Dinoflagellates with relic endosymbiont nuclei as models for elucidating organellogenesis
Dinoflagellates with relic endosymbiont nuclei as models for elucidating organellogenesis
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具有残余内共生核的甲藻作为阐明细胞器发生的模型
DOI：
10.1073/pnas.1911884117
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发表时间：
2020
影响因子：
11.1
通讯作者：
Yuji Inagaki
中科院分区：
文献类型：
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作者：
Chihiro Sarai;Goro Tanifuji;Takuro Nakayama;Ryoma Kamikawa;Kazuo Takahashi;Euki Yazaki;Eriko Matsuo;Ken-ichiro Ishida;Mitsuhisa Iwataki;Yuji Inagaki
核形是迄今为止仅在两种藻类中发现的残留内共生核，隐生藻类和绿蛛形藻类，它们被研究用于模拟将内共生藻类整合到宿主控制的质体（细胞器发生）的进化过程。然而，过去的研究表明，在隐生植物和chlorararniophytes中，DNA从内共生体向宿主细胞核的转移已经停止，这意味着在遗传水平上，这两个系统已经完成了细胞器发生。此外，我们还没有确定被祖先绿蛛或隐藻吞没的内共生藻类最近的自由生活亲属，这使得很难推断器官发生如何改变内共生基因组。为了解决上述问题，我们需要新的具有核形的藻类，在这些藻类中，内共生体到宿主的DNA转移正在进行，并且可以在精细的分类尺度上推断内共生体/质体的起源。在这里，我们报道了两种以前描述过的鞭毛藻，菌株MGD和TGD，绿藻内共生体包裹着质体和残核（核形）。我们提供了DNA存在于两个核形和内共生基因转移到宿主（鞭毛藻）基因组的证据。此外，在MGD和TGD系统中，宿主和内共生体细胞核之间的DNA转移被发现正在进行。系统发育分析成功地在属水平上解决了内共生体的起源。综合这些证据，我们得出结论，MGD/TGD的宿主-内共生体整合不如隐生植物/色蛛纲植物，并提出这两种鞭毛藻作为解释器官发生的模型。
Nucleomorphs are relic endosymbiont nuclei so far found only in two algal groups, cryptophytes and chlorarachniophytes, which have been studied to model the evolutionary process of integrating an endosymbiont alga into a host-governed plastid (organellogenesis). However, past studies suggest that DNA transfer from the endosymbiont to host nuclei had already ceased in both cryptophytes and chlorarachniophytes, implying that the organellogenesis at the genetic level has been completed in the two systems. Moreover, we have yet to pinpoint the closest free-living relative of the endosymbiotic alga engulfed by the ancestral chlorarachniophyte or cryptophyte, making it difficult to infer how organellogenesis altered the endosymbiont genome. To counter the above issues, we need novel nucleomorph-bearing algae, in which endosymbiont-to-host DNA transfer is on-going and for which endosymbiont/plastid origins can be inferred at a fine taxonomic scale. Here, we report two previously undescribed dinoflagellates, strains MGD and TGD, with green algal endosymbionts enclosing plastids as well as relic nuclei (nucleomorphs). We provide evidence for the presence of DNA in the two nucleomorphs and the transfer of endosymbiont genes to the host (dinoflagellate) genomes. Furthermore, DNA transfer between the host and endosymbiont nuclei was found to be in progress in both the MGD and TGD systems. Phylogenetic analyses successfully resolved the origins of the endosymbionts at the genus level. With the combined evidence, we conclude that the host–endosymbiont integration in MGD/TGD is less advanced than that in cryptophytes/chrorarachniophytes, and propose the two dinoflagellates as models for elucidating organellogenesis.