The molecular mechanism of mitochondrial fission and fusion in higher plants.

拟南芥基因组有两个相似的动力蛋白样蛋白DRP3a和DRP3b（同源性为76.7%）。据报道，DRP3a定位于叶绿体[Kang et al. (1998) Plant Mol. Biol. 38: 437]，而DRP3b在线粒体分裂中起作用[Arimura and Tsutsumi (2002) Proc. Natl.]。学会科学。[美]。使用GFP融合蛋白，我们观察到DRP3a和DRP3b在线粒体的部分，而不是在叶绿体中。此外，用GTPase结构域缺陷的DRP3a和DRP3b转化的细胞叶绿体正常，但线粒体延长。这些结果表明DRP3b和DRP3a都参与了植物线粒体的分裂。酵母中线粒体融合和分裂的平衡影响着线粒体的网状形状。关于线粒体融合是否发生在植物中，我们知之甚少。植物线粒体通常比动物线粒体数量更多，更呈粒状。blast搜索拟南芥核和线粒体基因组序列未发现与动物和酵母线粒体融合基因有明显同源性。为了确定线粒体融合是否真的发生在植物中，我们用一种靶向线粒体的光转换荧光蛋白Kaede标记洋葱表皮细胞中的线粒体，然后将细胞内一些线粒体的荧光从绿色改变为红色。红色和绿色线粒体的频繁和短暂融合通过随后重新分裂的黄色线粒体的出现而得到证实。我们还表明，线粒体分裂偶尔会发生，而没有均匀分布的类核（线粒体中的DNA-蛋白质复合物），导致在单个细胞内含有不同数量DNA的线粒体共存。线粒体中DNA含量的异质性可以通过频繁和短暂的线粒体融合来克服。

The Arabidopsis genome has two similar dynamin-like proteins, DRP3a and DRP3b (76.7% identity). DRP3a is reported to be localized in chloroplasts [Kang et al. (1998) Plant Mol. Biol. 38 : 437], while DRP3b functions in mitochondrial division [Arimura and Tsutsumi (2002) Proc. Natl. Acad. Sci. USA 99 : 5727]. Using GFP fusion proteins, we observed both DRP3a and DRP3b in portions of mitochondria but not in chloroplasts. Furthermore, cells transformed with DRP3a and DRP3b with a defective GTPase domain had normal chloroplasts but elongated mitochondria. These results imply that both DRP3b and DRP3a are involved in the division of plant mitochondria.The balance between mitochondrial fusion and fission influences the reticular shape of mitochondria in yeasts. Little is known about whether mitochondria fusion occurs in plants. Plant mitochondria are usually more numerous and more grain-shaped than animal mitochondria. blast searches of the nuclear and mitochondrial genome sequences of Arabidopsis thaliana did not find any obvious homologue of mitochondrial fusion genes found in animals and yeasts. To determine whether mitochondrial fusion actually occurs in plants, we labeled mitochondria in onion epidermal cells with a mitochondria-targeted, photoconvertible fluorescent protein Kaede and then altered the fluorescence of some of the mitochondria within a cell from green to red. Frequent and transient fusion of red and green mitochondria was demonstrated by the appearance of yellow mitochondria that subsequently redivided. We also show that mitochondrial fission occasionally occurs without an equal distribution of the nucleoid (DNA-protein complex in mitochondria), resulting in the coexistence of mitochondria containing various amounts of DNA within a single cell. The heterogeneity of DNA contents in mitochondria may be overcome by the frequent and transient fusion of mitochondria.