State Key Laboratory of Hybrid Rice, College of Life Sciences, Wuhan University, Wuhan, 430072, China.
Department of Plant and Microbial Biology, University of California, Berkeley, CA, 94720, USA.
BMC Plant Biol. 2021 Feb 20;21(1):106. doi: 10.1186/s12870-021-02888-9.
Photosystem II (PSII) is a highly conserved integral-membrane multi-subunit pigment-protein complex. The proteins, pigments, lipids, and ions in PSII need to be assembled precisely to ensure a proper PSII biogenesis. D1 is the main subunit of PSII core reaction center (RC), and is usually synthesized as a precursor D1. D1 maturation by the C-terminal processing protease CtpA is essential for PSII assembly. However, the detailed mechanism about how D1 maturation affects PSII assembly is not clearly elucidated so far. In this study, Arabidopsis thaliana CtpA mutant (atctpa: SALK_056011), which lacks the D1 mature process, was used to investigate the function of this process on PSII assembly in more details.
Without the C-terminal processing of precursor D1, PSII assembly, including PSII monomer, dimer, especially PSII supercomplexes (PSII SCs), was largely compromised as reported previously. Western blotting following the BN-2D-SDS PAGE revealed that although the assembly of PSII core proteins D2, CP43 and CP47 was affected by the loss of D1 mature process, the incorporation of CP43 was affected the most, indicated by its most reduced assembly efficiency into PSII SCs. Furthermore, the slower growth of yeast cells which were co-transformed with pD1 and CP43, when compared with the ones co-transformed with mature D1 and CP43, approved the existence of D1 C-terminal tail hindered the interaction efficiency between D1 and CP43, indicating the physiological importance of D1 mature process on the PSII assembly and the healthy growth of the organisms.
The knockout Arabidopsis atctpa mutant is a good material to study the unexpected link between D1 maturation and PSII SCs assembly. The loss of D1 maturation mainly affects the incorporation of PSII core protein CP43, an inner antenna binding protein, which functions in the association of LHCII complexes to PSII dimers during the formation of PSII SCs. Our findings here provide detailed supports of the role of D1 maturation during PSII SCs assembly in higher plants.
光系统 II（PSII）是一种高度保守的整合膜多亚基色素蛋白复合物。PSII 中的蛋白质、色素、脂质和离子需要精确组装，以确保 PSII 的正确生物发生。D1 是 PSII 核心反应中心（RC）的主要亚基，通常作为前体 D1 合成。CtpA 末端加工蛋白酶对 D1 的成熟对于 PSII 的组装是必不可少的。然而，到目前为止，关于 D1 成熟如何影响 PSII 组装的详细机制还没有得到明确的阐明。在这项研究中，拟南芥 CtpA 突变体（atctpa：SALK_056011），缺乏 D1 的成熟过程，被用来更详细地研究这个过程对 PSII 组装的功能。
没有前体 D1 的 C 端加工，PSII 的组装，包括 PSII 单体、二聚体，特别是 PSII 超复合物（PSII SCs），正如之前报道的那样，受到了很大的影响。BN-2D-SDS PAGE 后的 Western blot 显示，尽管 PSII 核心蛋白 D2、CP43 和 CP47 的组装受到 D1 成熟过程缺失的影响，但 CP43 的组装受到的影响最大，这表明它组装到 PSII SCs 的效率最低。此外，与共转化成熟 D1 和 CP43 的酵母细胞相比，共转化 pD1 和 CP43 的酵母细胞生长较慢，这证明了 D1 C 端尾部的存在阻碍了 D1 和 CP43 之间的相互作用效率，表明 D1 成熟过程对 PSII 组装和生物体的健康生长具有重要的生理意义。
拟南芥 atctpa 突变体的敲除是研究 D1 成熟与 PSII SCs 组装之间意外联系的良好材料。D1 成熟的缺失主要影响 PSII 核心蛋白 CP43 的掺入，CP43 是一种内部天线结合蛋白，在 PSII SCs 形成过程中，CP43 与 LHCII 复合物结合到 PSII 二聚体上发挥作用。我们在这里的发现为 D1 成熟在高等植物 PSII SCs 组装中的作用提供了详细的支持。
