Cyanobacteria and the Great Oxidation Event: evidence from genes and fossils.
Cyanobacteria and the Great Oxidation Event: evidence from genes and fossils.
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DOI：
10.1111/pala.12178
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发表时间：
2015-09
期刊：
影响因子：
2.6
通讯作者：
Donoghue PC
中科院分区：
文献类型：
--
作者：
Schirrmeister BE;Gugger M;Donoghue PC
蓝藻是最古老的进化谱系之一，从游离氧水平来看，产氧光合作用可能起源于3.0Ga之前。在整个前寒武纪，蓝藻是生物创新的最重要驱动力之一，对早期地球环境产生了强烈影响。在太古宙末期，它们导致了地球大气层的快速氧化，这一事件被称为大氧化事件(GOE)。然而，对早期蓝藻类群的起源和多样性知之甚少，原因是：(1)前寒武纪化石沉积物稀少；(2)分类群识别特征有限；(3)古代微化石保存不良。先前基于16S rRNA的研究表明，蓝藻中多细胞的起源可能与GOE有关。然而，单基因分析有其局限性，特别是对于深分支。我们使用基因组规模数据重建了蓝藻的进化史，并重新评估了前寒武纪化石记录，以获得更精确的校准，以便进行轻松的时钟分析。对于系统基因组的重建，我们在65个蓝藻分类群中鉴定了756个保守的基因序列，其中8个基因组已经被测序。基于最大似然和贝叶斯系统发育推断的特征状态重建证实了先前的发现，即大多数现代蓝藻的祖先是古老的多细胞蓝藻谱系。松弛的时钟分析为太古宙蓝藻的起源提供了坚实的支持，并在GOE之前向多细胞过渡。很可能多细胞对蓝藻的适合度和丰度的影响比先前假设的更大。多细胞作为一项重大的进化创新，形成了一个可供选择的新单位，可能有助于克服进化限制，使今天在蓝藻中看到的各种形态类型多样化。
Cyanobacteria are among the most ancient of evolutionary lineages, oxygenic photosynthesizers that may have originated before 3.0 Ga, as evidenced by free oxygen levels. Throughout the Precambrian, cyanobacteria were one of the most important drivers of biological innovations, strongly impacting early Earth's environments. At the end of the Archean Eon, they were responsible for the rapid oxygenation of Earth's atmosphere during an episode referred to as the Great Oxidation Event (GOE). However, little is known about the origin and diversity of early cyanobacterial taxa, due to: (1) the scarceness of Precambrian fossil deposits; (2) limited characteristics for the identification of taxa; and (3) the poor preservation of ancient microfossils. Previous studies based on 16S rRNA have suggested that the origin of multicellularity within cyanobacteria might have been associated with the GOE. However, single‐gene analyses have limitations, particularly for deep branches. We reconstructed the evolutionary history of cyanobacteria using genome scale data and re‐evaluated the Precambrian fossil record to get more precise calibrations for a relaxed clock analysis. For the phylogenomic reconstructions, we identified 756 conserved gene sequences in 65 cyanobacterial taxa, of which eight genomes have been sequenced in this study. Character state reconstructions based on maximum likelihood and Bayesian phylogenetic inference confirm previous findings, of an ancient multicellular cyanobacterial lineage ancestral to the majority of modern cyanobacteria. Relaxed clock analyses provide firm support for an origin of cyanobacteria in the Archean and a transition to multicellularity before the GOE. It is likely that multicellularity had a greater impact on cyanobacterial fitness and thus abundance, than previously assumed. Multicellularity, as a major evolutionary innovation, forming a novel unit for selection to act upon, may have served to overcome evolutionary constraints and enabled diversification of the variety of morphotypes seen in cyanobacteria today.