The Origin of Plants: Genomes, rocks, and biogeochemical cycles.

毫无疑问，早期的陆地植物进化改变了地球，但我们对这一过程是如何发生的，我们的认识是混乱的。陆地植物化石首次出现的明显巧合与大气中氧气和二氧化碳的形成变化是早期陆地岩石缺失的产物，而弄清陆地植物体表组装的时间及其对全球生物地球化学循环的影响，需要对早期陆地植物演化及其影响的时间尺度有新的理解。早期陆地上的生命主要是微生物，但在大约7亿到4.2亿年前的某个时候，植物从水中迁移到陆地上。这个时间框架是有争议的，就目前的理解来说，它是非常宽泛的，但更准确地了解这些事件是将植物生命的早期进化与重大环境变化联系起来的关键。模棱两可和不确定性的出现是因为证据的主线相互冲突。化石，特别是植物微化石(孢子)，指出大约470 Ma(百万年前)开始的殖民，但早期孢子生产者的亲缘关系是有争议的。大型化石(植物茎、多细胞器官系统等)表明了较晚的殖民，大约开始于430 Ma。经过校准的分子系统学--基于分子序列数据对现存植物谱系分化的时间进行研究，利用化石对突变速度进行时间校准--指出陆地上生命的起源和早期进化可能始于新元古代晚期，比化石证据早很久。最近的研究已经确定了分子系统学和古生物学方法的困难，我们建议的研究计划将解决这一问题。我们已经组建了一个多学科团队来进行研究，以弥补这些不足。我们将基于基因组规模的分子序列数据(约1,000个基因，因此也就是约1,000,000个核苷酸)，建立一个强大的活植物谱系谱系。家谱将通过包括重要的和特殊保存的化石物种与时间联系起来。通过使用最先进的同步加速器计算机断层扫描对它们的解剖结构进行详细描述，这些将被正确放置，这是我们最近在一项概念验证研究中展示的一种新方法，提供了有价值的新数据。沉积体制已知会影响化石给出的年龄估计，因此我们还将应用我们开发的新方法来评估和修正这一点。总之，这些方法将使我们能够建立一个强大的系统发育图，以更精确的时间校准，我们将利用它来研究陆地植物关键器官和组织系统(如根、气孔、维管组织、叶)的进化组装及其对主要生物地球化学循环的影响。最后，我们将在全球生物地球化学循环(GENIE)的领先计算机模型中探索我们的植物进化时间尺度的含义。这将使我们能够产生对大气二氧化碳水平和有机碳生产率水平的预测，我们将根据地质观测进行测试。最终，我们将建立一个关于早期陆地植物进化的时间和节奏的新情景，陆地植物身体计划的集合，以及对这一事件对地球系统进化的影响的新理解。

There can be no doubt that early land plant evolution transformed the planet but how our knowledge of how this happened is in disarray. The clear coincidence in the first appearance of land plant fossils and formative shifts in atmospheric oxygen and CO2 is an artefact of the absence of earlier terrestrial rocks, and disentangling the timing of land plant bodyplan assembly and its impact on global biogeochemical cycles requires a new understanding of early land plant evolution and the timescale over which it was effected. Early life on land was mostly microbial, but sometime between about 700 million and 420 million years ago plants moved from water onto land. The timeframe is controversial and as currently understood it is very broad, but a more precise knowledge of the events is key to linking the early evolution of plant life to major environmental change. Ambiguity and uncertainty arise because the principal lines of evidence conflict. Fossils, notably plant microfossils (spores), point to colonization beginning about 470 Ma (million years ago), but the affinities of the early spore producers are controversial. Macrofossils (plant stems, multicellular organ systems, etc) indicate a later colonization, beginning about 430 Ma. Calibrated molecular phylogenies - studies of the timing of divergence of living plant lineages based on molecular sequence data, where the rate of mutation is calibrated to time using fossils - point to an origin and early evolution of life on land that may have begun during the Late Neoproterozoic, long predating the fossil evidence. Recent research has identified difficulties with both molecular phylogenetic and palaeontological approaches, which our proposed research program will address. We have assembled a multidisciplinary team to conduct research to remedy these shortcomings. We will establish a robust genealogy for living plant lineages based on a genome-scale amount of molecular sequence data (~1,000s genes and, therefore, ~1,000,000s nucleotides). The genealogy will be linked to time by including important and exceptionally preserved fossil species. These will be correctly placed through detailed characterization of their anatomy using state of the art Synchrotron Computed Tomography, a novel approach that we have recently shown to provide valuable new data in a recent proof of concept study. Sedimentary regime is known to affect the age estimate given by fossils, so we will also apply new methods develop by us to assess and to correct for this. Together, these approaches will enable us to develop a robust phylogeny calibrated with greater precision to time, which we will use to investigate the evolutionary assembly of key land plant organs and tissue systems (e.g., roots, stomata, vascular tissue, leaves) and their impact on major biogeochemical cycles. Finally, we will we will explore the implications of our plant evolutionary timescale within a leading computer model of global biogeochemical cycling (GENIE). This will enable us to generate predictions for levels of atmospheric carbon dioxide levels and of organic carbon productivity that we will test against geological observations. Ultimately, we will establish a new scenario for the timing and tempo of early land plant evolution, the assembly of land plant bodyplans, and a new understanding of the effect of this episode upon the evolution of the Earth System.