Larkin Robert M, Stefano Giovanni, Ruckle Michael E, Stavoe Andrea K, Sinkler Christopher A, Brandizzi Federica, Malmstrom Carolyn M, Osteryoung Katherine W
Department of Plant Biology, Michigan State University, East Lansing, MI 48824; Michigan State University-Department of Energy Plant Research Laboratory, Michigan State University, East Lansing, MI 48824; Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, MI 48824
Michigan State University-Department of Energy Plant Research Laboratory, Michigan State University, East Lansing, MI 48824;
Proc Natl Acad Sci U S A. 2016 Feb 23;113(8):E1116-25. doi: 10.1073/pnas.1515741113. Epub 2016 Feb 9.
Eukaryotic cells require mechanisms to establish the proportion of cellular volume devoted to particular organelles. These mechanisms are poorly understood. From a screen for plastid-to-nucleus signaling mutants in Arabidopsis thaliana, we cloned a mutant allele of a gene that encodes a protein of unknown function that is homologous to two other Arabidopsis genes of unknown function and to FRIENDLY, which was previously shown to promote the normal distribution of mitochondria in Arabidopsis. In contrast to FRIENDLY, these three homologs of FRIENDLY are found only in photosynthetic organisms. Based on these data, we proposed that FRIENDLY expanded into a small gene family to help regulate the energy metabolism of cells that contain both mitochondria and chloroplasts. Indeed, we found that knocking out these genes caused a number of chloroplast phenotypes, including a reduction in the proportion of cellular volume devoted to chloroplasts to 50% of wild type. Thus, we refer to these genes as REDUCED CHLOROPLAST COVERAGE (REC). The size of the chloroplast compartment was reduced most in rec1 mutants. The REC1 protein accumulated in the cytosol and the nucleus. REC1 was excluded from the nucleus when plants were treated with amitrole, which inhibits cell expansion and chloroplast function. We conclude that REC1 is an extraplastidic protein that helps to establish the size of the chloroplast compartment, and that signals derived from cell expansion or chloroplasts may regulate REC1.
真核细胞需要建立特定细胞器所占细胞体积比例的机制。但这些机制目前还知之甚少。通过对拟南芥中质体到细胞核信号突变体的筛选，我们克隆了一个基因的突变等位基因，该基因编码一种功能未知的蛋白质，它与另外两个功能未知的拟南芥基因以及FRIENDLY同源，FRIENDLY先前已被证明可促进拟南芥中线粒体的正常分布。与FRIENDLY不同的是，FRIENDLY的这三个同源物仅在光合生物中发现。基于这些数据，我们推测FRIENDLY扩展成了一个小基因家族，以帮助调节同时含有线粒体和叶绿体的细胞的能量代谢。事实上，我们发现敲除这些基因会导致许多叶绿体表型，包括叶绿体所占细胞体积比例降至野生型的50%。因此，我们将这些基因称为REDUCED CHLOROPLAST COVERAGE（REC）。rec1突变体中叶绿体区室的大小减少最为明显。REC1蛋白在细胞质和细胞核中积累。当用抑制细胞扩张和叶绿体功能的杀草强处理植物时，REC1被排除在细胞核之外。我们得出结论，REC1是一种质体外蛋白，有助于确定叶绿体区室的大小，并且来自细胞扩张或叶绿体的信号可能会调节REC1。
