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First published online August 19, 2005; 10.1104/pp.105.067371 Plant Physiology 139:151-162 (2005) © 2005 American Society of Plant Biologists An Auxilin-Like J-Domain Protein, JAC1, Regulates Phototropin-Mediated Chloroplast Movement in Arabidopsis1,[w]Division of Photobiology, National Institute for Basic Biology, Okazaki 444–8585, Japan (N.S., T.K., M.W.); Department of Biological Sciences, Graduate School of Science, Tokyo Metropolitan University, Tokyo 192–0397, Japan (N.S., M.W.); and Solution Oriented Research for Science and Technology, Japan Science and Technology Corporation, Kawaguchi-city, Saitama 332–0012, Japan (T.K.)
The ambient-light conditions mediate chloroplast relocation in plant cells. Under the low-light conditions, chloroplasts accumulate in the light (accumulation response), while under the high-light conditions, they avoid the light (avoidance response). In Arabidopsis (Arabidopsis thaliana), the accumulation response is mediated by two blue-light receptors, termed phototropins (phot1 and phot2) that act redundantly, and the avoidance response is mediated by phot2 alone. A mutant, J-domain protein required for chloroplast accumulation response 1 (jac1), lacks the accumulation response under weak blue light but shows a normal avoidance response under strong blue light. In dark-adapted wild-type cells, chloroplasts accumulate on the bottom of cells. Both the jac1 and phot2 mutants are defective in this chloroplast movement in darkness. Positional cloning of JAC1 reveals that this gene encodes a J-domain protein, resembling clathrin-uncoating factor auxilin at its C terminus. The amounts of JAC1 transcripts and JAC1 proteins are not regulated by light and by phototropins. A green fluorescent protein-JAC1 fusion protein showed a similar localization pattern to green fluorescent protein alone in a transient expression assay using Arabidopsis mesophyll cells and onion (Allium cepa) epidermal cells, suggesting that the JAC1 protein may be a soluble cytosolic protein. Together, these results suggest that JAC1 is an essential component of phototropin-mediated chloroplast movement.
1 This work was supported by the Japan Society for the Promotion of Science for Young Scientists (research fellowship grant to N.S.); by the Solution Oriented Research for Science and Technology, Japan Science and Technology Corporation (grant to T.K.); and by the Education, Sports, Science and Technology of Japan (grants for Scientific Research on Priority Areas, no. 13139203; on A, no. 13304061; and on S, no. 16107002 to M.W.). 2 Present address: Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Ibaraki 305–8572, Japan. [w] The online version of this article contains Web-only data. Article, publication date, and citation information can be found at www.plantphysiol.org/cgi/doi/10.1104/pp.105.067371. * Corresponding author; e-mail wada{at}nibb.ac.jp; fax 81–564–55–7611. Received June 20, 2005; returned for revision July 11, 2005; accepted July 14, 2005. This article has been cited by other articles:
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