Graduate School of Science, Rikkyo University, 3-34-1 Nishiikebukuro, Toshima-ku, Tokyo 171-8501, Japan.
J Cell Sci. 2013 Jun 1;126(Pt 11):2392-400. doi: 10.1242/jcs.116798. Epub 2013 Apr 2.
The cell cycle usually refers to the mitotic cycle, but the cell-division cycle in the plant kingdom consists of not only nuclear but also mitochondrial and chloroplast division cycle. However, an integrated control system that initiates division of the three organelles has not been found. We report that a novel C-terminal kinesin-like protein, three-organelle division-inducing protein (TOP), controls nuclear, mitochondrial and chloroplast divisions in the red alga Cyanidioschyzon merolae. A proteomics study revealed that TOP is a member of a complex of mitochondrial-dividing (MD) and plastid-dividing (PD) machineries (MD/PD machinery complex) just prior to constriction. After TOP localizes at the MD/PD machinery complex, mitochondrial and chloroplast divisions occur and the components of the MD/PD machinery complexes are phosphorylated. Furthermore, we found that TOP downregulation impaired both mitochondrial and chloroplast divisions. MD/PD machinery complexes were formed normally at each division site but they were neither phosphorylated nor constricted in these cells. Immunofluorescence signals of Aurora kinase (AUR) were localized around the MD machinery before constriction, whereas AUR was dispersed in the cytosol by TOP downregulation, suggesting that AUR is required for the constriction. Taken together our results suggest that TOP induces phosphorylation of MD/PD machinery components to accomplish mitochondrial and chloroplast divisions prior to nuclear division, by relocalization of AUR. In addition, given the presence of TOP homologs throughout the eukaryotes, and the involvement of TOP in mitochondrial and chloroplast division may illuminate the original function of C-terminal kinesin-like proteins.
细胞周期通常是指有丝分裂周期，但植物王国的细胞分裂周期不仅包括核分裂，还包括线粒体和叶绿体分裂周期。然而，尚未发现启动这三个细胞器分裂的综合控制系统。我们报告称，一种新型的 C 端驱动蛋白样蛋白，即三细胞器分裂诱导蛋白（TOP），可控制红藻 Cyanidioschyzon merolae 的核、线粒体和叶绿体分裂。蛋白质组学研究表明，TOP 是线粒体分裂（MD）和质体分裂（PD）机器（MD/PD 机器复合物）在收缩之前的复合物的成员。TOP 定位到 MD/PD 机器复合物后，线粒体和叶绿体分裂发生，MD/PD 机器复合物的成分发生磷酸化。此外，我们发现 TOP 的下调会损害线粒体和叶绿体的分裂。MD/PD 机器复合物在每个分裂部位正常形成，但在这些细胞中既没有磷酸化也没有收缩。在收缩之前，极光激酶（AUR）的免疫荧光信号定位于 MD 机器周围，而 TOP 的下调使 AUR 在细胞质中弥散，这表明 AUR 是收缩所必需的。总的来说，我们的结果表明，TOP 通过 AUR 的重定位，诱导 MD/PD 机器成分的磷酸化，从而在核分裂之前完成线粒体和叶绿体的分裂。此外，鉴于整个真核生物中都存在 TOP 同源物，并且 TOP 参与线粒体和叶绿体分裂，这可能阐明 C 端驱动蛋白样蛋白的原始功能。
