Plant and Cell Physiology Advance Access originally published online on January 19, 2008
Plant and Cell Physiology 2008 49(3):345-361; doi:10.1093/pcp/pcn012
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The Assembly of the FtsZ Ring at the Mid-Chloroplast Division Site Depends on a Balance Between the Activities of AtMinE1 and ARC11/AtMinD1
1RIKEN, Hirosawa 2-1, Wako, Saitama, 351-0198 Japan
2Department of Life Sciences, University of Tokyo, Komaba 3-8-1, Tokyo, 153-8902 Japan
3Department of Chemistry, Biology and Marine Science, Faculty of Science, University of the Ryukyus, Senbaru 1, Nishihara, Okinawa, 903-0213 Japan
*Corresponding authors: Makoto T. Fujiwara, E-mail, mtf1{at}mac.com; Fax, +81-3-5454-6998; Ryuuichi D. Itoh, E-mail, ryuitoh{at}sci.u-ryukyu.ac.jp; Fax, +81-98-895-8576
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Abstract |
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Chloroplast division comprises a sequence of events that facilitate symmetric binary fission and that involve prokaryotic-like stromal division factors such as tubulin-like GTPase FtsZ and the division site regulator MinD. In Arabidopsis, a nuclear-encoded prokaryotic MinE homolog, AtMinE1, has been characterized in terms of its effects on a dividing or terminal chloroplast state in a limited series of leaf tissues. However, the relationship between AtMinE1 expression and chloroplast phenotype remains to be fully elucidated. Here, we demonstrate that a T-DNA insertion mutation in AtMinE1 results in a severe inhibition of chloroplast division, producing motile dots and short filaments of FtsZ. In AtMinE1 sense (overexpressor) plants, dividing chloroplasts possess either single or multiple FtsZ rings located at random intervals and showing constriction depth, mainly along the chloroplast polarity axis. The AtMinE1 sense plants displayed equivalent chloroplast phenotypes to arc11, a loss-of-function mutant of AtMinD1 which forms replicating mini-chloroplasts. Furthermore, a certain population of FtsZ rings formed within developing chloroplasts failed to initiate or progress the membrane constriction of chloroplasts and consequentially to complete chloroplast fission in both AtMinE1 sense and arc11/atminD1 plants. Our present data thus demonstrate that the chloroplast division site placement involves a balance between the opposing activities of AtMinE1 and AtMinD1, which acts to prevent FtsZ ring formation anywhere outside of the mid-chloroplast. In addition, the imbalance caused by an AtMinE1 dominance causes multiple, non-synchronous division events at the single chloroplast level, as well as division arrest, which becomes apparent as the chloroplasts mature, in spite of the presence of FtsZ rings.
Keywords: Arabidopsis thaliana - Binary fission - FtsZ ring - Leaf development - Min system
Abbreviations: CaMV, cauliflower mosaic virus; Col, Columbia; GFP, green fluorescent protein; LB, left border; Ler, Landsberg erecta; PDS, potential division site; RT–PCR, reverse transcription–PCR; Ws, Wassilewskija; WT, wild type; YFP, yellow fluorescent protein.
(Received September 20, 2007; Accepted January 15, 2008)
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