Department of Botany, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan.
Curr Biol. 2013 Sep 23;23(18):1776-81. doi: 10.1016/j.cub.2013.07.035. Epub 2013 Aug 22.
The cell nucleus communicates with the cytoplasm through a nucleocytoplasmic linker that maintains the shape of the nucleus and mediates its migration. In contrast to animal nuclei, which are moved by motor proteins (kinesins and dyneins) along the microtubule cytoskeleton, plant nuclei move rapidly and farther along an actin filament cytoskeleton. This implies that plants use a distinct nucleocytoplasmic linker for nuclear dynamics, although its molecular identity is unknown. Here, we describe a new type of nucleocytoplasmic linker consisting of a myosin motor and nuclear membrane proteins. In the Arabidopsis thaliana mutant kaku1, nuclear movement was impaired and the nuclear envelope was abnormally invaginated. The responsible gene was identified as myosin XI-i, which encodes a plant-specific myosin. Myosin XI-i is specifically localized on the nuclear membrane, where it physically interacts with the outer-nuclear-membrane proteins WIT1 and WIT2. Both WIT proteins are required for anchoring myosin XI-i to the nuclear membrane and for nuclear movement. A striking feature of plant cells is dark-induced nuclear positioning in mesophyll cells. A deficiency of either myosin XI-i or WIT proteins diminished dark-induced nuclear positioning. The unique nucleocytoplasmic linkage in plants might enable rapid nuclear positioning in response to environmental stimuli.
细胞核通过核质连接蛋白与细胞质进行通讯，核质连接蛋白维持细胞核的形状并介导其迁移。与动物细胞核不同，动物细胞核通过沿微管细胞骨架运动的马达蛋白（驱动蛋白和动力蛋白）移动，而植物细胞核则沿肌动蛋白细胞骨架快速而远距离地移动。这意味着植物使用一种独特的核质连接蛋白来实现核动态，尽管其分子身份尚不清楚。在这里，我们描述了一种由肌球蛋白马达和核膜蛋白组成的新型核质连接蛋白。在拟南芥突变体 kaku1 中，核运动受到损害，核膜异常内陷。负责的基因被鉴定为肌球蛋白 XI-i，它编码一种植物特异性的肌球蛋白。肌球蛋白 XI-i 特异性定位于核膜上，在那里它与核膜外膜蛋白 WIT1 和 WIT2 发生物理相互作用。WIT 蛋白对于将肌球蛋白 XI-i 锚定在核膜上和核运动都是必需的。植物细胞的一个显著特征是在叶肉细胞中暗诱导的核定位。肌球蛋白 XI-i 或 WIT 蛋白的缺乏都会减弱暗诱导的核定位。植物中独特的核质连接可能使细胞核能够快速响应环境刺激进行定位。
