Department of Biology, University of Konstanz, Konstanz, Baden-Württemberg, 78457, Germany.
Department of Biological Sciences, University of Cape Town, Cape Town, Western Cape, 7701, South Africa.
Sci Rep. 2019 Jul 19;9(1):10474. doi: 10.1038/s41598-019-46852-y.
A monophyletic group of dinoflagellates, called 'dinotoms', are known to possess evolutionarily intermediate plastids derived from diatoms. The diatoms maintain their nuclei, mitochondria, and the endoplasmic reticulum in addition with their plastids, while it has been observed that the host dinoflagellates retain the diatoms permanently by controlling diatom karyokinesis. Previously, we showed that dinotoms have repeatedly replaced their diatoms. Here, we show the process of replacements is at two different evolutionary stages in two closely related dinotoms, Durinskia capensis and D. kwazulunatalensis. We clarify that D. capensis is a kleptoplastic protist keeping its diatoms temporarily, only for two months. On the other hand, D. kwazulunatalensis is able to keep several diatoms permanently and exhibits unique dynamics to maintain the diatom nuclei: the nuclei change their morphologies into a complex string-shape alongside the plastids during interphase and these string-shaped nuclei then condense into multiple round nuclei when the host divides. These dynamics have been observed in other dinotoms that possess permanent diatoms, while they have never been observed in any other eukaryotes. We suggest that the establishment of this unique mechanism might be a critical step for dinotoms to be able to convert kleptoplastids into permanent plastids.
一类称为“甲藻虫”的甲藻是已知的从硅藻中进化而来的具有中间质体的单系群体。硅藻除了拥有质体外，还保留着它们的细胞核、线粒体和内质网，而人们观察到，宿主甲藻通过控制硅藻有丝分裂，将硅藻永久保留下来。此前，我们已经表明，甲藻虫已经反复取代了它们的硅藻。在这里，我们展示了在两个密切相关的甲藻虫（南非 Durinskia capensis 和夸祖鲁-纳塔尔 D. kwazulunatalensis）中，这种取代过程发生在两个不同的进化阶段。我们澄清了南非 Durinskia capensis 是一个暂时保留其硅藻的偷食质体原生生物，只有两个月的时间。另一方面，D. kwazulunatalensis 能够永久保留几个硅藻，并表现出独特的动态来维持硅藻的细胞核：在间期中，细胞核与质体一起改变形态，形成复杂的线状，而当宿主分裂时，这些线状细胞核会浓缩成多个圆形细胞核。这些动态已经在其他拥有永久性硅藻的甲藻虫中观察到，但在任何其他真核生物中从未观察到过。我们认为，这种独特机制的确立可能是甲藻虫能够将偷食质体转化为永久性质体的关键步骤。
