2012 Volume 24 Issue 1 Pages 19-22
Intracellular distribution of chloroplasts is regulated by light and the motile system of chloroplast relocation movement generally depends on actin filaments. The basic mechanism, however, has not been explored. We examined the dynamic behavior of actin filaments during chloroplast movement in transformed plants expressing GFP-mouse talin. Using custom made fluorescent time-lapse imaging system equipped with a microbeam irradiator, we found short actin filaments exhibiting rapid turnover along the chloroplast periphery, termed as chloroplast-actin filaments (cp-actin filaments). Cp-actin filaments showed biased localiztion on the leading edge of chloroplasts during chloroplast movement and the biased localization was cancelled in conjunction with chloroplast anchoring. In Arabidopsis thaliana, no apparent cp-actin filaments formation was observed in chloroplast unusual positioning 1 (chup1) mutant plants that is impaired in a gene encoding an actin-binding protein. Furthermore, cp-actin filaments and their biased localization during chloroplast movement were observed in protonema cells of Physcomitrella patens. These data suggest that plants evolved a unique actin-based motile system for chloroplast movement.
