Chaperones and Proteases

Schroda, Michael; Vallon, Olivier

doi:10.1016/b978-0-12-370873-1.00027-7

Cited by 37 publications

(62 citation statements)

References 266 publications

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“…We also note that both individual cge1 and cge2 null mutants displayed similar slow growth and delayed development phenotypes, which again suggests that these cochaperones do not serve specific Hsp70s. This is not unexpected, as it is usually through the J-domain protein cochaperones that specificity for chaperone substrates is conferred (Schroda and Vallon, 2008;Sharma et al, 2009). Thus, we can anticipate that the low amount of CGE2 still present in the lcge mutant plastids would support only a low activity of all chloroplast Hsp70s, which would in turn be expected to have pleiotropic consequences for chloroplast functions.…”

Section: Discussionmentioning

confidence: 99%

A Stromal Heat Shock Protein 70 System Functions in Protein Import into Chloroplasts in the Moss Physcomitrella patens

2010

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Heat shock protein 70s (Hsp70s) are encoded by a multigene family and are located in different cellular compartments. They have broad-ranging functions, including involvement in protein trafficking, prevention of protein aggregation, and assistance in protein folding. Hsp70s work together with their cochaperones, J domain proteins and nucleotide exchange factors (e.g., GrpEs), in a functional cycle of substrate binding and release accompanied by ATP hydrolysis. We have taken advantage of the gene targeting capability of the moss Physcomitrella patens to investigate the functions of chloroplast Hsp70s. We identified four Hsp70 genes and two GrpE cochaperone homolog genes (CGE) in moss that encode chloroplast proteins. Disruption of one of the Hsp70 genes, that for Hsp70-2, caused lethality, and protein import into heat-shocked chloroplasts isolated from temperature-sensitive hsp70-2 mutants was appreciably impaired. Whereas the double cge null mutant was not viable, we recovered a cge1 null/cge2 knock down mutant in which Hsp70-2 was upregulated. Chloroplasts isolated from this mutant demonstrated a defect in protein import. In addition, two different precursors staged as early import intermediates could be immunoprecipitated with an Hsp70-2-specific antibody. This immunoprecipitate also contained Hsp93 and Tic40, indicating that it represents a precursor still in the Toc/Tic translocon. Together, these data indicate that a stromal Hsp70 system plays a crucial role in protein import into chloroplasts.

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Section: Discussionmentioning

confidence: 99%

A Stromal Heat Shock Protein 70 System Functions in Protein Import into Chloroplasts in the Moss Physcomitrella patens

2010

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“…The C. reinhardtii nuclear genome encodes six members of the FtsH family distributed between the mitochondria (Atteia et al, 2009) and the chloroplast and three FtsH-like proteins (FHL1 to FHL3) that retain a complete AAA+ domain but lack the zinc binding motif (reviewed in Schroda and Vallon, 2009; see phylogenetic tree of FtsH proteins in Supplemental Figure 1). Only two isoforms have been identified in C. reinhardtii thylakoid membranes: FtsH1 (type A) and FtsH2 (type B; Allmer et al, 2006).…”

Section: Discussion the Thylakoid Ftsh Protease Of C Reinhardtii Formentioning

confidence: 99%

“…According to what has been proposed for plant chloroplasts, there could be a joint action of Deg and FtsH proteases in the degradation and repair of D1 upon photoinhibition of C. reinhardtii. Indeed, the set of chloroplast Deg proteases is similar in Arabidopsis (lumenal Deg1, Deg5, and Deg8 and stromal Deg2, Deg6, Deg7, Deg9, and Deg16) and in C. reinhardtii (lumenal Deg1A, Deg1B, Deg1C, Deg5, and Deg8 and stromal Deg2, Deg7, and Deg9;Huesgen et al, 2009;Schroda and Vallon, 2009;Sun et al, 2010). The model of , derived from studies with Arabidopsis, predicts the production of Degdependent fragments whose apparent molecular mass and epitope content match nicely to those we detected with the two distinct D1 antibodies we used (Supplemental Figure 10).…”

