Abstract
Chloroplast movement is essential for proper functions of chloroplasts. In most plant species tested, chloroplast movement depends on actin filaments. In Arabidopsis thaliana, we identified a new system that utilizes short actin filaments (cp-actin filaments) at the chloroplast periphery of the plasma membrane side for chloroplast photorelocation and anchoring to the plasma membrane. Upon irradiation with blue light inducing chloroplast movement, cp-actin filaments relocalized to the leading edge of chloroplasts prior to and during photorelocation. Under weak light cp-actin filaments increase on stable chloroplasts, whereas when strong blue light was given cp-actins disappears transiently before biased cp-actin filament formation. These cp-actin filament regulations are mediated by phototropin. However, how cp-actin filaments generate the motive force for chloroplast movement remained to be determined. Myosin is a motor protein for actin filaments and is one of the strong candidates for a motive force generator of cp-actin filament-mediated chloroplast movement. Here, we analyzed chloroplast photorelocation movement in Arabidopsis myosin knockout mutants.
