Morozov A A, Galachyants Yuri P
Limnological Institute SB RAS, 3, Ulan-Batorskaya, P.O. box 278, Irkutsk 664033, Russia.
Limnological Institute SB RAS, 3, Ulan-Batorskaya, P.O. box 278, Irkutsk 664033, Russia.
Mar Genomics. 2019 Jun;45:72-78. doi: 10.1016/j.margen.2019.02.003. Epub 2019 Feb 19.
Previous phylogenomic analyses of diatoms have discovered some plastid-targeted genes apparently coming from green algae. Number of these genes varied from less than a half of EGT-compatible genes to an overwhelming majority, and their presence was treated as an evidence of cryptic green plastid. We have performed such an analysis with a novel weighted approach on an extended dataset of diatom genomes and proteomes. Approximately equal evidence was found for red and green algal origins for diatoms genes. Considering that very similar results were obtained on other secondary photosynthetic groups whose endosymbioses were independent from that of the diatom ancestors, we consider the serial plastid replacements unparsimonious. A better explanation of these data can be provided by the shopping bag model, where a future host switches numerous endosymbionts and acquires some genes from each of them. Eventually the host loses the ability to replace endosymbionts (e.g. through the loss of phagotrophy) and whatever symbiont was present at the moment gets fixed and reduced to an organelle.
先前对硅藻的系统基因组分析发现，一些质体靶向基因显然来自绿藻。这些基因的数量从不到一半的与内共生基因转移（EGT）兼容的基因到绝大多数不等，它们的存在被视为隐秘绿色质体的证据。我们使用一种新颖的加权方法，对扩展的硅藻基因组和蛋白质组数据集进行了这样的分析。发现硅藻基因的红藻和绿藻起源的证据大致相当。鉴于在其他次生光合类群上也获得了非常相似的结果，而这些类群的内共生事件与硅藻祖先的内共生事件无关，我们认为连续的质体替代是不合理的。购物袋模型可以更好地解释这些数据，即未来的宿主切换众多内共生体，并从每个内共生体中获取一些基因。最终，宿主失去了替换内共生体的能力（例如通过吞噬营养的丧失），此时存在的任何共生体都会固定下来并简化为一个细胞器。
