Department of Biology, Amherst College, Amherst, MA, 01002, USA.
Soil and Crop Sciences Section, School of Integrative Plant Science, Cornell University, Ithaca, NY, 14853, USA.
Plant J. 2021 Jul;107(1):215-236. doi: 10.1111/tpj.15286. Epub 2021 Jun 21.
Mitochondria and chloroplasts are organelles with high iron demand that are particularly susceptible to iron-induced oxidative stress. Despite the necessity of strict iron regulation in these organelles, much remains unknown about mitochondrial and chloroplast iron transport in plants. Here, we propose that Arabidopsis ferroportin 3 (FPN3) is an iron exporter that is dual-targeted to mitochondria and chloroplasts. FPN3 is expressed in shoots, regardless of iron conditions, but its transcripts accumulate under iron deficiency in roots. fpn3 mutants cannot grow as well as the wild type under iron-deficient conditions and their shoot iron levels are lower compared with the wild type. Analyses of iron homeostasis gene expression in fpn3 mutants and inductively coupled plasma mass spectrometry (ICP-MS) measurements show that iron levels in the mitochondria and chloroplasts are increased relative to the wild type, consistent with the proposed role of FPN3 as a mitochondrial/plastid iron exporter. In iron-deficient fpn3 mutants, abnormal mitochondrial ultrastructure was observed, whereas chloroplast ultrastructure was not affected, implying that FPN3 plays a critical role in the mitochondria. Overall, our study suggests that FPN3 is essential for optimal iron homeostasis.
线粒体和叶绿体是对铁需求较高的细胞器，特别容易受到铁诱导的氧化应激的影响。尽管这些细胞器中铁的调节非常严格，但对于植物中线粒体和叶绿体的铁运输仍知之甚少。在这里，我们提出拟南芥铁转运蛋白 3（FPN3）是一种定位于线粒体和叶绿体的铁输出蛋白。FPN3 在 shoots 中表达，无论铁条件如何，但在 roots 缺铁时其转录本积累。fpn3 突变体在缺铁条件下的生长情况不如野生型好，其 shoots 铁含量也低于野生型。fpn3 突变体中铁稳态基因表达的分析和电感耦合等离子体质谱（ICP-MS）测量表明，与野生型相比，线粒体和叶绿体中的铁含量增加，这与 FPN3 作为线粒体/质体铁输出蛋白的作用一致。在缺铁的 fpn3 突变体中，观察到异常的线粒体超微结构，而叶绿体超微结构不受影响，这意味着 FPN3 在线粒体中起着关键作用。总的来说，我们的研究表明 FPN3 对于铁稳态的最佳维持是必不可少的。
