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Characterization of factors for the formation and function of thylakoid membrane biogenesis centers in Synechocystis sp. PCC 6803

机译：synechocystis sp。中类囊体膜生物发生中心形成和功能因子的表征。 pCC 6803

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摘要

In organisms performing oxygenic photosynthesis, the thylakoid membrane harbors all pigment-protein complexes of the light-dependent photosynthetic reactions, i.e. photosystems I (PSI) and II (PSII), cytochrome b6f (Cyt b6f) as well as the ATP synthase. In the cyanobacterium Synechocystis sp. PCC 6803 (hereafter Synechocystis), thylakoids are organized in membrane sheets following the cellular periphery. Occasionally, they converge toward the plasma membrane to form so-called biogenesis centers. The PratA-defined membrane (PDM) resides in the biogenesis center and has been described as the site of early PSII assembly. The de novo assembly of PSII is a process highly ordered in space and time, which requires the stepwise attachment of several precomplexes facilitated by a number of specific assembly factors. However, the exact function and importance of biogenesis centers, in particular concerning PSII assembly, remained a matter of debate.udThe absence of CurT, which represents the cyanobacterial homolog of the grana-shaping CURVATURE THYLAKOID1 protein family from Arabidopsis thaliana, resulted in massive alterations of the thylakoid membrane ultrastructure. Accordingly, the thylakoid membrane in curT- ran in circular structures without converging to the plasma membrane, thereby offered the possibility to analyze the consequences of the lack of biogenesis centers for the first time. Hence, curT- displayed a severe increase in doubling time and a decrease in photosynthetic activity. The absence of biogenesis centers gave rise to a reduction in PSII accumulation, assembly and repair whereas PSI and Cyt b6f were not affected. In the wild-type, CurT was distributed all over the thylakoids, locally accumulating in biogenesis centers. Moreover, CurT formed high-molecular-weight complexes in PDMs and thylakoids, differing in size and isoform composition. Furthermore, a massive relocalization of CurT to the plasma membrane occured during osmotic stress and interestingly, the absence of CurT resulted in an increased sensitivity to osmotic stress in curT-. Since curT- was able to accumulate osmotic stress-related compatible solutes in wild-type-like amounts and dynamics, an independent function of CurT via membrane stabilization in osmotic stress tolerance is proposed. Thus, the establishment of thylakoid membrane architecture and the formation of biogenesis centers depend on CurT, which enhances photosynthetic performance and viability of Synechocystis.udThe protein Slr0151 has previously been assigned as a factor contributing to PSII repair. Here, evidence of an additional involvement of Slr0151 in de novo assembly of PSII is provided. In addition, a partial localization of PSII repair to biogenesis centers is discussed.udIn conclusion, the data presented in this thesis significantly enhances the current knowledge on biogenesis center formation and their PSII-specific function in Synechocystis.
机译：在进行氧气光合作用的生物中，类囊体膜包含光依赖型光合作用反应的所有色素-蛋白质复合物，即光系统I（PSI）和II（PSII），细胞色素b6f（Cyt b6f）以及ATP合酶。在蓝藻中，Synechocystis sp.。 PCC 6803（以下称集囊藻），类囊体组织在细胞周围的膜片中。有时，它们向质膜会聚，形成所谓的生物发生中心。 PratA定义的膜（PDM）位于生物发生中心，并已被描述为早期PSII组装的位点。 PSII的从头组装是一个在空间和时间上高度有序的过程，它需要逐步连接多个预配合物，这些配合物受许多特定的组装因素的促进。然而，生物发生中心的确切功能和重要性，特别是关于PSII装配的问题，仍然是一个争论的问题。 udCurT的缺乏，代表了拟南芥中造粒的CURVATURE THYLAKOID1蛋白家族的蓝细菌同源物，导致大量的类囊体膜超微结构的改变。因此，curT-中的类囊体膜呈圆形结构而未收敛至质膜，从而提供了首次分析缺乏生物发生中心的后果的可能性。因此，curT-显示出倍增时间的严重增加和光合作用活性的降低。没有生物发生中心会导致PSII积累，组装和修复的减少，而PSI和Cyt b6f则不受影响。在野生型中，CurT分布在整个类囊体中，在生物发生中心局部积累。此外，CurT在PDM和类囊体中形成高分子量的复合物，其大小和同工型组成不同。此外，在渗透胁迫期间发生了CurT大量向质膜的重新定位，有趣的是，缺少CurT导致curT-对渗透胁迫的敏感性增加。由于curT-能够以野生型的量和动力学积累渗透压相关的相容性溶质，因此提出了CurT通过膜稳定作用在渗透压耐受性中的独立功能。因此，类囊体膜结构的建立和生物发生中心的形成依赖于CurT，从而增强了光合胞藻的光合作用性能和活力。 udSlr0151蛋白以前被认为是有助于PSII修复的因子。在此，提供了Slr0151在PSII的从头组装中进一步参与的证据。此外，还讨论了PSII修复对生物发生中心的部分定位。 ud最后，本论文中提供的数据显着增强了目前对生物合成中心形成及其PSII特定功能的认识。

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    Heinz Steffen;

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