種子貯蔵タンパク質の小胞体からの輸送に関わるシロイヌナズナの新規因子 MAIGO2 Is Involved in Exit of Seed Storage Proteins from the Endoplasmic Reticulum in <I>Arabidopsis thaliana</I>

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Abstract

貯蔵タンパク質は種子の登熟期に小胞体で前駆体として大量に合成され,タンパク質蓄積型液胞に運ばれた後に,プロセシングを受けて成熟型に変換する.我々は,種子に貯蔵タンパク質の前駆体を異常に蓄積するシロイヌナズナ変異体(<I>maigo</I>)を単離・解析している (1).<I>maigo2</I> (<I>mag2</I>)変異体は貯蔵タンパク質の小胞体からの輸送に異常を示し,貯蔵タンパク質の前駆体を含む構造体を多数蓄積する (2).ショ糖密度勾配遠心法によりMAG2は小胞体膜上に局在することが判明した.MAG2はRINT-1/TIP20ドメインを持ち,小胞体局在型の2つのSNARE (At-Ufe1とAt-Sec20)と相互作用する.MAG2関連遺伝子(MAG2-related gene, MRG)のT-DNA挿入変異体は貯蔵タンパク質の前駆体を蓄積していた. MRG欠損変異体の種子細胞内には電子密度の高いコアを含む新規構造体が多数蓄積していた.以上の結果より,植物種子細胞においてMAG2タンパク質およびMRGタンパク質が貯蔵タンパク質の小胞体とゴルジ間の輸送に関与することが示唆された.<br> (1) Shimada et al. (2006) Plant Cell Physiol., 47(9): 1187-1194<br>(2) Li et al., Plant Cell (2006) in press.

Storage proteins are synthesized on ER as precursors and then are transported to protein storage vacuoles, where they are processed into mature forms. We isolated an <I>Arabidopsis</I> mutant (<I>mag2</I>) that accumulated precursors of 2S albumin and 12S globulin, in seeds (1). <I>mag2</I> seed cells contained many novel structures with an electron-dense core composed of the precursors of 2S albumin. 12S globulins were localized in the matrix region of the structures together with ER chaperones, BiP and PDI, which were more abundant in <I>mag2</I> seeds. MAG2 protein had a RINT-1/TIP20 domain in the C-terminal region. Some MAG2 molecules were peripherally associated with the ER membrane. MAG2 had an ability to bind to two ER-localized t-SNAREs (At-Sec20 and At-Ufe1). Our findings suggest that MAG2 functions in the transport of storage protein precursors between the ER and the Golgi complex.<br>(1) Li et al., Plant Cell (2006) in press.

Journal

  • Plant and Cell Physiology Supplement

    Plant and Cell Physiology Supplement 2007(0), 554-554, 2007

    The Japanese Society of Plant Physiologists

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