title: Two kinesin-like proteins mediate actin-based chloroplast movement in Arabidopsis thaliana.
abstract: Organelle movement is essential for efficient cellular function in eukaryotes. Chloroplast photorelocation movement is important for plant survival as well as for efficient photosynthesis. Chloroplast movement generally is actin dependent and mediated by blue light receptor phototropins. In Arabidopsis thaliana, phototropins mediate chloroplast movement by regulating short actin filaments on chloroplasts (cp-actin filaments), and the chloroplast outer envelope protein CHUP1 is necessary for cp-actin filament accumulation. However, other factors involved in cp-actin filament regulation during chloroplast movement remain to be determined. Here, we report that two kinesin-like proteins, KAC1 and KAC2, are essential for chloroplasts to move and anchor to the plasma membrane. A kac1 mutant showed severely impaired chloroplast accumulation and slow avoidance movement. A kac1kac2 double mutant completely lacked chloroplast photorelocation movement and showed detachment of chloroplasts from the plasma membrane. KAC motor domains are similar to those of the kinesin-14 subfamily (such as Ncd and Kar3) but do not have detectable microtubule-binding activity. The C-terminal domain of KAC1 could interact with F-actin in vitro. Instead of regulating microtubules, KAC proteins mediate chloroplast movement via cp-actin filaments. We conclude that plants have evolved a unique mechanism to regulate actin-based organelle movement using kinesin-like proteins.
authors.affiliation: Department of Biology, Faculty of Sciences, Kyushu University, Fukuoka 812-8581, Japan.
authors.forename: Noriyuki
authors.initials: N
authors.lastname: Suetsugu
authors.forename: Noboru
authors.initials: N
authors.lastname: Yamada
authors.forename: Takatoshi
authors.initials: T
authors.lastname: Kagawa
authors.forename: Hisashi
authors.initials: H
authors.lastname: Yonekura
authors.forename: Taro Q P
authors.initials: TQ
authors.lastname: Uyeda
authors.forename: Akeo
authors.initials: A
authors.lastname: Kadota
authors.forename: Masamitsu
authors.initials: M
authors.lastname: Wada
mesh_terms: D008841:Actin Cytoskeleton / Q000378:metabolism; D000199:Actins / Q000378:metabolism*; D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism* / Q000528:radiation effects; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism / Q000528:radiation effects; D002736:Chloroplasts / Q000378:metabolism* / Q000528:radiation effects; D003001:Cloning, Molecular; D018506:Gene Expression Regulation, Plant / Q000528:radiation effects; D017343:Genes, Plant / Q000235:genetics; D007425:Intracellular Membranes / Q000378:metabolism / Q000528:radiation effects; D016547:Kinesins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008027:Light; D009068:Movement / Q000502:physiology* / Q000528:radiation effects; D009154:Mutation / Q000235:genetics; D011485:Protein Binding / Q000528:radiation effects; D012995:Solubility / Q000528:radiation effects; D013347:Subcellular Fractions / Q000378:metabolism
chemical_list: D000199:Actins; D029681:Arabidopsis Proteins; C549626:KAC1 protein, Arabidopsis; C549627:KAC2 protein, Arabidopsis; D016547:Kinesins