Ogawa Yu, Iwano Megumi, Shikanai Toshiharu, Sakamoto Wataru
Institute of Plant Science and Resources, Okayama University, Kurashiki, Japan.
Graduate School of Biostudies, Kyoto University, Kyoto, Japan.
Front Plant Sci. 2023 Sep 28;14:1279699. doi: 10.3389/fpls.2023.1279699. eCollection 2023.
Photosynthetic electron transfer and its regulation processes take place on thylakoid membranes, and the thylakoid of vascular plants exhibits particularly intricate structure consisting of stacked grana and flat stroma lamellae. It is known that several membrane remodeling proteins contribute to maintain the thylakoid structure, and one putative example is FUZZY ONION LIKE (FZL). In this study, we re-evaluated the controversial function of FZL in thylakoid membrane remodeling and in photosynthesis. We investigated the sub-membrane localization of FZL and found that it is enriched on curved grana edges of thylakoid membranes, consistent with the previously proposed model that FZL mediates fusion of grana and stroma lamellae at the interfaces. The mature thylakoid morphology characterized with the staggered and less connected grana seems to agree with this model as well. In the photosynthetic analysis, the knockout mutants in displayed reduced electron flow, likely resulting in higher oxidative levels of Photosystem I (PSI) and smaller proton motive force (pmf). However, nonphotochemical quenching (NPQ) of chlorophyll fluorescence was excessively enhanced considering the pmf levels in , and we found that introducing mutation, lowering pH in thylakoid lumen, synergistically reinforced the photosynthetic disorder in the mutant background. We also showed that state transitions normally occurred in , and that they were not involved in the photosynthetic disorders in . We discuss the possible mechanisms by which the altered thylakoid morphology in leads to the photosynthetic modifications.
光合电子传递及其调控过程发生在类囊体膜上，维管植物的类囊体呈现出由堆叠的基粒和平坦的基质片层组成的特别复杂的结构。已知几种膜重塑蛋白有助于维持类囊体结构，一个可能的例子是类模糊洋葱蛋白（FZL）。在本研究中，我们重新评估了FZL在类囊体膜重塑和光合作用中存在争议的功能。我们研究了FZL在膜下的定位，发现它富集在类囊体膜弯曲的基粒边缘，这与之前提出的FZL在界面处介导基粒和基质片层融合的模型一致。以交错且连接较少的基粒为特征的成熟类囊体形态似乎也与该模型相符。在光合分析中，FZL基因敲除突变体显示电子流减少，可能导致光系统I（PSI）的氧化水平升高和质子动力势（pmf）降低。然而，考虑到FZL基因敲除突变体中的pmf水平，叶绿素荧光的非光化学猝灭（NPQ）过度增强，并且我们发现引入降低类囊体腔pH值的突变会在FZL基因敲除突变体背景下协同加剧光合紊乱。我们还表明，状态转换在FZL基因敲除突变体中正常发生，并且它们不参与FZL基因敲除突变体中的光合紊乱。我们讨论了FZL基因敲除突变体中类囊体形态改变导致光合修饰的可能机制。
