Principles of protein and lipid targeting in secondary symbiogenesis: Euglenoid, dinoflagellate, and sporozoan plastid origins and the eukaryote family tree
Principles of protein and lipid targeting in secondary symbiogenesis: Euglenoid, dinoflagellate, and sporozoan plastid origins and the eukaryote family tree
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DOI：
10.1111/j.1550-7408.1999.tb04614.x
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发表时间：
1999-07-01
影响因子：
2.2
通讯作者：
Cavalier-Smith, T
中科院分区：
文献类型：
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作者：
Cavalier-Smith, T
叶绿体进化中最大的未解决的问题是甲藻和裸藻叶绿体的起源，它们有三层膜而不是像植物和染色质那样有两层膜，以及孢子虫质体的起源，由四层光滑的膜包围。我回顾的证据表明，所有这三种原生动物的质体类型起源于真核内共生体的次生共生。而不是单独的共生事件，我认为，甲藻和孢子虫质体直接相关，甲藻和孢子虫的共同祖先是光合作用。我认为，最后共同祖先的所有泡状藻是光合作用，并获得了叶绿素c的质体在同一内共生事件的Chromista。Chromista和Alveolata被认为是一个分支，命名为chromalveolates。我认为，裸藻的质体来源于与绿蜘蛛相同的绿色藻类（可能是绿藻纲），而盘嵴藻纲（裸藻纲加过colozoa）和尾藻纲（包括绿蜘蛛纲）形成了一个分支，命名为cabozoa（具有叶绿素a + B的原生动物）。如果这两种理论都是正确的，那么在生命的历史中只有两个次级共生事件（由绿蜘蛛和隐藻核型体见证），而不是通常认为的七个。这大大减少了假设的叶绿体蛋白质靶向机制的独立起源和从内共生体到宿主细胞核的基因转移的数量。我讨论了膜和质体的损失和创新，这些理论所暗示的蛋白质靶向，他们的比较证据，以及他们对真核生物megaphylogeny的影响。进化保守主义的原则导致了一个新的理论，在膜生物发生的chlorarachneans和chromists和次生共生的关键步骤的质体周囊泡的功能。原生动物的分类也略有修订，放弃了可能是多系的放射足动物亚界，将有孔虫和放射虫归类为新的视网膜亚界，将太阳虫放入修订后的肉鞭毛虫亚界，在修订后的Eozoa亚界中为Jakobea加上Anaeromonadea建立了一个新的鞭毛虫门Loukozoa，并将Archezoa列为Eozoa中的亚界。
The biggest unsolved problems in chloroplast evolution are the origins of dinoflagellate and euglenoid chloroplasts, which have envelopes of three membranes not two like plants and chromists, and of the sporozoan plastid, bounded by four smooth membranes. I review evidence that all three of these protozoan plastid types originated by secondary symbiogenesis from eukaryotic endosymbionts. Instead of separate symbiogenetic events, I argue that dinoflagellate and sporozoan plastids are directly related and that the common ancestor of dinoflagellates and Sporozoa was photosynthetic. I suggest that the last common ancestor of all Alveolata was photosynthetic and acquired its chlorophyll c-containing plastids in the same endosymbiogenetic event as those of Chromista. Chromista and Alveolata are postulated to be a clade designated chromalveolates. I propose that euglenoids obtained their plastids from the same (possibly ulvophycean) green alga as chlorarachneans and that Discicristata (Euglenozoa plus Percolozoa) and Cercozoa (the group including chlorarachneans) form a clade designated cabozoa (protozoa with chlorophyll a + b). If both theories are correct, there were only two secondary symbiogenetic events (witnessed by the chlorarachnean and cryptomonad nucleomorphs) in the history of life, not seven as commonly assumed. This greatly reduces the postulated number of independent origins of chloroplast protein-targeting machinery and of gene transfers from endosymbiont to host nuclei. I discuss the membrane and plastid losses and innovations in protein targeting implied by these theories, the comparative evidence for them, and their implications for eukaryote megaphylogeny. The principle of evolutionary conservatism leads to a novel theory for the function of periplastid vesicles in membrane biogenesis of chlorarachneans and chromists and of the key steps in secondary symbiogenesis. Protozoan classification is also slightly revised by abandoning the probably polyphyletic infrakingdom Actinopoda, grouping Foraminifera and Radiolaria as a new infrakingdom Retaria, placing Heliozoa within a revised infrakingdom Sarcomastigota, establishing a new flagellate phylum Loukozoa for Jakobea plus Anaeromonadea within an emended subkingdom Eozoa, and ranking Archezoa as an infrakingdom within Eozoa.