Data from: Cyanobacteria and the Great Oxidation Event: evidence from genes and fossils

NOTE: PLEASE ALSO SEE THE CORRIGENDUM TO THE ORIGINAL ARTICLE, PUBLISHED AT http://dx.doi.org/10.1111/pala.12193. 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.注意：请同时参阅发表于http://dx.doi.org/10.1111/pala.12193的原文勘误表。蓝细菌（Cyanobacteria）是最为古老的演化支系之一，这类产氧光合生物可能早在30亿年（Ga）前便已起源，游离氧含量的相关证据可佐证这一推论。在整个前寒武纪时期，蓝细菌都是推动生物革新的核心驱动力之一，深刻影响了早期地球的环境格局。在太古宙（Archean Eon）末期，蓝细菌主导了地球大气快速氧化的事件——即“大氧化事件（Great Oxidation Event, GOE）”。 然而由于以下三方面的局限，学界对早期蓝细菌类群的起源与多样性仍所知有限：(1) 前寒武纪化石沉积稀缺；(2) 可用于类群鉴定的特征有限；(3) 古代微化石的保存状况极差。 既往基于16S rRNA的研究提出，蓝细菌的多细胞化起源或许与大氧化事件存在关联。但单基因分析存在固有局限，针对深层演化分支的分析这一问题尤为突出。本研究借助全基因组规模的数据重建了蓝细菌的演化历史，并重新评估了前寒武纪化石记录，旨在为宽松分子钟分析提供更为精准的校准参数。 在系统发育组学重建过程中，研究团队从65个蓝细菌类群中鉴定出756个保守基因序列，其中8个基因组为本研究首次完成测序。基于最大似然法与贝叶斯系统发育推演的性状状态重建结果，证实了既往研究结论：存在一个古老的多细胞蓝细菌支系，它是绝大多数现代蓝细菌的祖先类群。宽松分子钟分析有力支持了蓝细菌起源于太古宙，且其多细胞化发生在大氧化事件之前。 相较于此前的认知，多细胞化对蓝细菌适合度乃至种群丰度的提升作用可能更为显著。多细胞化作为一项关键演化创新，为自然选择提供了全新的作用单元，或许帮助蓝细菌突破了演化桎梏，并推动了现今蓝细菌多样形态类型的分化。