Wietrzynski Wojciech, Lamm Lorenz, Wood William H J, Loukeri Matina-Jasemi, Malone Lorna, Peng Tingying, Johnson Matthew P, Engel Benjamin D
Biozentrum, University of Basel, Basel, Switzerland.
Helmholtz AI, Helmholtz Zentrum München, Neuherberg, Germany.
Elife. 2025 Sep 11;14:RP105496. doi: 10.7554/eLife.105496.
Thylakoid membranes coordinate the light reactions of photosynthesis across multiple scales, coupling the architecture of an elaborate membrane network to the spatial organization of individual protein complexes embedded within this network. Previously, we used in situ cryo-electron tomography (cryo-ET) to reveal the native thylakoid architecture of the green alga (Engel et al., 2015) and then map the molecular organization of these thylakoids with single-molecule precision (Wietrzynski et al., 2020). However, it remains to be shown how generalizable this green algal blueprint is to the thylakoids of vascular plants, which possess distinct membrane architecture subdivided into grana stacks interconnected by non-stacked stromal lamellae. Here, we continue our cryo-ET investigation to reveal the molecular architecture of thylakoids within intact chloroplasts isolated from spinach (). We visualize the fine ultrastructural details of grana membranes, as well as interactions between thylakoids and plastoglobules. We apply AI-based computational approaches (Lamm et al., 2024) to quantify the organization of photosynthetic complexes within the plane of the thylakoid membrane and across adjacent stacked membranes. Our analysis reveals that the molecular organization of thylakoid membranes in vascular plants and green algae is strikingly similar. We find that PSII organization is non-crystalline and has uniform concentration both within the membrane plane and across stacked grana membranes. Similar to , we observe strict lateral heterogeneity of PSII and PSI at the boundary between appressed and non-appressed thylakoid domains, with no evidence for a distinct grana margin region where these complexes have been proposed to intermix. Based on these measurements, we support a simple two-domain model for the molecular organization of thylakoid membranes in both green algae and plants.
类囊体膜在多个尺度上协调光合作用的光反应，将复杂膜网络的结构与嵌入该网络的单个蛋白质复合物的空间组织联系起来。此前，我们利用原位冷冻电子断层扫描（cryo-ET）揭示了绿藻的天然类囊体结构（恩格尔等人，2015年），然后以单分子精度绘制了这些类囊体的分子组织图（维特日恩斯基等人，2020年）。然而，这种绿藻蓝图对维管植物类囊体的普遍适用性仍有待证明，维管植物具有独特的膜结构，分为由非堆叠的基质类囊体连接的基粒堆叠。在这里，我们继续进行冷冻电子断层扫描研究，以揭示从菠菜中分离出的完整叶绿体中类囊体的分子结构。我们可视化了基粒膜的精细超微结构细节，以及类囊体与质体小球之间的相互作用。我们应用基于人工智能的计算方法（拉姆等人，2024年）来量化类囊体膜平面内和相邻堆叠膜上光合复合物的组织。我们的分析表明，维管植物和绿藻类囊体膜的分子组织惊人地相似。我们发现光系统II的组织是非晶体状的，在膜平面内和堆叠的基粒膜上浓度均匀。与……类似，我们在紧密和非紧密类囊体结构域之间的边界处观察到光系统II和光系统I严格的横向异质性，没有证据表明存在一个不同的基粒边缘区域，有人提出这些复合物会在该区域混合。基于这些测量结果，我们支持一个简单的两结构域模型，用于解释绿藻和植物中类囊体膜的分子组织。
