Biochemie und Physiologie der Pflanzen, Department Biologie I-Botanik, Ludwig-Maximilians-Universität München, D-82152 Planegg-Martinsried, Germany.
Plant Physiol. 2011 Apr;155(4):1709-22. doi: 10.1104/pp.110.170233. Epub 2011 Feb 22.
The membrane-spanning protein PIC1 (for permease in chloroplasts 1) in Arabidopsis (Arabidopsis thaliana) was previously described to mediate iron transport across the inner envelope membrane of chloroplasts. The albino phenotype of pic1 knockout mutants was reminiscent of iron-deficiency symptoms and characterized by severely impaired plastid development and plant growth. In addition, plants lacking PIC1 showed a striking increase in chloroplast ferritin clusters, which function in protection from oxidative stress by sequestering highly reactive free iron in their spherical protein shell. In contrast, PIC1-overexpressing lines (PIC1ox) in this study rather resembled ferritin loss-of-function plants. PIC1ox plants suffered from oxidative stress and leaf chlorosis, most likely originating from iron overload in chloroplasts. Later during growth, plants were characterized by reduced biomass as well as severely defective flower and seed development. As a result of PIC1 protein increase in the inner envelope membrane of plastids, flower tissue showed elevated levels of iron, while the content of other transition metals (copper, zinc, manganese) remained unchanged. Seeds, however, specifically revealed iron deficiency, suggesting that PIC1 overexpression sequestered iron in flower plastids, thereby becoming unavailable for seed iron loading. In addition, expression of genes associated with metal transport and homeostasis as well as photosynthesis was deregulated in PIC1ox plants. Thus, PIC1 function in plastid iron transport is closely linked to ferritin and plastid iron homeostasis. In consequence, PIC1 is crucial for balancing plant iron metabolism in general, thereby regulating plant growth and in particular fruit development.
质体跨膜蛋白 PIC1（质体中渗透酶 1）在拟南芥（Arabidopsis thaliana）中曾被描述为介导铁穿过叶绿体内部包膜的运输。pic1 敲除突变体的白化表型让人联想到缺铁症状，其特征是严重的质体发育和植物生长受损。此外，缺乏 PIC1 的植物表现出明显增加的叶绿体铁蛋白簇，这些铁蛋白簇通过将高度反应性的游离铁隔离在其球形蛋白壳中，从而在保护免受氧化应激方面发挥作用。相比之下，在这项研究中，PIC1 过表达系（PIC1ox）更类似于铁蛋白功能丧失植物。PIC1ox 植物遭受氧化应激和叶片黄化，很可能源自叶绿体中铁的过载。在生长后期，植物的生物量减少，花朵和种子发育严重缺陷。由于质体内部包膜中 PIC1 蛋白的增加，花朵组织中铁的含量升高，而其他过渡金属（铜、锌、锰）的含量保持不变。然而，种子特别显示出缺铁，这表明 PIC1 过表达将铁隔离在花朵质体中，从而无法用于种子铁的加载。此外，PIC1ox 植物中与金属运输和稳态以及光合作用相关的基因表达失调。因此，PIC1 在质体铁运输中的功能与铁蛋白和质体铁稳态密切相关。因此，PIC1 对于平衡植物铁代谢至关重要，从而调节植物生长，特别是果实发育。
