Unraveling the evolutionary history of the green algae and their genomes

揭开绿藻及其基因组的进化史

• 批准号: RGPIN-2017-04506
• 负责人: Lemieux, Claude
• 金额: $ 2.04万
• 依托单位: Université Laval
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2018
• 资助国家: 加拿大
• 起止时间: 2018-01-01 至 2019-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=657183
• 关键词: Unraveling; evolutionary; history; green; algae

The green algae represent one of the most successful groups of photosynthetic eukaryotes, but surprisingly little is known about their evolutionary history. About 450-500 million years ago (mya), a subset of freshwater green algae gave rise to the first land plants. Together with the land plants, green algae constitute the so-called green lineage or Viridiplantae. The Viridiplantae comprises 2 divisions: the Chlorophyta, containing the majority of the green algae, and the Streptophyta, containing all land plants and their closest green algal relatives, known as charophytes.*** Knowledge about the positions of the diverse green algal groups in the tree of life is essential for identifying the innovations underlying their remarkable adaptations to different environments. To decipher the phylogenetic relationships among major green algal lineages, my research team has been analyzing the genomes found in the chloroplasts and mitochondria. As a matter of fact, we have pioneered this comparative genomic approach for the study of green algae. We have shown that the chloroplast (cp) genome is a useful source of data for phylogenetic inference and that, contrary to what has been observed for land plants, it underwent tremendous changes during green algal diversification. The rRNA operon-encoding inverted repeat (IR) – a hallmark of the cp genome – experienced multiple waves of expansion/contraction and numerous losses in green algae; however, despite the suggested functional importance of the IR, the mechanism(s) underlying IR loss remain unclear.*** This proposal addresses fundamental issues on the evolution of chlorophytes and their genomes. To achieve 3 of the 4 delineated objectives, cp genomes of taxa from 3 distinct evolutionary nodes will be investigated. One of these objectives is to better understand the roles and properties of the IR along with the mechanisms of IR loss; the proposed analyses are based on our recent findings that the 2 IR copies diverged in sequence in 3 lineages of the Ulvophyceae and that this unprecedented discovery is compatible with a novel model of IR loss we proposed for the Ulotrichales. In another innovative line of inquiry, we plan to study the nuclear genome architectures of 2 prasinophytes from the lineage presumed to be sister to all core chlorophytes (the so-called clade VII); the goals are to gain insights into the biology of these algae and into the genomic changes that occurred during the transition from prasinophytes to core chlorophytes about 900 mya. These large-scale genomic studies are also likely to advance knowledge about algal adaptation to high salinity.*** The proposed research will provide high-quality training opportunities for graduate and undergraduate students in the areas of genomics and bioinformatics. Because these fields of science have multiple application domains, the proposal is expected to contribute to the economic and societal health of Canada.

绿藻代表了最成功的光合真核生物群体之一，但令人惊讶的是，人们对它们的进化史知之甚少。大约4.5 -5亿年前，淡水绿藻的一个子集产生了第一批陆地植物。绿藻与陆地植物一起构成了所谓的绿色谱系或绿绿植物。绿藻门包括两个部分：绿藻门，包含大部分的绿藻；链藻门，包含所有的陆地植物和它们最接近的绿藻亲戚，被称为绿藻。***了解不同绿藻群在生命之树上的位置，对于确定它们对不同环境的显著适应背后的创新是必不可少的。为了破译主要绿藻谱系之间的系统发育关系，我的研究小组一直在分析叶绿体和线粒体中发现的基因组。事实上，我们已经率先采用比较基因组的方法来研究绿藻。我们已经证明叶绿体（cp）基因组是系统发育推断的有用数据来源，并且与在陆地植物中观察到的相反，它在绿藻多样化过程中经历了巨大的变化。rRNA操纵子编码反转重复序列（IR）是cp基因组的标志，在绿藻中经历了多次扩张/收缩和大量损失；然而，尽管认为IR具有重要的功能，但IR丧失的机制仍不清楚。***这一建议解决了关于绿藻及其基因组进化的基本问题。为了实现4个目标中的3个，将研究来自3个不同进化节点的分类群的cp基因组。其中一个目标是更好地了解红外光谱的作用和性质以及红外光谱损失的机制；我们提出的分析是基于我们最近的发现，即在Ulvophyceae的3个谱系中，2个IR拷贝在序列上是不同的，这一前所未有的发现与我们为Ulotrichales提出的一个新的IR丢失模型是一致的。在另一个创新的研究方向上，我们计划研究被认为是所有核心绿藻的姐妹谱系（所谓的进化枝VII）的2种裸生植物的核基因组结构；目标是深入了解这些藻类的生物学特性，以及大约900万年前从原生植物向核心绿藻过渡期间发生的基因组变化。这些大规模的基因组研究也可能促进对藻类适应高盐度的认识。***拟议的研究将为基因组学和生物信息学领域的研究生和本科生提供高质量的培训机会。由于这些科学领域有多个应用领域，预计该提案将有助于加拿大的经济和社会健康。