Zhang Min, Chen Cheng, Froehlich John E, TerBush Allan D, Osteryoung Katherine W
Department of Plant Biology (M.Z., C.C., A.D.T., K.W.O.), Michigan State University-Department of Energy Plant Research Laboratory (J.E.F.), and Department of Biochemistry and Molecular Biology (J.E.F.), Michigan State University, East Lansing, Michigan 48824; andCollege of Life Sciences, Capital Normal University, Beijing 100048, China (M.Z.).
Department of Plant Biology (M.Z., C.C., A.D.T., K.W.O.), Michigan State University-Department of Energy Plant Research Laboratory (J.E.F.), and Department of Biochemistry and Molecular Biology (J.E.F.), Michigan State University, East Lansing, Michigan 48824; andCollege of Life Sciences, Capital Normal University, Beijing 100048, China (M.Z.)
Plant Physiol. 2016 Jan;170(1):250-62. doi: 10.1104/pp.15.01460. Epub 2015 Nov 2.
Chloroplast division is driven by the simultaneous constriction of the inner FtsZ ring (Z ring) and the outer DRP5B ring. The assembly and constriction of these rings in Arabidopsis (Arabidopsis thaliana) are coordinated partly through the inner envelope membrane protein ACCUMULATION AND REPLICATION OF CHLOROPLASTS6 (ARC6). Previously, we showed that PARC6 (PARALOG OF ARC6), also in the inner envelope membrane, negatively regulates FtsZ assembly and acts downstream of ARC6 to position the outer envelope membrane protein PLASTID DIVISION1 (PDV1), which functions together with its paralog PDV2 to recruit DYNAMIN-RELATED PROTEIN 5B (DRP5B) from a cytosolic pool to the outer envelope membrane. However, whether PARC6, like ARC6, also functions in coordination of the chloroplast division contractile complexes was unknown. Here, we report a detailed topological analysis of Arabidopsis PARC6, which shows that PARC6 has a single transmembrane domain and a topology resembling that of ARC6. The newly identified stromal region of PARC6 interacts not only with ARC3, a direct inhibitor of Z-ring assembly, but also with the Z-ring protein FtsZ2. Overexpression of PARC6 inhibits FtsZ assembly in Arabidopsis but not in a heterologous yeast system (Schizosaccharomyces pombe), suggesting that the negative regulation of FtsZ assembly by PARC6 is a consequence of its interaction with ARC3. A conserved carboxyl-terminal peptide in FtsZ2 mediates FtsZ2 interaction with both PARC6 and ARC6. Consistent with its role in the positioning of PDV1, the intermembrane space regions of PARC6 and PDV1 interact. These findings provide new insights into the functions of PARC6 and suggest that PARC6 coordinates the inner Z ring and outer DRP5B ring through interaction with FtsZ2 and PDV1 during chloroplast division.
叶绿体分裂由内部的FtsZ环（Z环）和外部的DRP5B环同时收缩驱动。这些环在拟南芥（Arabidopsis thaliana）中的组装和收缩部分通过内膜蛋白叶绿体积累与复制蛋白6（ARC6）进行协调。此前，我们发现同样位于内膜的PARC6（ARC6的旁系同源物）对FtsZ组装起负调控作用，并在ARC6下游发挥作用，定位外膜蛋白质体分裂蛋白1（PDV1），PDV1与其旁系同源物PDV2共同作用，从细胞质库中招募动力相关蛋白5B（DRP5B）至外膜。然而，PARC6是否像ARC6一样，也在叶绿体分裂收缩复合体的协调中发挥作用尚不清楚。在此，我们报道了对拟南芥PARC6的详细拓扑分析，结果表明PARC6具有单个跨膜结构域，其拓扑结构与ARC6相似。新鉴定的PARC6的基质区域不仅与Z环组装的直接抑制剂ARC3相互作用，还与Z环蛋白FtsZ2相互作用。PARC6的过表达抑制拟南芥中FtsZ的组装，但在异源酵母系统（裂殖酵母）中则不然，这表明PARC6对FtsZ组装的负调控是其与ARC3相互作用的结果。FtsZ2中一个保守的羧基末端肽介导FtsZ2与PARC6和ARC6的相互作用。与其在PDV1定位中的作用一致，PARC6和PDV1的膜间隙区域相互作用。这些发现为PARC6的功能提供了新的见解，并表明PARC6在叶绿体分裂过程中通过与FtsZ2和PDV1相互作用来协调内部的Z环和外部的DRP5B环。
