Analysis of organellar genomes in brown algae reveals an independent introduction of similar foreign sequences into the mitochondrial genome.

Kelp species (Laminariales, Phaeophyceae) are globally widespread along temperate to Polar rocky coastal lines. Here we analyse the mitochondrial and chloroplast genomes of Laminaria rodriguezii , in comparison to the organellar genomes of other kelp species. We also provide the complete mitochondrial genome sequence of another endemic kelp species from a Polar habitat, the Arctic Laminaria solidungula. We compare phylogenetic trees derived from twenty complete mitochondrial and seven complete chloroplast kelp genomes. Interestingly, we found a stretch of more than 700 bp in the mitochondrial genome of L.rodriguezii , which is not present in any other yet sequenced member of the Phaeophyceae. This stretch matches a protein coding region in the mitochondrial genome from Desmarestia viridis , another brown seaweed. Their high similarity suggests that these sequences originated through independent introduction into the two species. Their origin could have been by infection by yet unknown similar mitoviruses, currently only known from fungi and plants. • We present three newly sequenced organellar genomes from the kelp species Laminaria rodriguezii and Laminaria solidungula. • Their specific features and phylogenetic information content is analysed and compared to other kelp organellar genomes. • Collinearity of the organellar genomes within the kelps make them apt as robust phylogenetic markers for the entire order. • We found an independent introduction of homologous nucleotide sequences into two brown algal mitochondrial genomes. • Their potential mitovirus origin is unprecedented and should be the beginning of endeavours to search for similar sequences. [ABSTRACT FROM AUTHOR]