1. Evolutionary significance of the ring-like plastid nucleus in the primitive red alga Cyanidioschyzon merolae as revealed by drying
- Author
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Tsuneyoshi Kuroiwa, Osami Misumi, Mio Ohnuma, Yuuta Imoto, Noriko Nagata, Fumi Yagisawa, and Haruko Kuroiwa
- Subjects
0106 biological sciences ,0301 basic medicine ,Lineage (evolution) ,macromolecular substances ,Plant Science ,Red algae ,01 natural sciences ,03 medical and health sciences ,chemistry.chemical_compound ,Algae ,Botany ,Plastids ,Plastid ,Cell Nucleus ,biology ,Cell Biology ,General Medicine ,biology.organism_classification ,Biological Evolution ,Brown algae ,030104 developmental biology ,Cyanidioschyzon merolae ,chemistry ,Rhodophyta ,Green algae ,DNA ,010606 plant biology & botany - Abstract
Primary plastids originated from a free-living cyanobacterial ancestor and possess their own genomes-probably a few DNA copies. These genomes, which are organized in centrally located plastid nuclei (CN-type pt-nuclei), are produced from preexisting plastids by binary division. Ancestral algae with a CN-type pt-nucleus diverged and evolved into two basal eukaryotic lineages: red algae with circular (CL-type) pt-nuclei and green algae with scattered small (SN-type) pt-nuclei. Although the molecular dynamics of pt-nuclei in green algae and plants are now being analyzed, the process of the conversion of the original algae with a CN-type pt-nucleus to red algae with a CL-type one has not been studied. Here, we show that the CN-type pt-nucleus in the primitive red alga Cyanidioschyzon merolae can be changed to the CL-type by application of drying to produce slight cell swelling. This result implies that CN-type pt-nuclei are produced by compact packing of CL-type ones, which suggests that a C. merolae-like alga was the original progenitor of the red algal lineage. We also observed that the CL-type pt-nucleus has a chain-linked bead-like structure. Each bead is most likely a small unit of DNA, similar to CL-type pt-nuclei in brown algae. Our results thus suggest a C. merolae-like alga as the candidate for the secondary endosymbiont of brown algae.
- Published
- 2020