Abstract 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.

中文翻译：

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蓝藻和大氧化事件：来自基因和化石的证据

摘要 蓝藻是最古老的进化谱系之一，是产氧光合作用者，自由氧水平证明其可能起源于 3.0 Ga 之前。在整个前寒武纪时期，蓝藻是生物创新最重要的驱动力之一，对早期地球环境产生了强烈影响。在太古代末期，它们在被称为大氧化事件（GOE）的事件中导致了地球大气层的快速氧化。然而，由于以下原因，人们对早期蓝藻类群的起源和多样性知之甚少：（1）前寒武纪化石沉积的稀缺；(2) 分类单元识别的特征有限；(3)古代微体化石保存较差。先前基于 16S rRNA 的研究表明，蓝藻内多细胞性的起源可能与 GOE 有关。然而，单基因分析有局限性，特别是对于深层分支。我们使用基因组规模数据重建了蓝藻的进化历史，并重新评估了前寒武纪化石记录，以获得更精确的校准，以进行轻松的时钟分析。为了进行系统发育重建，我们在 65 个蓝藻类群中鉴定了 756 个保守基因序列，其中 8 个基因组已在本研究中进行了测序。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，即古代多细胞蓝藻谱系是大多数现代蓝藻的祖先。松弛时钟分析为太古代蓝藻的起源以及GOE之前向多细胞的过渡提供了坚定的支持。多细胞性对蓝藻适应性和丰度的影响可能比之前的假设更大。多细胞性作为一项主要的进化创新，形成了一种新的选择单元，可能有助于克服进化限制，并使当今蓝藻中看到的各种形态类型多样化。