Multiple losses of photosynthesis in Nitzschia (Bacillariophyceae) |
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| Authors: | Ryoma Kamikawa Naoji Yubuki Masaki Yoshida Misaka Taira Noriaki Nakamura Ken‐ichiro Ishida Brian S Leander Hideaki Miyashita Tetsuo Hashimoto Shigeki Mayama Yuji Inagaki |
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| Affiliation: | 1. Graduate School of Global Environmental Studies, Kyoto University, Kyoto, Japan;2. Graduate School of Human and Environmental Studies, Kyoto University, Kyoto, Japan;3. Departments of Zoology and Botany, University of British Columbia, Vancouver, British Columbia, Canada;4. Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Japan;5. Department of Biology, Tokyo Gakugei University, Tokyo, Japan;6. Center for Computational Sciences, University of Tsukuba, Tsukuba, Japan |
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| Abstract: | In order to obtain insights into the evolution of colorless (apochlorotic) diatoms, we investigated newly established apochlorotic strains of Nitzschia spp. using light and electron microscopy and molecular phylogenetic analyses. Fluorescence microscopic observations demonstrated that the apochlorotic diatoms lack chlorophylls. Transmission electron microscopy of two apochlorotic strains also demonstrated that their plastids lacked thylakoids; instead, having four‐membrane‐bound organelles without thylakoids, similar to nonphotosynthetic plastid remnants. From the apochlorotic strains, we also found plastid small subunit rRNA genes that were unusually long branched in phylogenetic analyses, as observed in other nonphotosynthetic plastids. Molecular phylogenetic analysis of the nucleus‐encoded large subunit rRNA genes showed eight distinct lineages for apochlorotic diatoms. The eight apochlorotic lineages were not monophyletic, suggesting that the loss of photosynthesis took place multiple times independently within Nitzschia. Several diatoms, including Nitzschia spp., are mixotrophic, which is an expected mode of nutrition that would help explain the evolutionary switch from a photosynthetic lifestyle to a heterotrophic lifestyle. |
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| Keywords: | apochlorotic diatoms genetic diversity large subunit rRNA molecular phylogenetic analysis nonphotosynthetic plastids plastid 16S rRNA |
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