Inactivation of the <i>clpC1</i> Gene Encoding a Chloroplast Hsp100 Molecular Chaperone Causes Growth Retardation, Leaf Chlorosis, Lower Photosynthetic Activity, and a Specific Reduction in Photosystem Content

Sjögren, Lars; MacDonald, Tara M.; Sutinen, Sirkka; Clarke, Adrian K.

doi:10.1104/pp.104.053835

Cited by 132 publications

(151 citation statements)

References 56 publications

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“…2, A and B), strongly supporting the notion that the homozygous genotypes were responsible for seed abortion. Identification of two independent mutant alleles that give rise to the same phenotype is widely accepted as proof of a causal relationship (Sjö gren et al, 2004;Baldwin et al, 2005;Puyaubert et al, 2008). Thus, our data provide very strong evidence of an essential role for AtOEP80.…”

Section: Inactivation Of Atoep80 Causes Seed Abortionsupporting

confidence: 56%

The Omp85-Related Chloroplast Outer Envelope Protein OEP80 Is Essential for Viability in Arabidopsis

et al. 2008

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b-Barrel proteins of the Omp85 (Outer membrane protein, 85 kD) superfamily exist in the outer membranes of Gram-negative bacteria, mitochondria, and chloroplasts. Prominent Omp85 proteins in bacteria and mitochondria mediate biogenesis of other b-barrel proteins and are indispensable for viability. In Arabidopsis (Arabidopsis thaliana) chloroplasts, there are two distinct types of Omp85-related protein: Toc75 (Translocon at the outer envelope membrane of chloroplasts, 75 kD) and OEP80 (Outer Envelope Protein, 80 kD). Toc75 functions as a preprotein translocation channel during chloroplast import, but the role of OEP80 remains elusive. We characterized three T-DNA mutants of the Arabidopsis OEP80 (AtOEP80) gene. Selectable markers associated with the oep80-1 and oep80-2 insertions segregated abnormally, suggesting embryo lethality of the homozygous genotypes. Indeed, no homozygotes were identified among .100 individuals, and heterozygotes of both mutants produced approximately 25% aborted seeds upon self-pollination. Embryo arrest occurred at a relatively late stage (globular embryo proper) as revealed by analysis using Nomarski optics microscopy. This is substantially later than arrest caused by loss of the principal Toc75 isoform, atToc75-III (two-cell stage), suggesting a more specialized role for AtOEP80. Surprisingly, the oep80-3 T-DNA (located in exon 1 between the first and second ATG codons of the open reading frame) did not cause any detectable developmental defects or affect the size of the AtOEP80 protein in chloroplasts. This indicates that the N-terminal region of AtOEP80 is not essential for the targeting, biogenesis, or functionality of the protein, in contrast with atToc75-III, which requires a bipartite targeting sequence.

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Section: Inactivation Of Atoep80 Causes Seed Abortionsupporting

confidence: 56%

The Omp85-Related Chloroplast Outer Envelope Protein OEP80 Is Essential for Viability in Arabidopsis

et al. 2008

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“…As would be expected for substrates whose degradation was impaired, most of the identified proteins accumulated in the clpP6 antisense lines relative to the wild type. The three high molecular mass substrates were also more abundant in an Arabidopsis clpC1 mutant, in which the level of the likely chaperone partner to the Clp proteolytic core, ClpC, was reduced by ;65% (Sjö gren et al, 2004). Moreover, most of the identified protein substrates were more abundant in younger leaves of wild-type plants than in mature leaves, probably because the developing chloroplasts in younger leaves are more metabolically active, with higher rates of transcription, translation, and protein turnover.…”

Section: Discussionmentioning

confidence: 73%

Structural and Functional Insights into the Chloroplast ATP-Dependent Clp Protease in Arabidopsis

et al. 2006

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In contrast with the model Escherichia coli Clp protease, the ATP-dependent Clp protease in higher plants has a remarkably diverse proteolytic core consisting of multiple ClpP and ClpR paralogs, presumably arranged within a dual heptameric ring structure. Using antisense lines for the nucleus-encoded ClpP subunit, ClpP6, we show that the Arabidopsis thaliana Clp protease is vital for chloroplast development and function. Repression of ClpP6 produced a proportional decrease in the Clp proteolytic core, causing a chlorotic phenotype in young leaves that lessened upon maturity. Structural analysis of the proteolytic core revealed two distinct subcomplexes that likely correspond to single heptameric rings, one containing the ClpP1 and ClpR1-4 proteins, the other containing ClpP3-6. Proteomic analysis revealed several stromal proteins more abundant in clpP6 antisense lines, suggesting that some are substrates for the Clp protease. A proteolytic assay developed for intact chloroplasts identified potential substrates for the stromal Clp protease in higher plants, most of which were more abundant in young Arabidopsis leaves, consistent with the severity of the chlorotic phenotype observed in the clpP6 antisense lines. The identified substrates all function in more general housekeeping roles such as plastid protein synthesis, folding, and quality control, rather than in metabolic activities such as photosynthesis.

