Deciphering pathways of chloroplast and mitochondrial genome evolution in green algae

所有真核细胞都以含有DNA的膜结合细胞器为特征，称为线粒体和(在藻类和陆地植物中)叶绿体。通过研究这些与能量产生有关的重要细胞成分中编码的基因，研究人员发现，在包括绿藻和陆地植物在内的几个真核生物谱系中，叶绿体(Cp)和线粒体(Mt)基因组在大小、结构、基因含量、基因顺序和内含子含量方面表现出相当大的多样性。我们小组正在测定和分析绿藻细胞器基因组的完整序列，其大小从20,000到350,000个碱基不等。所有活着的绿色植物(绿藻纲)分为两个门：绿藻门和链藻门，绿藻门是绿藻的主体，链藻门是轮藻纲绿藻和所有陆地植物的组成部分。我们最近发现，cp基因组在链藻纲中的进化比在绿藻中保守得多，而且陆地植物的cp基因组继承了其轮藻绿藻祖先的许多特征。相反，在叶绿藻和链藻的进化过程中，mt基因组都发生了根本性的变化，陆地植物mtDNA似乎只遗传了轮藻绿藻的一些结构特征。拟议研究的目的有两个：(1)了解链藻和绿藻细胞器基因组是如何随着进化时间的推移而分化的；(2)解决生命树中有问题的绿藻谱系的分支顺序。来自不同绿藻谱系代表的完整cpDNA和mtDNA序列将被确定、解码，并与它们之前测得的绿色植物同源物进行比较。使用从整个细胞器基因组推断的系统发育框架，我们将重建基因丢失、基因重排和内含子获得/丢失的情景。所获得的信息将帮助我们破译形成细胞器基因组的力量。这些信息对于理解绿藻是如何进化并培育出陆地植物也是至关重要的。我们预计，拟议的研究将代表加拿大在细胞器基因组学领域的重大贡献。

All eukaryotic cells feature membrane-bound organelles containing DNA, called mitochondria and (in algae and land plants) chloroplasts. By studying the genes encoded in these vital cellular components involved in energy production, researchers have found that in several eukaryotic lineages, including green algae and land plants, the chloroplast (cp) and mitochondrial (mt) genomes exhibit considerable diversity in size, structure, gene content, gene order and intron content. Our group is determining and analyzing the complete sequences of organelle genomes from green algae, which range in size from 20,000 to 350,000 bases. All living green plants (Viridiplantae) are divided into two phyla: the Chlorophyta, comprising the bulk of the green algae, and the Streptophyta, comprising the green algae from the class Charophyceae and all land plants. We have recently shown that the cp genome is evolving much more conservatively in the Streptophyta than in the Chlorophyta and that the cp genome of land plants inherited a myriad of traits from their charophycean green algal ancestors. In contrast, the mt genome sustained radical changes during the evolution of both chlorophytes and streptophytes and it appears that land plant mtDNAs inherited only a few structural characters from charophycean green algae. The aims of the proposed research are two-fold: (1) to understand how streptophyte and chlorophyte organelle genomes diverged over evolutionary time and (2) to resolve the branching order of problematic green algal lineages in the tree of life. Complete cpDNA and mtDNA sequences from representatives of various green algal lineages will be determined, decoded, and compared to their previously sequenced green plant homologs. Using a phylogenic framework inferred from whole organelle genomes, we will be reconstruct scenarios of gene losses, gene rearrangements and intron gains/losses. The information gained will help us to decipher the forces that shape organelle genomes. This information is also crucial for understanding how green algae evolved and gave rise to land plants. We expect that the proposed studies will represent a major Canadian contribution in the area of organelle genomics.