Plant Cell Journal of Pharmacology and Experimental Therapeutics
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The Plant Cell 19:2970

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IN BRIEF

MIDGET and the Function of Topoisomerase VI in Arabidopsis

Nancy A. Eckardt

News and Reviews Editor

neckardt{at}aspb.org

DNA topoisomerase VI (topo VI) is found only in archaeabacteria and plants, and in plants, it is required for the progression of endoreduplication cycles. Archaea topo VI is a heterotetramer containing two A subunits required for DNA cleavage and two B subunits that perform ATP hydrolysis. Functional topo VI A and B subunits were previously identified in Arabidopsis as TOP6B and RHL2/SPO11-3, respectively. Kirik et al. (pages 3100–3110) show that MIDGET (MID) encodes a novel plant-specific component of topo VI in Arabidopsis. mid mutants show a range of phenotypic abnormalities associated with effects on endoreduplication, such as a reduction in cell size (and plant size) and abnormal differentiation of root hairs and seed columella cells. Yeast two-hybrid assays, protein coimmunoprecipitation, and analyses of mid top6b and mid rhl2 double mutants demonstrate that MID is a component of the topo VI complex. Analysis of mid mutant plants reveals that topo VI is involved in chromatin organization and transcriptional silencing. Genetic evidence for the misregulated cell cycle suggests that a G2-specific checkpoint is activated in mid plants, which prevents progression of endoreduplication cycles.


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  		MID is required for seed epidermal differentiation. mid seed (bottom panels) do not develop the distinctive columella of wild-type seed (top panels) and fail to release seed coat mucilage after hydration.

 
Footnotes

www.plantcell.org/cgi/doi/10.1105/tpc.107.191011


Related articles in Plant Cell:

MIDGET Unravels Functions of the Arabidopsis Topoisomerase VI Complex in DNA Endoreduplication, Chromatin Condensation, and Transcriptional Silencing
Viktor Kirik, Andrea Schrader, Joachim F. Uhrig, and Martin Hulskamp
Plant Cell 2007 19: 3100-3110. [Abstract] [Full Text]  




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