School of Mechanical and Aerospace Engineering, Nanyang Technological University, Singapore 639798, Republic of Singapore.
Department of Molecular Metabolism, Harvard T. H. Chan School of Public Health, Boston MA 02115, USA.
Plant Physiol. 2022 Jan 20;188(1):526-539. doi: 10.1093/plphys/kiab512.
Dehydration damages the structural integrity of the chloroplast membrane and, consequently, the normal photosynthetic function of this organelle. Remodeling of galactolipids by converting monogalactosyl-diacylglycerol (MGDG) to digalactosyl-diacylglycerol (DGDG) and oligo-galactolipids is an effective adaptation strategy for protecting against dehydration damage to the chloroplast membrane. However, detailed molecular mechanisms are missing. In this study, by performing molecular-level simulations of bi-lamellar membranes under various dehydration conditions, we find that MGDG-to-DGDG remodeling protects the chloroplast membrane in a unique manner by simultaneously dictating both the extent and the pattern of fusion stalks formed with the apposed membrane. Specifically, MGDG-rich membranes form elongated stalks at a moderate dehydration level, whereas DGDG-rich membranes form smaller, rounded stalks. Simulations of wild-type and mutant Arabidopsis (Arabidopsis thaliana) outer chloroplast membranes further confirm that the mutant membrane without galactolipid remodeling is more susceptible to membrane fusion due to its higher MGDG content. Our work reveals the underlying physical mechanisms that govern the pattern and extent of membrane fusion structures, paving the way for rational genetic engineering of crops with improved dehydration tolerance.
脱水会破坏叶绿体膜的结构完整性，从而影响该细胞器的正常光合作用功能。通过将单半乳糖基二酰基甘油 (MGDG) 转化为双半乳糖基二酰基甘油 (DGDG) 和寡半乳糖脂来重塑半乳糖脂是一种有效的适应策略，可以防止叶绿体膜因脱水而受损。然而，其中的详细分子机制尚不清楚。在这项研究中，通过对不同脱水条件下双层膜进行分子水平模拟，我们发现 MGDG 到 DGDG 的重塑以独特的方式保护叶绿体膜，同时决定了与相邻膜形成的融合柄的程度和模式。具体而言，富含 MGDG 的膜在中度脱水水平下形成长柄，而富含 DGDG 的膜则形成较小的圆形柄。对野生型和突变拟南芥（Arabidopsis thaliana）外叶绿体膜的模拟进一步证实，由于缺乏半乳糖脂重塑，突变膜中 MGDD 含量较高，更容易发生膜融合。我们的工作揭示了控制膜融合结构模式和程度的潜在物理机制，为具有提高脱水耐性的作物的理性遗传工程铺平了道路。
