Department of Biological Sciences, Graduate School of Science and Engineering, Tokyo Metropolitan University, Tokyo 192-0397, Japan.
Planta. 2011 Feb;233(2):357-68. doi: 10.1007/s00425-010-1299-2. Epub 2010 Oct 30.
Cytoskeleton dynamics during phototropin-dependent chloroplast photorelocation movement was analyzed in protonemal cells of actin- and microtubule-visualized lines of Physcomitrella patens expressing GFP- or tdTomato-talin and GFP-tubulin. Using newly developed epi- and trans-microbeam irradiation systems that permit fluorescence observation of the cell under blue microbeam irradiation inducing chloroplast relocation, it was revealed that meshwork of actin filaments formed at the chloroplast-accumulating area both in the avoidance and accumulation movements. The structure disappeared soon when blue microbeam was turned off, and it was not induced under red microbeam irradiation that did not evoke chloroplast relocation movement. In contrast, no apparent change in microtubule organization was detected during the movements. The actin meshwork was composed of short actin filaments distinct from the cytoplasmic long actin cables and was present between the chloroplasts and plasma membrane. The short actin filaments emerged from around the chloroplast periphery towards the center of chloroplast. Showing highly dynamic behavior, the chloroplast actin filaments (cp-actin filaments) were rapidly organized into meshwork on the chloroplast surface facing plasma membrane. The actin filament configuration on a chloroplast led to the formation of actin meshwork area in the cell as the chloroplasts arrived at and occupied the area. After establishment of the meshwork, cp-actin filaments were still highly dynamic, showing appearance, disappearance, severing and bundling of filaments. These results indicate that the cp-actin filaments have significant roles in the chloroplast movement and positioning in the cell.
在表达 GFP-或 tdTomato-talin 和 GFP-tubulin 的 Physcomitrella patens 的原丝体细胞中分析了光受体依赖性叶绿体光定位运动期间细胞骨架的动态变化。使用新开发的 epi-和 trans-microbeam 辐照系统，可以在蓝光微束辐照下观察到细胞，从而诱导叶绿体重新定位，揭示了在回避和积累运动中，叶绿体积累区形成的网格状肌动蛋白丝。当关闭蓝色微束时，该结构很快消失，并且在不引起叶绿体重定位运动的红色微束照射下不会诱导该结构。相比之下，在运动过程中未检测到微管组织的明显变化。肌动蛋白网格由不同于细胞质中长肌动蛋白电缆的短肌动蛋白丝组成，存在于叶绿体和质膜之间。短肌动蛋白丝从叶绿体周围向叶绿体中心出现。表现出高度动态行为的叶绿体肌动蛋白丝（cp-actin 丝）在面向质膜的叶绿体表面上迅速组织成网格。叶绿体上的肌动蛋白丝构型导致细胞中形成肌动蛋白网格区域，当叶绿体到达并占据该区域时。网格形成后，cp-actin 丝仍然高度动态，表现出纤维的出现、消失、切断和束集。这些结果表明，cp-actin 丝在叶绿体的运动和在细胞中的定位中具有重要作用。
