Origin of minicircular mitochondrial genomes in red algae

Eukaryotic organelle genomes are generally of conserved size and gene content within phylogenetic groups. However, significant variation in genome structure may occur. Here, we report that the Stylonematophyceae red algae contain multipartite circular mitochondrial genomes (i.e., minicircles) which encode one or two genes bounded by a specific cassette and a conserved constant region. These minicircles are visualized using Fluorescence Microscope and Scanning Electron Microscope, proving the circularity. Mitochondrial gene sets are reduced in these highly divergent mitogenomes. Newly generated chromosome-level nuclear genome assembly of Rhodosorus marinus reveals that most mitochondrial ribosomal subunit genes are transferred to the nuclear genome. Hetero-concatemers that resulted from recombination between minicircles and unique gene inventory that is responsible for mitochondrial genome stability may explain how the transition from typical mitochondrial genome to minicircles occurs. O..., Sample preparation
Culture strains of Tsunamia transpacifica JAW4874, Rufusia pilicola O7031, Stylonema alsidii JAW4424, Chroodactylon ornatum JAW4256, Chroothece mobilis SAG104.79, Rhodosorus marinus CCMP1338, and Bangiopsis subsimplex UTEX LB2854 were obtained from J.A. West (School of Biosciences 2, University of Melbourne, Parkville, Victoria 3010, Australia), F.D. Ott (905 NE Hilltop Drive, Topeka, Kansas 66617, USA), The Culture Collection of Algae at Göttingen University, Germany (SAG), The National Center for Marine Algae and Microbiota (NCMA), and the Culture Collection of Algae at The University of Texas at Austin, USA (UTEX), respectively. DY-V medium (added sea salt to 5 ppt) was used for culturing Rufusia pilicola. Chroothece mobilis and Chroodactylon ornatum were cultured in L1+DY-V (1:1 ratio) medium. The other samples were cultured in L1 medium. Culture flasks were kept under a white LED lamp (7.76 µmol photon m-2 s-1) at 20°C in a 12:12 light-dark cycle.
DNA and RNA ext...,