Yoon Hwan Su, Hackett Jeremiah D, Van Dolah Frances M, Nosenko Tetyana, Lidie Kristy L, Bhattacharya Debashish
Department of Biological Sciences and Roy J. Carver Center for Comparative Genomics, University of Iowa, USA.
Mol Biol Evol. 2005 May;22(5):1299-308. doi: 10.1093/molbev/msi118. Epub 2005 Mar 2.
Dinoflagellates are important aquatic primary producers and cause "red tides." The most widespread plastid (photosynthetic organelle) in these algae contains the unique accessory pigment peridinin. This plastid putatively originated via a red algal secondary endosymbiosis and has some remarkable features, the most notable being a genome that is reduced to 1-3 gene minicircles with about 14 genes (out of an original 130-200) remaining in the organelle and a nuclear-encoded proteobacterial Form II Rubisco. The "missing" plastid genes are relocated to the nucleus via a massive transfer unequaled in other photosynthetic eukaryotes. The fate of these characters is unknown in a number of dinoflagellates that have replaced the peridinin plastid through tertiary endosymbiosis. We addressed this issue in the fucoxanthin dinoflagellates (e.g., Karenia brevis) that contain a captured haptophyte plastid. Our multiprotein phylogenetic analyses provide robust support for the haptophyte plastid replacement and are consistent with a red algal origin of the chromalveolate plastid. We then generated an expressed sequence tag (EST) database of 5,138 unique genes from K. brevis and searched for nuclear genes of plastid function. The EST data indicate the loss of the ancestral peridinin plastid characters in K. brevis including the transferred plastid genes and Form II Rubisco. These results underline the remarkable ability of dinoflagellates to remodel their genomes through endosymbiosis and the considerable impact of this process on cell evolution.
甲藻是重要的水生初级生产者，并会引发“赤潮”。这些藻类中分布最广泛的质体（光合细胞器）含有独特的辅助色素多甲藻素。这种质体据推测起源于红藻的次生内共生，具有一些显著特征，最值得注意的是其基因组缩减为1至3个基因小环，细胞器中仅保留约14个基因（原本有130 - 200个），以及一个核编码的细菌II型核酮糖-1,5-二磷酸羧化酶/加氧酶。“缺失”的质体基因通过大规模转移重新定位到细胞核，这在其他光合真核生物中是无与伦比的。在一些通过三次内共生取代了多甲藻素质体的甲藻中，这些特征的命运尚不清楚。我们在含有捕获的定鞭藻质体的岩藻黄素甲藻（例如，短裸甲藻）中解决了这个问题。我们的多蛋白系统发育分析为定鞭藻质体的取代提供了有力支持，并且与色藻质体起源于红藻一致。然后，我们从短裸甲藻生成了一个包含5138个独特基因的表达序列标签（EST）数据库，并搜索质体功能的核基因。EST数据表明短裸甲藻中祖先多甲藻素质体特征的丧失，包括转移的质体基因和II型核酮糖-1,5-二磷酸羧化酶/加氧酶。这些结果强调了甲藻通过内共生重塑其基因组的显著能力以及这一过程对细胞进化的重大影响。
