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Plant Cell Advance Online Publication
Published on May 9, 2008; 10.1105/tpc.108.058768

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Received February 11, 2008
Returned for revision March 18, 2008
Accepted April 22, 2008

A Mutant Impaired in the Production of Plastome-Encoded Proteins Uncovers a Mechanism for the Homeostasis of Isoprenoid Biosynthetic Enzymes in Arabidopsis Plastids

Úrsula Flores-Pérez 1, Susanna Sauret-Güeto 2, Elisabet Gas 1, Paul Jarvis 3, and Manuel Rodríguez-Concepción 1*

1 Departament de Genètica Molecular de Plantes, Centre for Research on Agricultural Genomics, 08034 Barcelona, Spain; Departament de Bioquímica i Biologia Molecular, Universitat de Barcelona, 08028 Barcelona, Spain
2 Departament de Bioquímica i Biologia Molecular, Universitat de Barcelona, 08028 Barcelona, Spain
3 Department of Biology, University of Leicester, Leicester LE1 7RH, United Kingdom

* To whom correspondence should be addressed. E-mail: mrcgmp{at}ibmb.csic.es.

The plastid-localized methylerythritol phosphate (MEP) pathway synthesizes the isoprenoid precursors for the production of essential photosynthesis-related compounds and hormones. We have identified an Arabidopsis thaliana mutant, rif1, in which posttranscriptional upregulation of MEP pathway enzyme levels is caused by the loss of function of At3g47450, a gene originally reported to encode a mitochondrial protein related to nitric oxide synthesis. However, we show that nitric oxide is not involved in the regulation of the MEP pathway and that the encoded protein is a plastid-targeted homolog of the Bacillus subtilis YqeH protein, a GTPase required for proper ribosome assembly. Consistently, in rif1 seedlings, decreased levels of plastome-encoded proteins were observed, with the exception of ClpP1, a catalytic subunit of the plastidial Clp protease complex. The unexpected accumulation of ClpP1 in plastids with reduced protein synthesis suggested a compensatory mechanism in response to decreased Clp activity levels. In agreement, a negative correlation was found between Clp protease activity and MEP pathway enzyme levels in different experiments, suggesting that Clp-mediated degradation of MEP pathway enzymes might be a mechanism used by individual plastids to finely adjust plastidial isoprenoid biosynthesis to their functional and physiological states.






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