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ENVIRONMENTAL STRESS AND ADAPTATION TO STRESS

Degradation of Oxidized Proteins by Autophagy during Oxidative Stress in Arabidopsis^1,[W],[OA]

Department of Genetics, Development and Cell Biology (Y.X., A.L.C., P.Q.N., D.C.B.), Interdepartmental Plant Physiology Program (Y.X., D.C.B.), Plant Sciences Institute (D.C.B.), and Interdepartmental Genetics Program (P.Q.N., D.C.B.), Iowa State University, Ames, Iowa 50011

Upon encountering oxidative stress, proteins are oxidized extensively by highly reactive and toxic reactive oxidative species, and these damaged, oxidized proteins need to be degraded rapidly and effectively. There are two major proteolytic systems for bulk degradation in eukaryotes, the proteasome and vacuolar autophagy. In mammalian cells, the 20S proteasome and a specific type of vacuolar autophagy, chaperone-mediated autophagy, are involved in the degradation of oxidized proteins in mild oxidative stress. However, little is known about how cells remove oxidized proteins when under severe oxidative stress. Using two macroautophagy markers, monodansylcadaverine and green fluorescent protein-AtATG8e, we here show that application of hydrogen peroxide or the reactive oxidative species inducer methyl viologen can induce macroautophagy in Arabidopsis (Arabidopsis thaliana) plants. Macroautophagy-defective RNAi-AtATG18a transgenic plants are more sensitive to methyl viologen treatment than wild-type plants and accumulate a higher level of oxidized proteins due to a lower degradation rate. In the presence of a vacuolar H⁺-ATPase inhibitor, concanamycin A, oxidized proteins were detected in the vacuole of wild-type root cells but not RNAi-AtATG18a root cells. Together, our results indicate that autophagy is involved in degrading oxidized proteins under oxidative stress conditions in Arabidopsis.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the Journal policy described in the Instructions for Authors (http://www.plantphysiol.org) is: Diane C. Bassham (bassham{at}iastate.edu).

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

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www.plantphysiol.org/cgi/doi/10.1104/pp.106.092106

^* Corresponding author; e-mail bassham{at}iastate.edu; fax 515–294–1337.

Received October 26, 2006; accepted November 3, 2006; published November 10, 2006.

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