The Complete Sequence of the Mitochondrial Genome of <i>Butomus umbellatus</i> – A Member of an Early Branching Lineage of Monocotyledons

<div><p>In order to study the evolution of mitochondrial genomes in the early branching lineages of the monocotyledons, i.e., the Acorales and Alismatales, we are sequencing complete genomes from a suite of key taxa. As a starting point the present paper describes the mitochondrial genome of <i>Butomus umbellatus</i> (Butomaceae) based on next-generation sequencing data. The genome was assembled into a circular molecule, 450,826 bp in length. Coding sequences cover only 8.2% of the genome and include 28 protein coding genes, four rRNA genes, and 12 tRNA genes. Some of the tRNA genes and a 16S rRNA gene are transferred from the plastid genome. However, the total amount of recognized plastid sequences in the mitochondrial genome is only 1.5% and the amount of DNA transferred from the nucleus is also low. RNA editing is abundant and a total of 557 edited sites are predicted in the protein coding genes. Compared to the 40 angiosperm mitochondrial genomes sequenced to date, the GC content of the <i>Butomus</i> genome is uniquely high (49.1%). The overall similarity between the mitochondrial genomes of <i>Butomus</i> and <i>Spirodela</i> (Araceae), the closest relative yet sequenced, is low (less than 20%), and the two genomes differ in size by a factor 2. Gene order is also largely unconserved. However, based on its phylogenetic position within the core alismatids <i>Butomus</i> will serve as a good reference point for subsequent studies in the early branching lineages of the monocotyledons.</p>