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

• Published in: Plant physiology (Bethesda) Vol. 136; no. 4; pp. 4114 - 4126
• Main Authors: Sjogren, L.L.E, MacDonald, T.M, Sutinen, S, Clarke, A.K
• Format: Journal Article
• Language: English
• Published: Rockville, MD American Society of Plant Biologists 01.12.2004; American Society of Plant Physiologists
• Subjects: amino acid sequences; Arabidopsis - genetics; Arabidopsis - growth & development; Arabidopsis - physiology; Arabidopsis Proteins - genetics; Arabidopsis Proteins - physiology; ARABIDOPSIS-THALIANA; ATP-DEPENDENT PROTEASE; Biological and medical sciences; Biological Sciences; Biologiska vetenskaper; Cell Biology and Signal Transduction; Chlorophylls; Chloroplasts; Chloroplasts - genetics; Chloroplasts - metabolism; chlorosis; COMPLEXES; ENVELOPE MEMBRANES; ESCHERICHIA-COLI; Fundamental and applied biological sciences. Psychology; Gene Expression Regulation, Plant; Genotype; heat shock proteins; Heat-Shock Proteins - genetics; Heat-Shock Proteins - physiology; IDENTIFICATION; Imports; knockout mutants; leaf chlorosis; Leaves; Metabolism; Molecular chaperones; Molecular Chaperones - genetics; Molecular Chaperones - physiology; molecular sequence data; mutants; Mutation; NORWAY SPRUCE; nucleotide sequences; Phenotype; Phenotypes; phenotypic variation; photosynthesis; Photosynthesis - genetics; Photosynthesis - physiology; Photosynthesis, respiration. Anabolism, catabolism; photosystem I; photosystem II; plant anatomy; Plant cells; plant growth; Plant Leaves - genetics; Plant Leaves - metabolism; Plant physiology and development; plant proteins; Plants; PROTEINS; REGULATORY SUBUNITS; RNA; RNA-binding proteins; Thylakoids; TRANSLOCATION; ultrastructure; Enzyme; Growth; Adenosinetriphosphatase; RNA binding protein; Ribulose-bisphosphate carboxylase; Lyases; Plant leaf; Arabidopsis thaliana; Chlorosis; Carbon-carbon lyases; Photosystem; Gene; Cruciferae; Carboxy-lyases; Dicotyledones; Angiospermae; Development; Hydrolases; Spermatophyta; Mutation; Photosynthesis; Chloroplast
• ISSN: 0032-0889; 1532-2548
• DOI: 10.1104/pp.104.053835

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.