CURT1-mediated thylakoid plasticity is required for fine-tuning photosynthesis and plant fitness

The thylakoid (类囊体) membrane system of higher-plant chloroplasts consists of interconnected subdomains (互相连接的亚结构域) of appressed (紧靠的) and non-appressed membrane bilayers (双层膜), known as grana and stroma lamellae (基粒和基质片层), respectively. The shaping of the cylindrical grana stacks (圆柱形基粒垛) is mediated, in a dosage-dependent manner, by CURT1 protein complexes, which facilitate membrane curvature (膜曲率) at the grana margins, the interface between grana and stroma lamellae. Although grana stacks are highly conserved among land plants, the functional relevance (功能关联) of grana stacking remains unclear. Here we show that CURT1-related alteration of thylakoid ultrastructure (超微结构) reduces photosynthetic efficiency and plant fitness under adverse (不利的), controlled and natural light conditions. Plants that lack CURT1 are impaired (有缺陷的) in adjusting grana diameter (基粒直径), which compromises the effectiveness of regulatory mechanisms like PSII repair cycle and state transitions. Interestingly, CURT1A suffices (足够) to induce thylakoid membrane curvature in planta, and thylakoid hyper-bending (超弯曲) that is observed in CURT1A overexpressor lines. We suggest that CURT1 oligomerisation (寡聚) is regulated at the post-translational level (翻译后水平) in a light-dependent fashion and CURT1-mediated thylakoid plasticity (类囊体可塑性) is critical for plant fitness and plays an important role in fine-tuning photosynthesis under challenging growth conditions.

高等植物叶绿体的类囊体膜系统由紧靠着和不紧靠着的双层膜，即基粒和基质片层的互相连接的亚结构域构成。圆柱形基粒垛的塑造是由CURT1蛋白复合物通过剂量效应的方式调控的，CURT1蛋白复合物会促进基粒边缘膜卷曲，也就是基粒和基质片层的交界处。尽管基粒垛在高等植物中高度保守，然而基粒垛的功能方面的研究还不是很多。本文揭示了类囊体超微结构CURT1相关的改变会减少植物在不利的、控制的和自然的光照条件下的光合效率和植物适应性。缺少CURT1的植物在调整基粒直径方面存在缺陷，而基粒直径是保证PSII修复周期和状态改变等调控机制有效性的基础。有趣的是，CURT1A能够诱导植物中的类囊体膜卷曲，在CURT1A过表达株系中观察到类囊体的超弯曲。作者认为CURT1寡聚受光依赖性的翻译后水平调控，CURT1介导的类囊体可塑性对于植物适应性至关重要，并在植物胁迫生长条件下的光合作用精细调控中起重要作用。

通讯：Dario Leister (http://www.en.botanik.bio.lmu.de/research/leister/index.html)

研究方向：光合作用的调控；STN7和GUN1相关的质体信号转导。

doi: https://doi.org/10.1104/pp.17.00863