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“…However, our data indicate that even the hsp93V mutant, which shows protein-import defects, degrades GS2 normally. The mutant also shows normal degradation of the mistargeted 33-kD protein of the oxygen-evolving complex OEC33, another potential substrate of the ClpP protease (Sjö gren et al, 2004). Therefore, functional evidence for Hsp93 involvement in ClpP protease activity in higher plant chloroplasts is not yet available.…”

Section: Discussionmentioning

confidence: 97%

“…Interestingly, although Hsp93 was not detected in the ClpP core complex isolated from chloroplasts, the land plant chloroplast ClpP complex contains two additional peripheral subunits, ClpT1 and ClpT2 (previously named ClpS1 and ClpS2), that have high sequence similarity to the N-terminal portion of Hsp93 (Peltier et al, 2004). Hsp93 may also be involved in the biogenesis of photosystems (Sjö gren et al, 2004), regulating chlorophyll b biosynthesis (Nakagawara et al, 2007), iron homeostasis (Wu et al, 2010), and antagonizing the function of the VAR2 protease (Park and Rodermel, 2004). It cannot, therefore, be excluded that the pale-green and protein import-defective phenotypes of hsp93V mutants are secondary effects due to the reduction of these other functions.…”

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confidence: 99%

The Amino-Terminal Domain of Chloroplast Hsp93 Is Important for Its Membrane Association and Functions in Vivo

Chu

2012

Plant Physiology

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Chloroplast 93-kD heat shock protein (Hsp93/ClpC), an Hsp100 family member, is suggested to have various functions in chloroplasts, including serving as the regulatory chaperone for the ClpP protease in the stroma and acting as a motor component of the protein translocon at the envelope. Indeed, although Hsp93 is a soluble stromal protein, a portion of it is associated with the inner envelope membrane. The mechanism and functional significance of this Hsp93 membrane association have not been determined. Here, we mapped the region important for Hsp93 membrane association by creating various deletion constructs and found that only the construct with the amino-terminal domain deleted, Hsp93-DN, had reduced membrane association. When transformed into Arabidopsis (Arabidopsis thaliana), most atHsp93V-DN proteins did not associate with membranes and atHsp93V-DN failed to complement the pale-green and protein import-defective phenotypes of an hsp93V knockout mutant. The residual atHsp93V-DN at the membranes had further reduced association with the central protein translocon component Tic110. However, the degradation of chloroplast glutamine synthetase, a potential substrate for the ClpP protease, was not affected in the hsp93V mutant or in the atHSP93V-DN transgenic plants. Hsp93-DN also had the same ATPase activity as that of full-length Hsp93. These data suggest that the association of Hsp93 with the inner envelope membrane through its amino-terminal domain is important for the functions of Hsp93 in vivo.Chloroplasts are structurally complex organelles that perform diverse functions (Leister, 2003;Block et al., 2007). They are composed of three membranes, the outer and inner envelope membranes and the thylakoid membranes, and these membranes enclose three aqueous compartments, the intermembrane space, stroma, and thylakoid lumen. Although chloroplasts have their own genome, most chloroplast proteins are encoded by the nuclear genome and are translated in the cytosol as a precursor protein with an N-terminal extension called the transit peptide. Transit peptides direct the import of proteins into chloroplasts through the translocon complex located in the chloroplast envelope. Translocon components of the outer membrane are called Toc (for translocon at the outer envelope membrane of chloroplasts) proteins and those in the inner envelope membrane are called Tic (for translocon at the inner envelope membrane of chloroplasts) proteins. Three Toc components, Toc159, Toc34, and Toc75, form the Toc core complex. Toc159 and Toc34 function as receptors that recognize the precursors targeting to chloroplasts. Toc75 forms a protein-conducting channel across the outer membrane. Three proteins, Tic20, Tic21, and Tic110, have been suggested to function as the channel for precursor translocation across the inner membrane. Tic110 has also been shown to function as the stromal-side receptor for transit peptides and as a scaffold for assembling other stromal translocon components. Tic40 is a cochaperone that coordinates the actions of...

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Inactivation of the clpC1 Gene Encoding a Chloroplast Hsp100 Molecular Chaperone Causes Growth Retardation, Leaf Chlorosis, Lower Photosynthetic Activity, and a Specific Reduction in Photosystem Content

Cited by 132 publications

References 56 publications

The Omp85-Related Chloroplast Outer Envelope Protein OEP80 Is Essential for Viability in Arabidopsis

The Omp85-Related Chloroplast Outer Envelope Protein OEP80 Is Essential for Viability in Arabidopsis

Structural and Functional Insights into the Chloroplast ATP-Dependent Clp Protease in Arabidopsis

The Amino-Terminal Domain of Chloroplast Hsp93 Is Important for Its Membrane Association and Functions in Vivo

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