A mutant impaired in the production of plastome-encoded proteins uncovers a mechanism for the homeostasis of isoprenoid biosynthetic enzymes in Arabidopsis plastids.
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.
Flores-Pérez
Ursula
U
Departament de Genètica Molecular de Plantes, Centre for Research on Agricultural Genomics, 08034 Barcelona, Spain.
Sauret-Güeto
Susanna
S
Gas
Elisabet
E
Jarvis
Paul
P
Rodríguez-Concepción
Manuel
M
D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure; D029681:Arabidopsis Proteins / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D002736:Chloroplasts / Q000235:genetics / Q000378:metabolism / Q000648:ultrastructure; D018548:Cotyledon / Q000235:genetics / Q000378:metabolism / Q000648:ultrastructure; D006706:Homeostasis; D046529:Microscopy, Electron, Transmission; D008969:Molecular Sequence Data; D009154:Mutation; D009569:Nitric Oxide / Q000378:metabolism; D019001:Nitric Oxide Synthase / Q000235:genetics / Q000378:metabolism*; D010802:Phylogeny; D030821:Plants, Genetically Modified; D018087:Plastids / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*; D012270:Ribosomes / Q000378:metabolism; D036226:Seedlings / Q000235:genetics / Q000378:metabolism / Q000648:ultrastructure; D015398:Signal Transduction / Q000235:genetics / Q000502:physiology; D013403:Sugar Phosphates / Q000378:metabolism; D013729:Terpenes / Q000378:metabolism; D014158:Transcription, Genetic
D029681:Arabidopsis Proteins; D013403:Sugar Phosphates; D013729:Terpenes; D009569:Nitric Oxide; C521947:NOA1 protein, Arabidopsis; D019001:Nitric Oxide Synthase