Department of Biological Geological and Environmental Sciences, University of Bologna, Via Selmi, 3, Bologna 40126, Italy.
BMC Genomics. 2013 Jun 18;14:409. doi: 10.1186/1471-2164-14-409.
Bivalve mitochondrial genomes exhibit a wide array of uncommon features, like extensive gene rearrangements, large sizes, and unusual ways of inheritance. Species pertaining to the order Solemyida (subclass Opponobranchia) show many peculiar evolutionary adaptations, f.i. extensive symbiosis with chemoautotrophic bacteria. Despite Opponobranchia are central in bivalve phylogeny, being considered the sister group of all Autobranchia, a complete mitochondrial genome has not been sequenced yet.
In this paper, we characterized the complete mitochondrial genome of the Atlantic awning clam Solemya velum: A-T content, gene arrangement and other features are more similar to putative ancestral mollusks than to other bivalves. Two supranumerary open reading frames are present in a large, otherwise unassigned, region, while the origin of replication could be located in a region upstream to the cox3 gene.
We show that S. velum mitogenome retains most of the ancestral conchiferan features, which is unusual among bivalve mollusks, and we discuss main peculiarities of this first example of an organellar genome coming from the subclass Opponobranchia. Mitochondrial genomes of Solemya (for bivalves) and Haliotis (for gastropods) seem to retain the original condition of mollusks, as most probably exemplified by Katharina.
双壳类动物的线粒体基因组表现出广泛的非常见特征，如广泛的基因重排、较大的大小和不寻常的遗传方式。属于 Solemyida 目（Opponobranchia 亚纲）的物种表现出许多特殊的进化适应，例如与化能自养细菌的广泛共生。尽管 Opponobranchia 在双壳类动物的系统发育中处于中心地位，被认为是所有 Autobranchia 的姐妹群，但尚未对其完整的线粒体基因组进行测序。
在本文中，我们对大西洋遮阳蛤 Solemya velum 的完整线粒体基因组进行了表征：A-T 含量、基因排列和其他特征与假定的祖贝类动物更相似，而与其他双壳类动物则不相似。在一个大的、未分配的区域中存在两个超额外的开放阅读框，而复制起点可能位于 cox3 基因上游的区域。
我们表明，S. velum 的线粒体基因组保留了大多数祖贝类动物的特征，这在双壳类动物中是不常见的，我们讨论了这个来自 Opponobranchia 亚纲的第一个细胞器基因组的主要特征。Solemya（双壳类）和 Haliotis（腹足类）的线粒体基因组似乎保留了贝类的原始状态，这在 Katharina 中得到了很好的例证。
