Chloroplasts Have a Novel Cpn10 in Addition to Cpn20 as Co-chaperonins in Arabidopsis thaliana

Koumoto, Yasuko; Shimada, Tomoo; Kondo, Maki; Hara‐Nishimura, Ikuko; Nishimura, Mikio

doi:10.1074/jbc.m102330200

Cited by 49 publications

(45 citation statements)

References 28 publications

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“…Northern blot analysis reveals that CPN10 transcript accumulates in leaves and stems but not in roots (Koumoto et al, 2001). Data from our microarray, RT-PCR, and ChIP analyses indicate that CIA2 directly binds to and regulates the expression of CPN10.…”

Section: Discussionmentioning

confidence: 89%

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CIA2 Coordinately Up-Regulates Protein Import and Synthesis in Leaf Chloroplasts

2009

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Plastid biogenesis and maintenance depend on the coordinated assembly of proteins imported from the cytosol with proteins translated within plastids. Chloroplasts in leaf cells have a greater need for protein import and protein synthesis than plastids in other organs due to the large amount of proteins required for photosynthesis. We previously reported that the Arabidopsis (Arabidopsis thaliana) transcription factor CIA2 specifically up-regulates leaf expression of genes encoding protein translocons Toc33 and Toc75, which are essential for protein import into chloroplasts. Protein import efficiency was therefore reduced in cia2 mutant chloroplasts. To further understand the function of CIA2, gene expression profiles of the wild type and a cia2 mutant were compared by microarray analysis. Interestingly, in addition to genes encoding protein translocon components, other genes down-regulated in cia2 almost exclusively encode chloroplast ribosomal proteins. Isolated cia2 mutant chloroplasts showed reduced translation efficiency and steady-state accumulation of plastid-encoded proteins. When CIA2 was ectopically expressed in roots, expression of both the protein translocon and ribosomal protein genes increased. Further analyses in vivo revealed that CIA2 up-regulated these genes by binding directly to their promoter regions. We propose that CIA2 is an important factor responsible for fulfilling the higher protein demands of leaf chloroplasts by coordinately increasing both protein import and protein translation efficiencies.

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Section: Discussionmentioning

confidence: 89%

“…CPN10 is homologous to GroES of Escherichia coli and also functions as a chloroplast protein folding cochaperonin (Koumoto et al, 2001). Northern blot analysis reveals that CPN10 transcript accumulates in leaves and stems but not in roots (Koumoto et al, 2001).…”

Section: Discussionmentioning

confidence: 99%

CIA2 Coordinately Up-Regulates Protein Import and Synthesis in Leaf Chloroplasts

2009

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“…Cpn21 was characterized as a 21-kDa protein chaperonin 21 (Cpn21), which is a functional homolog of the chaperonin 10 (Cpn10) and consists of two Cpn 10-like domains fused together in tandem (Hirohashi et al, 1999). Also named Cpn20 (TAIR, The Arabidopsis Information Resource), Cpn21 seems to work independently of a chloroplast Cpn10 (both are homologues of the E. coli GroEs) on the regulation of specific Cpn60 subunit homologues (E. coli GroEl homologues) in plastids (Koumoto et al, 2001). In Arabidopsis, the expression of the chloroplast Cpn10 in mature plants is detected only in leaves and stems, while Cpn20 is expressed in leaves, stems and roots (Koumoto et al, 1999 and.…”

Section: Protective Factors Of Macromoleculesmentioning

confidence: 99%

In silico analysis of ESTs from roots of Rangpur lime (Citrus limonia Osbeck) under water stress

et al. 2007

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CitEST project resulted in the construction of cDNA libraries from different Citrus sp. tissues under various physiological conditions. Among them, plantlets of Rangpur lime were exposed to hydroponic conditions with and without water stress using PEG6000. RNA from roots was obtained and generated a total of 4,130 valid cDNA reads, with 2,020 from the non-stressed condition and 2,110 from the stressed set. Bioinformatic analyses measured the frequency of each read in the libraries and yielded an in silico transcriptional profile for each condition. A total of 40 contigs were differentially expressed and allowed to detect up-regulated homologue sequences to well known genes involved in stress response, such as aquaporins, dehydrin, sucrose synthase, and proline-related synthase. Some sequences could not be classified by using FunCat and remained with an unknown function. A large number of sequences presented high similarities to annotated genes involved with cell energy, protein synthesis and cellular transport, suggesting that Rangpur lime may sustain active cell growth under stressed condition. The presence of membrane transporters and cell signaling components could be an indication of a coordinated morphological adaptation and biochemical response during drought, helping to explain the higher tolerance of this rootstock to water stress.

