Molekularbiologie der Pflanzen (Botanik), Department Biologie I, Ludwig-Maximilians-Universität München, Martinsried, 82152, Germany.
Department of Plant and Environmental Sciences and Copenhagen Plant Science Centre (CPSC), Faculty of Science, University of Copenhagen, Frederiksberg C, 1871, Denmark.
New Phytol. 2017 Jul;215(1):256-268. doi: 10.1111/nph.14526. Epub 2017 Mar 20.
Manganese (Mn) is an essential constituent of photosystem II (PSII) and therefore indispensable for oxygenic photosynthesis. Very little is known about how Mn is transported, delivered and retained in photosynthetic cells. Recently, the thylakoid-localized transporter PAM71 has been linked to chloroplast Mn homeostasis in Arabidopsis thaliana. Here, we characterize the function of its homolog in Synechocystis (SynPAM71). We used a loss-of-function line (ΔSynPAM71), wild-type (WT) cells exposed to Mn stress and strains expressing a tagged variant of SynPAM71 to characterize the role of SynPAM71 in cyanobacterial Mn homeostasis. The ΔSynPAM71 strain displays an Mn-sensitive phenotype with reduced levels of chlorophyll and PSI accumulation, defects in PSII photochemistry and intracellular Mn enrichment, particularly in the thylakoid membranes. These effects are attributable to Mn toxicity, as very similar symptoms were observed in WT cells exposed to excess Mn. Moreover, CyanoP, which is involved in the early steps of PSII assembly, is massively upregulated in ΔSynPAM71. SynPAM71 was detected in both the plasma membrane and, to a lesser extent, the thylakoid membranes. Our results suggest that SynPAM71 is involved in the maintenance of Mn homeostasis through the export of Mn from the cytoplasm into the periplasmic and luminal compartments, where it can be stored without interfering with cytoplasmic metabolic processes.
锰（Mn）是光系统 II（PSII）的必需组成部分，因此对产氧光合作用是不可或缺的。关于 Mn 如何在光合细胞中运输、传递和保留，人们知之甚少。最近，定位于类囊体的转运蛋白 PAM71 与拟南芥叶绿体 Mn 稳态有关。在这里，我们对其在集胞藻（SynPAM71）中的同源物的功能进行了表征。我们使用了一个功能丧失系（ΔSynPAM71）、野生型（WT）细胞暴露于 Mn 胁迫和表达 SynPAM71 标记变体的菌株，以表征 SynPAM71 在蓝藻 Mn 稳态中的作用。ΔSynPAM71 菌株表现出 Mn 敏感表型，叶绿素和 PSI 积累减少，PSII 光化学和细胞内 Mn 富集缺陷，特别是在类囊体膜中。这些效应归因于 Mn 毒性，因为在暴露于过量 Mn 的 WT 细胞中观察到非常相似的症状。此外，CyanoP，它参与 PSII 组装的早期步骤，在 ΔSynPAM71 中大量上调。SynPAM71 被检测到存在于质膜中，并且在较小程度上存在于类囊体膜中。我们的结果表明，SynPAM71 通过将 Mn 从细胞质输出到周质和腔室中，参与维持 Mn 稳态，在那里 Mn 可以储存而不会干扰细胞质代谢过程。
