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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.

Original publication

DOI

10.1105/tpc.108.058768

Type

Journal article

Journal

Plant Cell

Publication Date

05/2008

Volume

20

Pages

1303 - 1315

Keywords

Arabidopsis, Arabidopsis Proteins, Chloroplasts, Cotyledon, Homeostasis, Microscopy, Electron, Transmission, Molecular Sequence Data, Mutation, Nitric Oxide, Nitric Oxide Synthase, Phylogeny, Plants, Genetically Modified, Plastids, Ribosomes, Seedlings, Signal Transduction, Sugar Phosphates, Terpenes, Transcription, Genetic