Distinctive architecture of the chloroplast genome in the chlorophycean green alga Stigeoclonium helveticum
Distinctive architecture of the chloroplast genome in the chlorophycean green alga Stigeoclonium helveticum
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DOI：
10.1007/s00438-006-0156-2
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发表时间：
2006-11-01
影响因子：
3.1
通讯作者：
Turmel, Monique
中科院分区：
文献类型：
--
作者：
Belanger, Anne-Sophie;Brouard, Jean-Simon;Turmel, Monique
在叶绿藻的进化过程中，叶绿体基因组经历了许多结构变化，其中绿藻纲表现出最低程度的祖先特征。我们之前已经证明，莱茵衣藻目 (Chlamydomonadales) 和斜生栅藻 (Sphaeropleales) 的叶绿体 DNA (cpDNA) 的完整测序在基因顺序上彼此高度混乱。在这里，我们报告了第三绿藻谱系成员 Stigeoclonium helveticum（Chaetophorales）的完整 cpDNA 序列。该基因组编码 97 个基因并包含 21 个内含子（包括插入新位点的 4 个推定反式剪接的 II 组内含子），其派生特征非常丰富，并且相对于绿藻类基因组进行了极其重新排列。 Stigeoclonium cpDNA 长度为 223,902 bp，是迄今为止测序的最大叶绿体基因组，与衣藻和栅藻相比，其没有大的反向重复序列。有趣的是，DNA 链之间的基因分布模式和每条链的碱基组成偏差表明 Stigeoclonium 基因组从单一起点进行双向复制。与大多数已知的反式剪接组 II 内含子不同，Stigeoclonium 的反式剪接内含子在结构域 I 和 II 中表现出断裂。通过将我们的比较基因组分析置于系统发育框架中，我们推断出导致绿藻纲基因组结构变化的突变事件的进化情景。
The chloroplast genome has experienced many architectural changes during the evolution of chlorophyte green algae, with the class Chlorophyceae displaying the lowest degree of ancestral traits. We have previously shown that the completely sequenced chloroplast DNAs (cpDNAs) of Chamydomonas reinhardtii (Chlamydomonadales) and Scenedesmus obliquus (Sphaeropleales) are highly scrambled in gene order relative to one another. Here, we report the complete cpDNA sequence of Stigeoclonium helveticum (Chaetophorales), a member of a third chlorophycean lineage. This genome, which encodes 97 genes and contains 21 introns (including four putatively trans-spliced group II introns inserted at novel sites), is remarkably rich in derived features and extremely rearranged relative to its chlorophycean counterparts. At 223,902 bp, Stigeoclonium cpDNA is the largest chloroplast genome sequenced thus far, and in contrast to those of Chlamydomonas and Scenedesmus, features no large inverted repeat. Interestingly, the pattern of gene distribution between the DNA strands and the bias in base composition along each strand suggest that the Stigeoclonium genome replicates bidirectionally from a single origin. Unlike most known trans-spliced group II introns, those of Stigeoclonium exhibit breaks in domains I and II. By placing our comparative genome analyses in a phylogenetic framework, we inferred an evolutionary scenario of the mutational events that led to changes in genome architecture in the Chlorophyceae.