Smooth Loop-Like Mitochondrial Nucleus in the Primitive Red Alga <i>Cyanidioschyzon merolae</i> Revealed by Drying Treatment

  • Kuroiwa Tsuneyoshi
    Department of Chemical and Biological Science, Japan Women’s University
  • Yagisawa Fumi
    Center for Research Advancement and Collaboration, University of the Ryukyus
  • Fujiwara Takayuki
    Department of Gene Function and Phenomics, National Institute of Genetics
  • Misumi Osami
    Department of Biological Science and Chemistry, Faculty of Science, Yamaguchi University
  • Nagata Noriko
    Department of Chemical and Biological Science, Japan Women’s University
  • Imoto Yuuta
    Department of Cell Biology, Johns Hopkins University School of Medicine
  • Yoshida Yamato
    Department of Biological Sciences, Graduate School of Science, The University of Tokyo
  • Mogi Yuko
    Department of Biological Sciences, Graduate School of Science, The University of Tokyo
  • Miyagishima Shin-ya
    Department of Gene Function and Phenomics, National Institute of Genetics
  • Kuroiwa Haruko
    Department of Chemical and Biological Science, Japan Women’s University

Abstract

<p>It is thought that mitochondria were generated by the symbiosis of autonomous α-proteobacteria and a eukaryote-like organism derived from an archaeon of the species Sulfolobus. Soon after the symbiosis, most of the genome of the α-proteobacterium, which was required for autonomy, was lost. Many genes were transferred into the host genome. However, a small amount of DNA—the mitochondrial genome (mt-genome, mtDNA)—remained in the symbiotic organelle. The primitive eukaryotic cells increased the mtDNA copy number and formed a mitochondrial nucleus (mt-nucleus). The primitive unicellular eukaryote evolved into organisms with one mitochondrion containing multiple mtDNA copies per cell, and organisms with multiple mitochondria with a small number of mtDNA copies in each cell. There have been many studies on the mitochondria and mt-genomes of amoeba, plants, and animals which contain many mitochondria per cell, but only a few studies have reported morphological characteristics of the mitochondria and their genomes in primitive unicellular organisms that have only a single mitochondrion per cell. Here, we show that centrally located mt-nuclei in the primitive red alga Cyanidioschyzon merolae form smooth rings following the application of a drying method that produces slight cell swelling. We discuss regulatory mechanisms for genome function in endosymbiotic organelles on the basis of the differences between the copy number of mtDNA in smooth-ring shaped mt-nuclei and plastid DNA in bead-shaped plastid nuclei.</p>

Journal

  • CYTOLOGIA

    CYTOLOGIA 86 (1), 89-96, 2021-03-25

    Japan Mendel Society, International Society of Cytology

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