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DEVELOPMENT AND HORMONE ACTION

Loss of 26S Proteasome Function Leads to Increased Cell Size and Decreased Cell Number in Arabidopsis Shoot Organs^{1,[C],[W],[OA]}

Plant Physiology, Biochemistry, and Molecular Biology Program, Department of Plant and Soil Sciences, College of Agriculture, University of Kentucky, Lexington, Kentucky 40546 (J.K., S.W., Y.L., J.A.S.); Kentucky Tobacco Research and Development Center, University of Kentucky, Lexington, Kentucky 40546 (D.Z.); and Department of Microbiology, Immunology, and Molecular Genetics, College of Medicine, University of Kentucky, Lexington, Kentucky 40546 (A.J.P.)

Although the final size of plant organs is influenced by environmental cues, it is generally accepted that the primary size determinants are intrinsic factors that regulate and coordinate cell proliferation and cell expansion. Here, we show that optimal proteasome function is required to maintain final shoot organ size in Arabidopsis (Arabidopsis thaliana). Loss of function of the subunit regulatory particle AAA ATPase (RPT2a) causes a weak defect in 26S proteasome activity and leads to an enlargement of leaves, stems, flowers, fruits, seeds, and embryos. These size increases are a result of increased cell expansion that compensates for a reduction in cell number. Increased ploidy levels were found in some but not all enlarged organs, indicating that the cell size increases are not caused by a higher nuclear DNA content. Partial loss of function of the regulatory particle non-ATPase (RPN) subunits RPN10 and RPN12a causes a stronger defect in proteasome function and also results in cell enlargement and decreased cell proliferation. However, the increased cell volumes in rpn10-1 and rpn12a-1 mutants translated into the enlargement of only some, but not all, shoot organs. Collectively, these data show that during Arabidopsis shoot development, the maintenance of optimal proteasome activity levels is important for balancing cell expansion with cell proliferation rates.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Jan A. Smalle (jsmalle{at}uky.edu).

^[C] Some figures in this article are displayed in color online but in black and white in the print edition.

^[W] The online version of this article contains Web-only data.

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www.plantphysiol.org/cgi/doi/10.1104/pp.109.135970

^* Corresponding author; e-mail jsmalle{at}uky.edu.

Received January 20, 2009; accepted March 18, 2009; published March 15, 2009.

This article has been cited by other articles:

				S. Wang, J. Kurepa, and J. A. Smalle The Arabidopsis 26S Proteasome Subunit RPN1a is Required for Optimal Plant Growth and Stress Responses Plant Cell Physiol., September 1, 2009; 50(9): 1721 - 1725. [Abstract] [Full Text] [PDF]