MAG2 and three MAG2-INTERACTING PROTEINs form an ER-localized complex to facilitate storage protein transport in Arabidopsis thaliana

Authors

  • Lixin Li,

    1. Alkali Soil Natural Environmental Science Center, Key Laboratory of Saline–Alkali Vegetation Ecology Restoration in Oil Field (SAVER), Ministry of Education, Northeast Forestry University, Harbin, China
    2. Department of Botany, Graduate School of Science, Kyoto University, Kyoto, Japan
    3. College of Life Science, Northeast Forestry University, Harbin, China
    Search for more papers by this author
    • These authors contributed equally to this work.
  • Tomoo Shimada,

    1. Department of Botany, Graduate School of Science, Kyoto University, Kyoto, Japan
    Search for more papers by this author
    • These authors contributed equally to this work.
  • Hideyuki Takahashi,

    1. Department of Botany, Graduate School of Science, Kyoto University, Kyoto, Japan
    Current affiliation:
    1. School of Environmental Science and Engineering, Kochi University of Technology, Tosayamada, Kochi, Japan
    Search for more papers by this author
  • Yasuko Koumoto,

    1. Department of Botany, Graduate School of Science, Kyoto University, Kyoto, Japan
    Search for more papers by this author
  • Makoto Shirakawa,

    1. Department of Botany, Graduate School of Science, Kyoto University, Kyoto, Japan
    Search for more papers by this author
  • Junpei Takagi,

    1. Department of Botany, Graduate School of Science, Kyoto University, Kyoto, Japan
    Search for more papers by this author
  • Xiaonan Zhao,

    1. Alkali Soil Natural Environmental Science Center, Key Laboratory of Saline–Alkali Vegetation Ecology Restoration in Oil Field (SAVER), Ministry of Education, Northeast Forestry University, Harbin, China
    2. College of Life Science, Northeast Forestry University, Harbin, China
    Search for more papers by this author
  • Baoyu Tu,

    1. Alkali Soil Natural Environmental Science Center, Key Laboratory of Saline–Alkali Vegetation Ecology Restoration in Oil Field (SAVER), Ministry of Education, Northeast Forestry University, Harbin, China
    2. College of Life Science, Northeast Forestry University, Harbin, China
    Search for more papers by this author
  • Hongmin Jin,

    1. Alkali Soil Natural Environmental Science Center, Key Laboratory of Saline–Alkali Vegetation Ecology Restoration in Oil Field (SAVER), Ministry of Education, Northeast Forestry University, Harbin, China
    2. College of Life Science, Northeast Forestry University, Harbin, China
    Search for more papers by this author
  • Zhe Shen,

    1. Alkali Soil Natural Environmental Science Center, Key Laboratory of Saline–Alkali Vegetation Ecology Restoration in Oil Field (SAVER), Ministry of Education, Northeast Forestry University, Harbin, China
    Search for more papers by this author
  • Baoda Han,

    1. Alkali Soil Natural Environmental Science Center, Key Laboratory of Saline–Alkali Vegetation Ecology Restoration in Oil Field (SAVER), Ministry of Education, Northeast Forestry University, Harbin, China
    2. College of Life Science, Northeast Forestry University, Harbin, China
    Search for more papers by this author
  • Meihui Jia,

    1. Alkali Soil Natural Environmental Science Center, Key Laboratory of Saline–Alkali Vegetation Ecology Restoration in Oil Field (SAVER), Ministry of Education, Northeast Forestry University, Harbin, China
    2. College of Life Science, Northeast Forestry University, Harbin, China
    Search for more papers by this author
  • Maki Kondo,

    1. Department of Cell Biology, National Institute for Basic Biology, Okazaki, Japan
    Search for more papers by this author
  • Mikio Nishimura,

    1. Department of Cell Biology, National Institute for Basic Biology, Okazaki, Japan
    Search for more papers by this author
  • Ikuko Hara-Nishimura

    Corresponding author
    1. Department of Botany, Graduate School of Science, Kyoto University, Kyoto, Japan
    Search for more papers by this author

Summary

In Arabidopsis thaliana, MAIGO 2 (MAG2) is involved in protein transport between the endoplasmic reticulum (ER) and the Golgi apparatus via its association with the ER-localized t-SNARE components SYP81/AtUfe1 and SEC20. To characterize the molecular machinery of MAG2-mediated protein transport, we explored MAG2-interacting proteins using transgenic A. thaliana plants expressing TAP-tagged MAG2. We identified three proteins, which were designated as MAG2-INTERACTING PROTEIN 1–3 [MIP1 (At2g32900), MIP2 (At5g24350) and MIP3 (At2g42700)]. Both MIP1 and MAG2 localized to the ER membrane. All of the mag2, mip1, mip2 and mip3 mutants exhibited a defect in storage protein maturation, and developed abnormal storage protein body (MAG body) structures in the ER of seed cells. These observations suggest that MIPs are closely associated with MAG2 and function in protein transport between the ER and Golgi apparatus. MIP1 and MIP2 contain a Zeste–White 10 (ZW10) domain and a Sec39 domain, respectively, but have low sequence identities (21% and 23%) with respective human orthologs. These results suggest that the plant MAG2–MIP1–MIP2 complex is a counterpart of the triple-subunit tethering complexes in yeast (Tip20p–Dsl1p–Sec39p) and humans (RINT1–ZW10–NAG). Surprisingly, the plant complex also contained a fourth member (MIP3) with a Sec1 domain. There have been no previous reports showing that a Sec1-containing protein is a subunit of ER-localized tethering complexes. Our results suggest that MAG2 and the three MIP proteins form a unique complex on the ER that is responsible for efficient transport of seed storage proteins.

Ancillary