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- Clarke, Adrian K, 1964, et al.
(författare)
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The ATP-dependent Clp protease in chloroplasts of higher plants
- 2005
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Ingår i: Physiologia Plantarum. - : Wiley. - 0031-9317 .- 1399-3054. ; 123:4, s. 406-412
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Tidskriftsartikel (refereegranskat)abstract
- The best-known proteases in plastids are those that belong to families common to eubacteria. One of the first identified was the ATP-dependent caseinolytic protease (Clp), whose structure and function have been well characterized in Escherichia coli. Plastid Clp proteins in higher plants are surprisingly numerous and diverse, with at least 16 distinct Clp proteins in the model plant Arabidopsis thaliana. Multiple paralogues exist for several of the different types of plastid Clp protein, with the most extreme being five for the proteolytic subunit ClpP. Both biochemical and genetic studies have recently begun to reveal the intricate structural interactions between the various Clp proteins, and their importance for chloroplast function and plant development. Much of the recent data suggests that the function of many of the Clp proteins probably affects more specific processes within chloroplasts, in addition to the more general 'housekeeping' role previously assumed.
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| 2. |
- Sjögren, Lars, 1977, et al.
(författare)
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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
- 2004
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Ingår i: Plant Physiology. - : Oxford University Press (OUP). - 0032-0889 .- 1532-2548. ; 136:4, s. 4114-4126
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Tidskriftsartikel (refereegranskat)abstract
- ClpC is a molecular chaperone of the Hsp100 family. In higher plants there are two chloroplast-localized paralogs (ClpC1 and ClpC2) that are approximately 93% similar in primary sequence. In this study, we have characterized two independent Arabidopsis (Arabidopsis thaliana) clpC1 T-DNA insertion mutants lacking on average 65% of total ClpC content. Both mutants display a retarded-growth phenotype, leaves with a homogenous chlorotic appearance throughout all developmental stages, and more perpendicular secondary influorescences. Photosynthetic performance was also impaired in both knockout lines, with relatively fewer photosystem I and photosystem II complexes, but no changes in ATPase and Rubisco content. However, despite the specific drop in photosystem I and photosystem II content, no changes in leaf cell anatomy or chloroplast ultrastructure were observed in the mutants compared to the wild type. Previously proposed functions for envelope-associated ClpC in chloroplast protein import and degradation of mistargeted precursors were examined and shown not to be significantly impaired in the clpC1 mutants. In the stroma, where the majority of ClpC protein is localized, marked increases of all ClpP paralogs were observed in the clpC1 mutants but less variation for the ClpR paralogs and a corresponding decrease in the other chloroplast-localized Hsp100 protein, ClpD. Increased amounts of other stromal molecular chaperones (Cpn60, Hsp70, and Hsp90) and several RNA-binding proteins were also observed. Our data suggest that overall ClpC as a stromal molecular chaperone plays a vital role in chloroplast function and leaf development and is likely involved in photosystem biogenesis.
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| 5. |
- Zheng, Bo, et al.
(författare)
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A nuclear-encoded ClpP subunit of the chloroplast ATP-dependent Clp protease is essential for early development in Arabidopsis thaliana
- 2006
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Ingår i: Planta. - : Springer Science and Business Media LLC. - 0032-0935 .- 1432-2048. ; 224:5, s. 1103-1115
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Tidskriftsartikel (refereegranskat)abstract
- ClpP4 is a nuclear-encoded plastid protein that functions as a proteolytic subunit of the ATP-dependent Clp protease of higher plants. Given the lack of viable clpP4 knockout mutants, antisense clpP4 repression lines were prepared to study the functional importance of ClpP4 in Arabidopsis thaliana. Screening of transformants revealed viable lines with up to 90% loss of wild type levels of ClpP4 protein, while those with > 90% were severely bleached and strongly retarded in vegetative growth, failing to reach reproductive maturity. Of the viable antisense plants, repression of clpP4 expression produced a pleiotropic phenotype, of which slow growth and leaf variegation were most prominent. Chlorosis was most severe in younger leaves, with the affected regions localized around the mid-vein and exhibiting impaired chloroplast development and mesophyll cell differentiation. Chlorosis lessened during leaf expansion until all had regained the wild type appearance upon maturity. This change in phenotype correlated with the developmental expression of ClpP4 in the wild type, in which ClpP4 was less abundant in mature leaves due to post-transcriptional/translational regulation. Repression of ClpP4 caused a concomitant down-regulation of other nuclear-encoded ClpP paralogs in the antisense lines, but no change in other chloroplast-localized Clp proteins. Greening of the young chlorotic antisense plants upon maturation was accelerated by increased light, either by longer photoperiod or by higher growth irradiance; conditions that both raised levels of ClpP4 in wild type leaves. In contrast, shift to low growth irradiance decreased the relative amount of ClpP4 in wild type leaves, and caused newly developed leaves of fully greened antisense lines to regain the chlorotic phenotype.
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