Chloroplast Actin Filaments Involved in Chloroplast Photorelocation Movements

Abstract

Plants have evolved sophisticated mechanisms to survive in various environmental changes. Chloroplast movement is an essential response to optimize photosynthesis and to avoid photodamage under fluctuating light conditions. Chloroplasts accumulate at periclinal walls to maximize light absorption under weak light while they move to anticlinal walls to minimize light exposure under strong light. The light strength is monitored by blue light receptor phototropins in general. In Arabidopsis thaliana, both phototropin1 (phot1) and phototropin2 (phot2) are involved in accumulation response, but phot2 is specifically involved in avoidance response. Such appropriate photorelocation movements of chloroplasts are mediated by a structure made of short actin filaments specialized for chloroplast movement. The short actin filaments are dynamically reorganized on the leading edges of moving chloroplasts, so that named chloroplast actin (cp-actin) filaments. In this chapter, we summarize recent knowledge about cp-actin filaments and next challenges to elucidate the underlying mechanisms.