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Target of rapamycin (TOR) plays a critical role in triacylglycerol accumulation in microalgae

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Abstract

Most microalgae produce triacylglycerol (TAG) under stress conditions such as nitrogen depletion, but the underlying molecular mechanism remains unclear. In this study, we focused on the role of target of rapamycin (TOR) in TAG accumulation. TOR is a serine/threonine protein kinase that is highly conserved and plays pivotal roles in nitrogen and other signaling pathways in eukaryotes. We previously constructed a rapamycin-susceptible Cyanidioschyzon merolae, a unicellular red alga, by expressing yeast FKBP12 protein to evaluate the results of TOR inhibition (Imamura et al. in Biochem Biophys Res Commun 439:264–269, 2013). By using this strain, we here report that rapamycin-induced TOR inhibition results in accumulation of cytoplasmic lipid droplets containing TAG. Transcripts for TAG synthesis-related genes, such as glycerol-3-phosphate acyltransferase and acyl-CoA:diacylglycerol acyltransferase (DGAT), were increased by rapamycin treatment. We also found that fatty acid synthase-dependent de novo fatty acid synthesis was required for the accumulation of lipid droplets. Induction of TAG and up-regulation of DGAT gene expression by rapamycin were similarly observed in the unicellular green alga, Chlamydomonas reinhardtii. These results suggest the general involvement of TOR signaling in TAG accumulation in divergent microalgae.

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Acknowledgments

We thank Ms. A. Ishiwata and Dr. M. Iwai for their technical assistance and technical advice, respectively. This study was supported by the Ministry of Education, Culture, Sports, Science and Technology of Japan (Grants-in-Aid 22681010, 24117521, 25440129 and 26117711 to S.I. and Grants-in-Aid 24248061 to K.T.).

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Authors and Affiliations

  1. Chemical Resources Laboratory, Tokyo Institute of Technology, 4259-R1 Nagatsuta, Midori-ku, Yokohama, 226-8503, Japan

    Sousuke Imamura, Yasuko Kawase, Ikki Kobayashi, Toshiyuki Sone & Kan Tanaka

  2. Core Research for Evolutional Science and Technology (CREST), Japan Science and Technology Agency (JST), Saitama, 332-0012, Japan

    Sousuke Imamura, Atsuko Era, Shin-ya Miyagishima, Hiroyuki Ohta & Kan Tanaka

  3. Department of Cell Genetics, National Institute of Genetics, 1111 Yata, Mishima, Shizuoka, 411-8540, Japan

    Atsuko Era & Shin-ya Miyagishima

  4. Graduate School of Bioscience and Biotechnology, Tokyo Institute of Technology, 4259-B1 Nagatsuta, Midori-ku, Yokohama, 226-8501, Japan

    Mie Shimojima & Hiroyuki Ohta

  5. Earth-Life Science Institute, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo, 152-8551, Japan

    Hiroyuki Ohta

Authors
  1. Sousuke Imamura
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  2. Yasuko Kawase
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  3. Ikki Kobayashi
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  4. Toshiyuki Sone
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  7. Mie Shimojima
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  8. Hiroyuki Ohta
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  9. Kan Tanaka
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Correspondence to Sousuke Imamura or Kan Tanaka.

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Imamura, S., Kawase, Y., Kobayashi, I. et al. Target of rapamycin (TOR) plays a critical role in triacylglycerol accumulation in microalgae. Plant Mol Biol 89, 309–318 (2015). https://doi.org/10.1007/s11103-015-0370-6

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  • DOI: https://doi.org/10.1007/s11103-015-0370-6

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