Chotewutmontri Prakitchai, Williams-Carrier Rosalind, Barkan Alice
Institute of Molecular Biology, University of Oregon, Eugene, OR 97403, USA.
Plants (Basel). 2020 Jan 25;9(2):152. doi: 10.3390/plants9020152.
Photosystem II (PSII) in chloroplasts and cyanobacteria contains approximately fifteen core proteins, which organize numerous pigments and prosthetic groups that mediate the light-driven water-splitting activity that drives oxygenic photosynthesis. The PSII reaction center protein D1 is subject to photodamage, whose repair requires degradation of damaged D1 and its replacement with nascent D1. Mechanisms that couple D1 synthesis with PSII assembly and repair are poorly understood. We address this question by using ribosome profiling to analyze the translation of chloroplast mRNAs in maize and Arabidopsis mutants with defects in PSII assembly. We found that OHP1, OHP2, and HCF244, which comprise a recently elucidated complex involved in PSII assembly and repair, are each required for the recruitment of ribosomes to mRNA, which encodes D1. By contrast, HCF136, which acts upstream of the OHP1/OHP2/HCF244 complex during PSII assembly, does not have this effect. The fact that the OHP1/OHP2/HCF244 complex brings D1 into proximity with three proteins with dual roles in PSII assembly and ribosome recruitment suggests that this complex is the hub of a translational autoregulatory mechanism that coordinates D1 synthesis with need for nascent D1 during PSII biogenesis and repair.
叶绿体和蓝细菌中的光系统II（PSII）包含大约15种核心蛋白，这些蛋白组织了众多色素和辅基，介导驱动光合放氧的光驱动水裂解活性。PSII反应中心蛋白D1易受光损伤，其修复需要降解受损的D1并用新生的D1进行替换。将D1合成与PSII组装和修复相偶联的机制尚不清楚。我们通过核糖体分析来分析玉米和拟南芥PSII组装缺陷突变体中叶绿体mRNA的翻译，从而解决这个问题。我们发现，OHP1、OHP2和HCF244（它们构成了一个最近阐明的参与PSII组装和修复的复合体）各自都是核糖体募集到编码D1的mRNA所必需的。相比之下，在PSII组装过程中作用于OHP1/OHP2/HCF244复合体上游的HCF136则没有这种作用。OHP1/OHP2/HCF244复合体使D1与在PSII组装和核糖体募集中具有双重作用的三种蛋白靠近，这一事实表明，该复合体是一种翻译自调控机制的枢纽，在PSII生物发生和修复过程中协调D1合成与对新生D1的需求。