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“…Proteins destined for the two endosymbiotic organelles (i.e., plastids and mitochondria) are targeted from the cytoplasm as unfolded precursors (Keegstra and Froehlich, 1999;Koumoto et al, 2001;Jarvis and Soll, 2002;Soll and Schleiff, 2004;Jarvis, 2008). In the cytosol, unfolded proteins have a high tendency to form cytotoxic, life-threatening, and nonspecific aggregates if they accumulate to high levels (Wickner et al, 1999;Esser et al, 2004;Meredith, 2005;Kabashi and Durham, 2006).…”

Section: Introductionmentioning

confidence: 99%

Heat Shock Protein Cognate 70-4 and an E3 Ubiquitin Ligase, CHIP, Mediate Plastid-Destined Precursor Degradation through the Ubiquitin-26S Proteasome System inArabidopsis

et al. 2009

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Plastid-targeted proteins pass through the cytosol as unfolded precursors. If proteins accumulate in the cytosol, they can form nonspecific aggregates that cause severe cellular damage. Here, we demonstrate that high levels of plastid precursors are degraded through the ubiquitin-proteasome system (UPS) in Arabidopsis thaliana cells. The cytosolic heat shock protein cognate 70-4 (Hsc70-4) and E3 ligase carboxy terminus of Hsc70-interacting protein (CHIP) were highly induced in plastid protein import2 plants, which had a T-DNA insertion at Toc159 and showed an albino phenotype and a severe defect in protein import into chloroplasts. Hsc70-4 and CHIP together mediated plastid precursor degradation when import-defective chloroplast-targeted reporter proteins were transiently expressed in protoplasts. Hsc70-4 recognized specific sequence motifs in transit peptides and thereby led to precursor degradation through the UPS. CHIP, which interacted with Hsc70-4, functioned as an E3 ligase in the Hsc70-4-mediated protein degradation. The physiological role of Hsc70-4 was confirmed by analyzing Hsc70-4 RNA interfernce plants in an hsc70-1 mutant background. Plants with lower Hsc70 levels exhibited abnormal embryogenesis, resulting in defective seedlings that displayed high levels of reactive oxygen species and monoubiquitinated Lhcb4 precursors. We propose that Hsc70-4 and CHIP mediate plastid-destined precursor degradation to prevent cytosolic precursor accumulation and thereby play a critical role in embryogenesis. INTRODUCTIONProteins destined for the two endosymbiotic organelles (i.e., plastids and mitochondria) are targeted from the cytoplasm as unfolded precursors (Keegstra and Froehlich, 1999;Koumoto et al., 2001;Jarvis and Soll, 2002;Soll and Schleiff, 2004;Jarvis, 2008). In the cytosol, unfolded proteins have a high tendency to form cytotoxic, life-threatening, and nonspecific aggregates if they accumulate to high levels (Wickner et al., 1999;Esser et al., 2004;Meredith, 2005;Kabashi and Durham, 2006). Therefore, posttranslational targeting to endosymbiotic organelles requires that precursor levels be maintained within limits that do not result in nonspecific aggregate formation. At the same time, the cytosolic regulatory mechanism must not jeopardize the supply of sufficient amounts of proteins to the organelles.Eukaryotic cells have a protein quality control (PQC) mechanism to constantly monitor the quality of newly synthesized proteins and preexisting proteins and to actively remove unfolded or misfolded proteins (Hartl and Hayer-Hartl, 2002;Hatakeyama and Nakayama, 2003;Esser et al., 2004). It is reported that as much as 30% of newly synthesized proteins are immediately degraded by the PQC system because of a problem in protein folding (Schubert et al., 2000). The PQC in the cytosol is achieved by two opposing processes: chaperone-assisted folding and ubiquitin/proteasome-mediated degradation. The molecular chaperones heat shock protein 70 (Hsp70) and heat shock protein cognate 70 (Hsc70), whose levels are ele...

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Chloroplasts Have a Novel Cpn10 in Addition to Cpn20 as Co-chaperonins in Arabidopsis thaliana

Cited by 49 publications

References 28 publications

CIA2 Coordinately Up-Regulates Protein Import and Synthesis in Leaf Chloroplasts

CIA2 Coordinately Up-Regulates Protein Import and Synthesis in Leaf Chloroplasts

In silico analysis of ESTs from roots of Rangpur lime (Citrus limonia Osbeck) under water stress

Heat Shock Protein Cognate 70-4 and an E3 Ubiquitin Ligase, CHIP, Mediate Plastid-Destined Precursor Degradation through the Ubiquitin-26S Proteasome System inArabidopsis

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