Gene arrangement convergence,diverse intron content, and genetic code modifications in mitochondrial genomes of sphaeropleales (chlorophyta)

Abstract

Themajority of our knowledge about mitochondrial genomes of Viridiplantae comes fromland plants, butmuch less is known about their green algal relatives. In the green algal order Sphaeropleales (Chlorophyta), only one representative mitochondrial genome is currently available - that of Acutodesmus obliquus. Our study adds nine completely sequenced and three partially sequenced mitochondrialgenomes spanningthephylogeneticdiversity ofSphaeropleales.We shownot only a size range of25-53 kband variation in intron content (0-11) andgene order but also conservation of 13core respiratory genes and fragmented ribosomal RNAgenes.We also report an unusual case of gene arrangement convergence in Neochloris aquatica,where the tworns fragments were secondarily placed in close proximity. Finally, we report the unprecedented usage of UCG as stop codon in Pseudomuriella schumacherensis. In addition, phylogenetic analyses of the mitochondrial protein-coding genes yield a fully resolved,well-supported phylogeny, showing promise for addressing systematic challenges in green algae.