Department of Life Sciences, Graduate School of Arts and Sciences, University of Tokyo, Meguro-ku, Tokyo 153-8902, Japan.
Department of Life Sciences, Graduate School of Arts and Sciences, University of Tokyo, Meguro-ku, Tokyo 153-8902, Japan
Plant Physiol. 2018 Aug;177(4):1487-1497. doi: 10.1104/pp.18.00227. Epub 2018 Jun 26.
Angiosperms germinated in the dark develop etioplasts, the chloroplast precursors, in cotyledon cells. Etioplasts contain lattice membrane structures called prolamellar bodies (PLBs) and lamellar prothylakoids as internal membrane systems. PLBs accumulate the chlorophyll intermediate protochlorophyllide (Pchlide) in a complex with NADPH and light-dependent NADPH:Pchlide oxidoreductase (LPOR). Two galactolipids, monogalactosyldiacylglycerol and digalactosyldiacylglycerol (DGDG), are major constituents of etioplast membranes. We previously reported that monogalactosyldiacylglycerol facilitates the synthesis of Pchlide and the formation of the Pchlide-LPOR-NADPH complex in etioplasts, but the importance of DGDG in etioplasts is still unknown. To determine the role of DGDG in etioplast development and functions, we characterized a knockout mutant () of Arabidopsis () , which encodes the major isoform of DGDG synthase, in the etioplast development stage. In etiolated seedlings, DGDG content decreased to 20% of the wild-type level, the lattice structure of PLBs was disordered, and the development of prothylakoids was impaired. In addition, membrane-associated processes of Pchlide biosynthesis, formation of the Pchlide-LPOR-NADPH complex, and dissociation of the complex after the photoconversion of Pchlide to chlorophyllide were impaired in , although the photoconversion reaction by LPOR was not affected by the DGDG deficiency. Total carotenoid content also decreased in etiolated seedlings, but the carotenoid composition was unchanged. Our data demonstrate a deep involvement of DGDG in the formation of the internal membrane structures in etioplasts as well as in membrane-associated processes of pigment biosynthesis and pigment-protein complex organization.
被子植物在黑暗中萌发时，子叶细胞中会形成叶绿体前体——黄质体。黄质体含有晶格膜结构，称为前质体体（PLB）和类囊体前质体作为内部膜系统。PLB 以与 NADPH 和依赖光的 NADPH：Pchlide 氧化还原酶（LPOR）结合的叶绿素中间产物原叶绿素ide（Pchlide）的复合物形式积累。两种半乳糖脂，单半乳糖二酰基甘油和双半乳糖二酰基甘油（DGDG）是黄质体膜的主要成分。我们之前报道过，单半乳糖二酰基甘油有助于 Pchlide 的合成和 Pchlide-LPOR-NADPH 复合物在黄质体中的形成，但 DGDG 在黄质体中的重要性仍不清楚。为了确定 DGDG 在黄质体发育和功能中的作用，我们对拟南芥（Arabidopsis）的一个缺失突变体（）进行了表征，该基因编码 DGDG 合酶的主要同工型，在黄质体发育阶段。在黄化的幼苗中，DGDG 含量下降到野生型水平的 20%，PLB 的晶格结构紊乱，前质体的发育受到损害。此外，在中，尽管 LPOR 的光转化反应不受 DGDG 缺乏的影响，但 Pchlide 生物合成的膜相关过程、Pchlide-LPOR-NADPH 复合物的形成以及 Pchlide 向叶绿素ide 的光转化后的复合物解离都受到了损害。总类胡萝卜素含量也在黄化的幼苗中下降，但类胡萝卜素组成没有变化。我们的数据表明，DGDG 深度参与了黄质体内部膜结构的形成以及与色素生物合成和色素蛋白复合物组织相关的膜相关过程。
