Dating the cyanobacterial ancestor of the chloroplast
Dating the cyanobacterial ancestor of the chloroplast
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DOI：
10.1038/ismej.2010.2
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发表时间：
2010-06-01
期刊：
影响因子：
11
通讯作者：
Castillo, Amanda
中科院分区：
文献类型：
--
作者：
Falcon, Luisa I.;Magallon, Susana;Castillo, Amanda
蓝藻在地球上的生命史上发挥了关键作用，它是第一批进行氧合光合作用的生物，它改变了大气化学，并允许好氧真核生物的进化。叶绿体是光自养真核生物的细胞器，光合作用的大部分发生在叶绿体中。尽管最初关于蓝藻是叶绿体祖先的说法受到了质疑，但这一观点现在已被广泛接受。在这里，我们试图利用系统发育分析和分子时钟来解析和确定叶绿体蓝藻的祖先。我们发现，叶绿体形成了一个单系谱系，与固定I、N-2亚节的单细胞蓝藻(色球藻目)关系最为密切，而异胞藻目蓝藻则是它们的姐妹群。古元古代出现了念珠目和变色球藻，中元古代出现了叶绿体。蓝藻固定N-2的能力可能只在太古代晚期和早元古代出现过一次。此外，我们还发现太古宙中可能存在放氧蓝藻。我们的结果表明，自由生活的蓝藻能够通过氧气固定二氧化碳来储存淀粉，并固定大气中的N-2，这将是一种非常重要的细胞内获取，正如今天从几条证据中可以描述的那样，它可能已经通过内共生成为叶绿体。《ISME期刊》(2010年)4777783；doi：10.1038/ismej.2010.2；2010年3月4日在线出版
Cyanobacteria have had a pivotal role in the history of life on Earth being the first organisms to perform oxygenic photosynthesis, which changed the atmospheric chemistry and allowed the evolution of aerobic Eukarya. Chloroplasts are the cellular organelles of photoautotrophic eukaryotes in which most portions of photosynthesis occur. Although the initial suggestion that cyanobacteria are the ancestors of chloroplasts was greeted with skepticism, the idea is now widely accepted. Here we attempt to resolve and date the cyanobacterial ancestry of the chloroplast using phylogenetic analysis and molecular clocks. We found that chloroplasts form a monophyletic lineage, are most closely related to subsection-I, N-2-fixing unicellular cyanobacteria (Order Chroococcales), and heterocyst-forming Order Nostocales cyanobacteria are their sister group. Nostocales and Chroococcales appeared during the Paleoproterozoic and chloroplasts appeared in the mid-Proterozoic. The capability of N-2 fixation in cyanobacteria may have appeared only once during the late Archaean and early Proterozoic eons. Furthermore, we found that oxygen-evolving cyanobacteria could have appeared in the Archaean. Our results suggest that a free- living cyanobacterium with the capacity to store starch through oxygenic CO2 fixation, and to fix atmospheric N-2, would be a very important intracellular acquisition, which, as can be recounted today from several lines of evidence, would have become the chloroplast by endosymbiosis. The ISME Journal (2010) 4, 777-783; doi:10.1038/ismej.2010.2; published online 4 March 2010