Li Libo, Wang Bin, Liu Yang, Qiu Yin-Long
Department of Ecology and Evolutionary Biology, The University Herbarium, University of Michigan, Ann Arbor, MI 48109-1048, USA.
J Mol Evol. 2009 Jun;68(6):665-78. doi: 10.1007/s00239-009-9240-7. Epub 2009 May 28.
Land plants possess some of the most unusual mitochondrial genomes among eukaryotes. However, in early land plants these genomes resemble those of green and red algae or early eukaryotes. The question of when during land plant evolution the dramatic change in mtDNAs occurred remains unanswered. Here we report the first completely sequenced mitochondrial genome of the hornwort, Megaceros aenigmaticus, a member of the sister group of vascular plants. It is a circular molecule of 184,908 base pairs, with 32 protein genes, 3 rRNA genes, 17 tRNA genes, and 30 group II introns. The genome contains many genes arranged in the same order as in those of a liverwort, a moss, several green and red algae, and Reclinomonas americana, an early-branching eukaryote with the most ancestral form of mtDNA. In particular, the gene order between mtDNAs of the hornwort and Physcomitrella patens (moss) differs by only 8 inversions and translocations. However, the hornwort mtDNA possesses 4 derived features relative to green alga mtDNAs--increased genome size, RNA editing, intron gains, and gene losses--which were all likely acquired during the origin and early evolution of land plants. Overall, this genome and those of other 2 bryophytes show that mitochondrial genomes in early land plants, unlike their seed plant counterparts, exhibit a mixed mode of conservative yet dynamic evolution.
陆地植物拥有真核生物中一些最不寻常的线粒体基因组。然而，在早期陆地植物中，这些基因组类似于绿藻、红藻或早期真核生物的基因组。陆地植物进化过程中，线粒体DNA何时发生巨大变化的问题仍未得到解答。在此，我们报告了角苔（Megaceros aenigmaticus）的首个完整测序的线粒体基因组，角苔是维管植物姐妹群的成员。它是一个由184,908个碱基对组成的环状分子，有32个蛋白质基因、3个rRNA基因、17个tRNA基因和30个II类内含子。该基因组包含许多基因，其排列顺序与地钱、苔藓、几种绿藻和红藻以及美洲隐滴虫（一种具有最原始线粒体DNA形式的早期分支真核生物）的相同。特别是，角苔和小立碗藓（苔藓）的线粒体DNA之间的基因顺序仅相差8次倒位和易位。然而，相对于绿藻线粒体DNA，角苔线粒体DNA具有4个衍生特征——基因组大小增加、RNA编辑、内含子增加和基因丢失——这些特征都可能是在陆地植物起源和早期进化过程中获得的。总体而言，这个基因组以及其他两种苔藓植物的基因组表明，早期陆地植物的线粒体基因组与其种子植物的线粒体基因组不同，呈现出保守但动态的混合进化模式。