Section: Ftsh1 Regulates the Degradation Of Psii By Removing D1 Fragmmentioning

confidence: 99%

Thylakoid FtsH Protease Contributes to Photosystem II and Cytochromeb 6 fRemodeling inChlamydomonas reinhardtiiunder Stress Conditions

et al. 2014

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FtsH is the major thylakoid membrane protease found in organisms performing oxygenic photosynthesis. Here, we show that FtsH from Chlamydomonas reinhardtii forms heterooligomers comprising two subunits, FtsH1 and FtsH2. We characterized this protease using FtsH mutants that we identified through a genetic suppressor approach that restored phototrophic growth of mutants originally defective for cytochrome b 6 f accumulation. We thus extended the spectrum of FtsH substrates in the thylakoid membranes beyond photosystem II, showing the susceptibility of cytochrome b 6 f complexes (and proteins involved in the c i heme binding pathway to cytochrome b 6 ) to FtsH. We then show how FtsH is involved in the response of C. reinhardtii to macronutrient stress. Upon phosphorus starvation, photosynthesis inactivation results from an FtsH-sensitive photoinhibition process. In contrast, we identified an FtsH-dependent loss of photosystem II and cytochrome b 6 f complexes in darkness upon sulfur deprivation. The D1 fragmentation pattern observed in the latter condition was similar to that observed in photoinhibitory conditions, which points to a similar degradation pathway in these two widely different environmental conditions. Our experiments thus provide extensive evidence that FtsH plays a major role in the quality control of thylakoid membrane proteins and in the response of C. reinhardtii to light and macronutrient stress.

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“…The first two proteins are known to interact with each other and Hsp70B is involved in the refolding of stress-denatured proteins, especially under heat shock or high light where it plays a role in protection and photorepair of PSII. In C. reinhardtii, Vipp1 is associated with low density membranes (Zerges and Rochaix, 1998) and thylakoids (Drzymalla et al, 1996), and it is able to form ring-like structures that can assemble into rod-shaped complexes proposed to act as tracks for the transport of lipids or proteins during thylakoid biogenesis (Liu et al, 2005;Schroda and Vallon, 2009). Together with its cochaperone CDJ2, Hsp70B interacts with Vipp1 and may assist in the assembly and disassembly of the Vipp1 ring structures.…”

Section: Conditional Inactivation Of Chloroplast Transcription and Trmentioning

confidence: 99%

Repression of Essential Chloroplast Genes Reveals New Signaling Pathways and Regulatory Feedback Loops inChlamydomonas

et al. 2013

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Although reverse genetics has been used to elucidate the function of numerous chloroplast proteins, the characterization of essential plastid genes and their role in chloroplast biogenesis and cell survival has not yet been achieved. Therefore, we developed a robust repressible chloroplast gene expression system in the unicellular alga Chlamydomonas reinhardtii based mainly on a vitamin-repressible riboswitch, and we used this system to study the role of two essential chloroplast genes: ribosomal protein S12 (rps12), encoding a plastid ribosomal protein, and rpoA, encoding the a-subunit of chloroplast bacterial-like RNA polymerase. Repression of either of these two genes leads to the arrest of cell growth, and it induces a response that involves changes in expression of nuclear genes implicated in chloroplast biogenesis, protein turnover, and stress. This response also leads to the overaccumulation of several plastid transcripts and reveals the existence of multiple negative regulatory feedback loops in the chloroplast gene circuitry.

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Chaperones and Proteases

Cited by 37 publications

References 266 publications

A Stromal Heat Shock Protein 70 System Functions in Protein Import into Chloroplasts in the Moss Physcomitrella patens

A Stromal Heat Shock Protein 70 System Functions in Protein Import into Chloroplasts in the Moss Physcomitrella patens

Thylakoid FtsH Protease Contributes to Photosystem II and Cytochromeb 6 fRemodeling inChlamydomonas reinhardtiiunder Stress Conditions

Repression of Essential Chloroplast Genes Reveals New Signaling Pathways and Regulatory Feedback Loops inChlamydomonas

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