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: 2020
• 资助国家: 加拿大
• 起止时间: 2020-01-01 至 2021-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=711085
• 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.

绿色藻类是最成功的光合真核生物之一，但令人惊讶的是，人们对它们的进化历史知之甚少。大约4.5亿至5亿年前（百万年），淡水绿色藻类的一个子集产生了第一批陆地植物。与陆地植物一起，绿色藻类构成了所谓的绿色谱系或绿色植物。绿色植物科包括两个部门：绿藻门，包含大多数的绿色藻类，和链藻门，包含所有的陆地植物和它们最接近的绿色藻类亲属，称为轮藻。 了解不同的绿色藻类群体在生命树中的位置，对于确定它们对不同环境的显著适应性的创新至关重要。为了破译主要绿色藻类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，我们已经开创了这种比较基因组方法用于绿色藻类的研究。我们已经表明，叶绿体（cp）基因组是一个有用的数据源系统发育推断，相反，已观察到的陆地植物，它经历了巨大的变化，在绿色藻类多样化。编码rRNA操纵子的反向重复序列（IR）是cp基因组的标志，在绿色藻类中经历了多波扩张/收缩和多次丢失;然而，尽管IR的功能重要性已得到证实，但IR丢失的潜在机制仍不清楚。 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个划定的目标中的3个，将研究来自3个不同进化节点的分类群的cp基因组。这些目标之一是为了更好地了解IR的作用和性质，沿着IR损失的机制;提出的分析是基于我们最近的发现，即2个IR拷贝在3个谱系的石莼纲中顺序发散，这一前所未有的发现与我们提出的Ulotrichales的IR损失的新模型是相容的。在另一个创新的调查路线中，我们计划研究2个prasinophytes的核基因组结构，这些基因组结构被认为是所有核心绿藻的姐妹（所谓的进化枝VII）;目标是深入了解这些藻类的生物学，以及在从prasinophytes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有可能推进关于藻类适应高盐度的知识。 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，该提案预计将有助于加拿大的经济和社会健康。