title: Extensive Mitochondrial mRNA Editing and Unusual Mitochondrial Genome Organization in Calcaronean Sponges.
abstract: One of the unusual features of DNA-containing organelles in general and mitochondria in particular is the frequent occurrence of RNA editing [1]. The term "RNA editing" refers to a variety of mechanistically unrelated biochemical processes that alter RNA sequence during or after transcription [2]. The editing can be insertional, deletional, or substitutional and has been found in all major types of RNAs [3, 4]. Although mitochondrial mRNA editing is widespread in some eukaryotic lineages [5-7], it is rare in animals, with reported cases limited both in their scope and in phylogenetic distribution [8-11] (see also [12]). While analyzing genomic data from calcaronean sponges Sycon ciliatum and Leucosolenia complicata, we were perplexed by the lack of recognizable mitochondrial coding sequences. Comparison of genomic and transcriptomic data from these species revealed the presence of mitochondrial cryptogenes whose transcripts undergo extensive editing. This editing consisted of single or double uridylate (U) insertions in pre-existing short poly(U) tracts. Subsequent analysis revealed the presence of similar editing in Sycon coactum and the loss of editing in Petrobiona massiliana, a hypercalcified calcaronean sponge. In addition, mitochondrial genomes of at least some calcaronean sponges were found to have a highly unusual architecture, with nearly all genes located on individual and likely linear chromosomes. Phylogenetic analysis of mitochondrial coding sequences revealed accelerated rates of sequence evolution in this group. The latter observation presents a challenge for the mutational-hazard hypothesis [13], which posits that mRNA editing should not occur in lineages with an elevated mutation rate.
authors.affiliation: Department of Ecology, Evolution, and Organismal Biology, Iowa State University, 251 Bessey Hall, Ames, IA 50011, USA. Electronic address: dlavrov@iastate.edu.
authors.forename: Dennis V
authors.initials: DV
authors.lastname: Lavrov
authors.affiliation: Sars International Centre for Marine Molecular Biology, University of Bergen, Thormøhlensgate 55, 5008 Bergen, Norway.
authors.forename: Marcin
authors.initials: M
authors.lastname: Adamski
authors.affiliation: Institut Méditerranéen de Biodiversité et d'Ecologie Marine et Continentale, UMR CNRS, IRD, Aix Marseille Université, Avignon Université, Station Marine d'Endoume, Rue Batterie des Lions, 13007 Marseille, France.
authors.forename: Pierre
authors.initials: P
authors.lastname: Chevaldonné
authors.affiliation: Sars International Centre for Marine Molecular Biology, University of Bergen, Thormøhlensgate 55, 5008 Bergen, Norway.
authors.forename: Maja
authors.initials: M
authors.lastname: Adamska
mesh_terms: D000818:Animals; D001483:Base Sequence; D005075:Biological Evolution; D004272:DNA, Mitochondrial / Q000235:genetics* / Q000378:metabolism; D054629:Genome, Mitochondrial; D008928:Mitochondria / Q000235:genetics* / Q000378:metabolism*; D008969:Molecular Sequence Data; D059645:Mutation Rate; D010802:Phylogeny; D011161:Porifera / Q000235:genetics*; D012313:RNA / Q000235:genetics / Q000378:metabolism; D017393:RNA Editing; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism
chemical_list: D004272:DNA, Mitochondrial; D012333:RNA, Messenger; D012313:RNA