的叶绿体，并且具有更复杂的结合膜拓扑结构（1）。虽然已知有色植物是一种红色植物和一种非光合宿主的进化嵌合体（1），这导致了它们异常的膜复杂性，但对它们的细胞生物学知之甚少。隐藻是唯一一种仍然保留被奴役的红藻核作为微小核形物的有色植物（2-4）。在这里，我们报告的全部三个核形染色体的隐藻Guillardia θ的完整序列。这个微小的551-β-淀粉酶真核基因组是已知的基因密度最高的，只有17个小型剪接体内含子和44个重叠基因。数亿年前（1，4，5）显著的进化压缩消除了几乎所有的代谢功能的核形基因，但留下30个叶绿体定位的蛋白质。为了允许这些蛋白质的表达，核型体保留了数百个遗传管家基因（5）。核型DNA复制和周质体蛋白质合成需要许多核基因产物穿过内质网和周质体膜。染色体有着丝粒，但可能只有一个环状结构域，为研究真核生物染色体的复制、分离和进化提供了一种手段。
Chromophyte algae differ fundamentally from plants in possessing chloroplasts that contain chlorophyll c and that have a more complex bounding-membrane topology(1). Although chromophytes are known to be evolutionary chimaeras of a red alga and a non-photosynthetic host(1), which gave rise to their exceptional membrane complexity, their cell biology is poorly understood. Cryptomonads are the only chromophytes that still retain the enslaved red algal nucleus as a minute nucleomorph(2-4). Here we report complete sequences for all three nucleomorph chromosomes from the cryptomonad Guillardia theta. This tiny 551-kilobase eukaryotic genome is the most gene-dense known, with only 17 diminutive spliceosomal introns and 44 overlapping genes. Marked evolutionary compaction hundreds of millions of years ago(1,4,5) eliminated nearly all the nucleomorph genes for metabolic functions, but left 30 for chloroplast-located proteins. To allow expression of these proteins, nucleomorphs retain hundreds of genetic-housekeeping genes(5). Nucleomorph DNA replication and periplastid protein synthesis require the import of many nuclear gene products across endoplasmic reticulum and periplastid membranes. The chromosomes have centromeres, but possibly only one loop domain, offering a means for studying eukaryotic chromosome replication, segregation and evolution.