Research on the mechanism of chloroplast movement

细胞器的运动是所有细胞完成高效和稳定的细胞功能所必需的。在植物细胞中，叶绿体运动是细胞器运动的代表。根据周围的光线，叶绿体在细胞内重新定位，以最大限度地捕捉光合作用的光，并避免在过量光下的光损害。这些运动由蓝光受体、趋光素1和2(Pho1、Pho2)调节，并依赖于肌动蛋白细丝。然而，潜在的运动的分子机制仍有待阐明。在这项研究中，我们证明了叶绿体利用一种独特的基于肌动蛋白的运动机制。对拟南芥植物中肌动蛋白的体内成像显示，位于叶绿体外围的短肌动蛋白(称为cp-肌动蛋白)负责叶绿体的光定位。作为对蓝光的响应，cp-肌动蛋白在运动之前被重新定位在叶绿体的前缘。相比之下，cp-肌动蛋白在静止时存在于叶绿体外围，从而将叶绿体锚定在细胞内的特定位置。突变分析表明，趋光性激素调节有偏向的cp-肌动蛋白重新定位。我们的发现表明，在植物细胞中存在一种新的基于肌动蛋白的运动机制，这与在动物和微生物中发现的不同。

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.