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Science 338 (6107): 655-659

Copyright © 2012 by the American Association for the Advancement of Science

Chloroplast Biogenesis Is Regulated by Direct Action of the Ubiquitin-Proteasome System

Qihua Ling,* Weihua Huang,*,{dagger} Amy Baldwin,{ddagger} Paul Jarvis§

Abstract: Development of chloroplasts and other plastids depends on the import of thousands of nucleus-encoded proteins from the cytosol. Import is initiated by TOC (translocon at the outer envelope of chloroplasts) complexes in the plastid outer membrane that incorporate multiple, client-specific receptors. Modulation of import is thought to control the plastid’s proteome, developmental fate, and functions. Using forward genetics, we identified Arabidopsis SP1, which encodes a RING-type ubiquitin E3 ligase of the chloroplast outer membrane. The SP1 protein associated with TOC complexes and mediated ubiquitination of TOC components, promoting their degradation. Mutant sp1 plants performed developmental transitions that involve plastid proteome changes inefficiently, indicating a requirement for reorganization of the TOC machinery. Thus, the ubiquitin-proteasome system acts on plastids to control their development.

Department of Biology, University of Leicester, Leicester LE1 7RH, UK.

* These authors contributed equally to this work.

{dagger} Present address: Shanghai Institute of Plant Physiology and Ecology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200032, China.

{ddagger} Present address: School of Medicine, Cardiff University, Cardiff CF14 4YS, UK.

§ To whom correspondence should be addressed. E-mail: rpj3{at}

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