Table 1.
Putative chloroplast J proteins of Arabidopsis analyzed in this work.
Figure 1.
Nineteen J proteins were imported into chloroplasts.
(A) Fifteen J proteins that were imported into chloroplasts. (B) Chloroplast import of DJC72MM, DJC73MM, DJC31 and DJC62. (C) DJC42 and DJC78MM were not imported into chloroplasts. (D) Chloroplast import of DJC31-G184x. (E) Chloroplast import of DJC62-R180x. In vitro-translated [35S]Met-labeled precursor proteins were incubated with isolated pea chloroplasts under import conditions. Part of the precursor proteins without import (Ivt) or re-isolated intact chloroplasts after import (Chpt) were further treated with thermolysin (Th) or trypsin. Sample for lanes 7 and 10 of (E) were trypsin treated in the presence of 0.1% of Triton X-100. Samples were analyzed by SDS-PAGE followed by fluorography. For each precursor panel, the Ivt lanes (with and without protease treatment) contain the same amount of precursor, and the Chpt lanes contain the same amount of proteins. The Ivt lanes contained 0.9% of the in vitro-translated proteins added to the import reactions shown in the Chpt lanes, except for DJC62, in which the Ivt lanes represent 0.4% of in vitro-translated proteins added to the import reactions. pr, precursor form; m, mature form. m1 and m2, different-sized mature proteins produced after the import of DJC31-G184x and DJC62-R180x. Samples from lane 8 to 10 in (E) were also analyzed by immunoblotting for Toc75 and Tic110 as controls.
Figure 2.
Domain structure and phylogenetic tree of the 19 Arabidopsis chloroplast J proteins.
(A) Schematic representations of domain structures of the 19 Arabidopsis chloroplast J proteins. Each bar is drawn to scale according to the number of amino acids, shown at the bottom. Names of land plant-specific J proteins are written in blue. J, J domain; Gly/Phe-rich, glycine/phenylalanine-rich domain; Zn2+ finger, zinc-finger domain; C-terminal, C-terminal domain; Fd, ferredoxin domain; TRP, tetratricopeptide repeat domain. (B) Phylogenetic relationship of the 19 Arabidopsis chloroplast J proteins. A neighbor-joining tree was constructed using multiple sequence alignments from peptide sequences of the 19 chloroplast J proteins. Bootstrap analyses were computed with 1,000 replicates, and the values of percentage larger than 85 are shown on the branches. Grouping of four clades (shown with gray background) had at least 85% bootstrap support.
Table 2.
Homologs of Arabidopsis chloroplast J protein in other plant species.
Figure 3.
Land plant specific chloroplast J proteins contain highly conserved clade-specific motifs.
Sequence alignments of 6 of the land plant-specific chloroplast J-protein clades. Representative genes (bold typed in Table 2) from each species were aligned. The J domain is underlined with a blue line. The position of the HPD tripeptide is indicated.
Figure 4.
DJC22 proteins from monocots have distinct clade-specific motif from dicots and lower land plants.
Sequence alignments of DJC22 homologs from dicot plants, Selaginella and Physcomitrella, and sequence alignments of DJC22 homologs from monocot plants. Representative genes (bold typed in Table 2) from each species, and homologs from maize (GRMZM2G086841) and sorghum (Sb04g025270) were aligned. The J domain is underlined with a blue line. The position of the HPD tripeptide is indicated.
Figure 5.
Tissue-specific expression patterns of chloroplast J-protein genes in Arabidopsis.
Expression of 17 chloroplast J-protein genes and two cpHsc70s genes in various tissues was retrieved using Genevestigator. Mean values of expression level after normalization were plotted. Land plant-specific J proteins are indicated.
Figure 6.
Regulation of chloroplast J-protein and the two cpHsc70 genes by various abiotic stresses.
Expression ratios (log2 values of stress-treated/controls, as indicated by red and green colored squares) of 17 chloroplast J-protein genes and two cpHsc70 genes under five different stresses in wild-type Arabidopsis were analyzed using Genevestigator. Filters for fold change and p-value were set to>|2| and <0.05, respectively, for consistent stress regulation (marked with open yellow boxes).
Table 3.
Number of Hsp70 and J-protein homologs in various organisms, and in chloroplasts of Arabidopsis and Chlamydomonas.