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

Departament de Genètica Molecular de Plantes, Centre for Research on Agricultural Genomics, 08034 Barcelona, Spain.
The Plant Cell (Impact Factor: 9.34). 06/2008; 20(5):1303-15. DOI: 10.1105/tpc.108.058768
Source: PubMed


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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Available from: Manuel Rodríguez-Concepción, Jan 13, 2015
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    • "As this apparent protection of DXR from degradation could be confirmed in isolated chloroplasts (Fig. 8B), we hypothesize that the substrate-like tight binding of fosmidomycin to the active site of DXR [47] either shields protease-sensitive sites or causes a conformational change of DXR rendering it resistant to chloroplast protease(s), e.g. Clp protease [26], [32]. Thus, fosmidomycin inhibits but also stabilizes the DXR enzyme. "
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    • "Thus, the assembly of photosynthetic complexes and the build-up of thylakoid membranes and plastoglobules in chloroplasts increase the capacity to sequester the newly synthesized carotenoid molecules. Defects in chloroplast development hence result in a decreased accumulation of carotenoids, even under conditions in which an enhanced supply of their isoprenoid precursors is available (Sauret-Güeto et al., 2006; Flores-Perez et al., 2008b). Differentiation of chloroplasts into chromoplasts involves the development of larger plastoglobules and/or carotenoid-sequestering structures of different shapes, allowing the deposition of massive amounts of carotenoids in a matrix of lipoproteins (Deruere et al., 1994; Vishnevetsky et al., 1999; Simkin et al., 2007; Walter and Strack, 2011). "
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    • "In particular, post-transcriptional regulation of DXS could be triggered by key enzymes downstream of the pathway; for example, phytoene synthase (PSY) has been shown to control metabolic flux to the carotenoid pathway (Rodrìguez-Villalòn et al., 2009) and environmental changes (Laule et al., 2003; Wolfertz et al., 2004; Guevara-García et al., 2005; Sauret-Güeto et al., 2006). A multilevel tight regulation of DXS activity seems to be a crucial point of control of this pathway in plants, as DXS, besides affecting chlorophyll content (Mandel el al., 1996), also plays an essential role in chloroplast development during leaf cell maturation (Araki et al., 2000; Flores-Pérez et al., 2008). "
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