Research on the mechanism of chloroplast movement

细胞器运动对于所有细胞实现有效和稳定的细胞功能是必不可少的。叶绿体运动是植物细胞中细胞器运动的代表。根据环境光，叶绿体在细胞内重新定位，以最大限度地捕获光合作用的光，并避免在过量光下的光损伤。这些运动由蓝光受体，光亲素1和2（phot 1，phot 2）调节，并依赖于肌动蛋白丝。然而，运动的分子机制仍有待阐明。在这项研究中，我们表明，叶绿体利用一个独特的肌动蛋白为基础的运动机制。在拟南芥植物中的肌动蛋白在体内成像显示，位于叶绿体周边的短肌动蛋白（指定为cp-肌动蛋白）负责叶绿体的光迁移。响应蓝光，cp-肌动蛋白在运动之前重新定位在叶绿体的前缘。相比之下，cp-肌动蛋白在静止时驻留在叶绿体周围，从而将叶绿体锚定在细胞内的特定位点。突变体分析表明，趋光蛋白调节偏cp-肌动蛋白重新定位。我们的研究结果表明，在植物细胞中存在一种新的肌动蛋白为基础的运动机制，这是不同的动物和微生物中发现的。

Organelle motility is essential for all cells to accomplish efficient and stable cellular functions. Chloroplast movement is representative of organelle motility in plant cells. According to their ambient light, chloroplasts relocate within cells to maximize light capture for photosynthesis and to avoid photodamage under excess light. These movements are regulated by blue light receptors, phototropinl and 2 (phot1, phot2) and depend on actin filaments. However, the molecular mechanisms underlying movement remain to be elucidated. In this research, we showed that chloroplasts utilize a unique actin-based movement mechanism. In vivo imaging of actins in Arabidopsis plants reveals that short actins located at the chloroplast periphery (designated as cp-actin) are responsible for chloroplast photorelocation. In response to blue light, cp-actins become relocalized at the leading edge of chloroplasts prior to movement. By contrast, cp-actins reside around the chloroplast periphery when stationary, thereby anchoring the chloroplast to a particular site within the cell. Mutant analyses indicate that phototropins regulate biased cp-actin relocalization. Our findings demonstrate the presence of a novel actin-based movement machinery in plant cells that is distinct to those found in animals and microorganisms.