Copenhagen Plant Science Centre, Department of Plant and Environmental Sciences, University of Copenhagen, 1871 Copenhagen, Denmark.
Max Planck Institute of Molecular Plant Physiology, Department of Organelle Biology, Biotechnology and Molecular Ecophysiology, 14476 Potsdam, Germany.
Proc Natl Acad Sci U S A. 2021 Oct 19;118(42). doi: 10.1073/pnas.2113934118.
The term "de-etiolation" refers to the light-dependent differentiation of etioplasts to chloroplasts in angiosperms. The underlying process involves reorganization of prolamellar bodies (PLBs) and prothylakoids into thylakoids, with concurrent changes in protein, lipid, and pigment composition, which together lead to the assembly of active photosynthetic complexes. Despite the highly conserved structure of PLBs among land plants, the processes that mediate PLB maintenance and their disassembly during de-etiolation are poorly understood. Among chloroplast thylakoid membrane-localized proteins, to date, only Curvature thylakoid 1 (CURT1) proteins were shown to exhibit intrinsic membrane-bending capacity. Here, we show that CURT1 proteins, which play a critical role in grana margin architecture and thylakoid plasticity, also participate in de-etiolation and modulate PLB geometry and density. Lack of CURT1 proteins severely perturbs PLB organization and vesicle fusion, leading to reduced accumulation of the light-dependent enzyme protochlorophyllide oxidoreductase (LPOR) and a delay in the onset of photosynthesis. In contrast, overexpression of CURT1A induces excessive bending of PLB membranes, which upon illumination show retarded disassembly and concomitant overaccumulation of LPOR, though without affecting greening or the establishment of photosynthesis. We conclude that CURT1 proteins contribute to the maintenance of the paracrystalline PLB morphology and are necessary for efficient and organized thylakoid membrane maturation during de-etiolation.
“脱黄化”是指被子植物中依赖光的质体由前质体向叶绿体的分化。这个过程涉及到原板层体（PLB）和前质体向类囊体的重组，同时伴随着蛋白质、脂质和色素组成的变化，这些变化共同导致活性光合复合物的组装。尽管 PLB 在陆地植物中的结构高度保守，但介导 PLB 维持及其在脱黄化过程中解体的过程还知之甚少。在叶绿体类囊体膜定位蛋白中，到目前为止，只有曲率类囊体 1（CURT1）蛋白被证明具有内在的膜弯曲能力。在这里，我们表明，CURT1 蛋白在粒状边缘结构和类囊体可塑性中发挥关键作用，也参与脱黄化过程，并调节 PLB 的几何形状和密度。CURT1 蛋白的缺失严重破坏了 PLB 的组织和囊泡融合，导致光依赖性酶原叶绿酸氧化还原酶（LPOR）的积累减少，光合作用的开始延迟。相比之下，CURT1A 的过表达诱导 PLB 膜的过度弯曲，在光照下显示出 PLB 组装的延迟解体和 LPOR 的伴随过度积累，尽管这不会影响变绿或光合作用的建立。我们得出结论，CURT1 蛋白有助于维持准晶体 PLB 形态，并在脱黄化过程中促进类囊体膜的成熟。
