Perturbation of protein homeostasis brings plastids at the crossroad between repairment and dismantling
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ABSTRACT:
ORGANISM(S): Arabidopsis thaliana
PROVIDER: GSE205271 | GEO | 2023/05/26
REPOSITORIES: GEO
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Project description:The chloroplast proteome is a dynamic mosaic of plastid- and nuclear-encoded proteins, and plastid protein homeostasis is maintained through the balance between de novo protein synthesis and proteolysis. Intracellular communication pathways, including the pastid-to-nucleus retrograde communication, and the protein homeostasis machinery shape the chloroplast proteome based on developmental and physiological needs. However, the maintenance of fully functional chloroplasts is costly and under specific stress conditions the degradation of damaged chloroplasts is functional to the maintenance of a heathy population of photosynthesising organelles while promoting nutrient redistribution to sink tissues. In this study, we have addressed this complex regulatory chloroplast quality-control pathway by modulating the expression of two nuclear genes encoding the plastid ribosomal proteins PRPS1 and PRPL4. By transcriptomics, proteomics and transmission electron microscopy analyses, we show that the increased expression of PRPS1 gene leads to chloroplast degradation and early flowering, as an escaping strategy from stress conditions. On the contrary, the overaccumulation of PRPL4 protein is kept under control by the increased accumulation of plastid chaperones and other components of the unfolded protein response (cpUPR) regulatory mechanism. This study advances our understanding of the molecular mechanisms underlying chloroplast retrograde communication and provides new insight into cellular responses to impaired plastid protein homeostasis.
2023-05-12 | PXD034479 | Pride
Project description:Biogenesis of plastid ribosomes is facilitated by auxiliary factors which process and modify ribosomal RNAs (rRNA) or are involved in ribosome assembly. In comparison to their bacterial and mitochondrial counterparts, the biogenesis of plastid ribosomes is less well understood and few auxiliary factors have been described so far. In this study, we report the functional characterization of CGL20 (CONSERVED ONLY IN THE GREEN LINEAGE20) in Arabidopsis thaliana (AtCGL20) a small, proline-rich protein which is targeted to mitochondria and chloroplasts. In Arabidopsis, CGL20 is encoded by segmentally duplicated genes of high similarity (AtCGL20A and AtCGL20B), and inactivation of both in the atcgl20ab mutant leads to a visible virescent phenotype, and growth arrest at low temperature. The chloroplast proteome, thylakoid complex abundance and pigment composition are significantly affected in atcgl20ab mutants, resulting in a combined proton gradient regulation (pgr) and chlororespiratory reduction (crr) phenotype. Loss of AtCGL20 alters plastid rRNA ratios, perturbs the formation of a hidden break in 23S rRNA and causes abnormal accumulation of 50S ribosomal subunits in the high-molecular-mass fraction of chloroplast stromal extracts. Moreover, AtCGL20A-eGFP fusion proteins comigrate with 50S ribosomal subunits in sucrose density gradients, even after RNase treatment of stromal extracts. Therefore, we propose that AtCGL20 participates in late stages of the biogenesis of 50S ribosomal subunits in plastids – a role which presumably evolved in the green lineage as a consequence of structural divergence of plastid ribosomes.
2020-03-16 | GSE134415 | GEO
Project description:Retrograde signaling from the chloroplast to the nucleus is necessary to regulate the chloroplast proteome during development and fluctuating environmental conditions. Although the specific chloroplast process(es) that must occur and the nature of the signal(s) that exits the chloroplast are not well understood, previous studies using drug inhibitors of chloroplast biogenesis have revealed that normal chloroplast development is required to express Photosynthesis Associated Nuclear Genes (PhANGs). In an attempt to determine which specific steps in chloroplast development are involved in retrograde signaling, we analyzed Arabidopsis mutants defective in the six genes encoding sigma factor (Sig) proteins that are utilized by the plastid-encoded RNA polymerase to transcribe specific sets of plastid genes. Here, we demonstrate that both Sig2 and Sig6 have partially redundant roles in not only plastid transcription, but also tetrapyrrole synthesis and retrograde signaling to control PhANG expression. Normal PhANG expression can be partly restored in the sig2 mutant by increasing heme synthesis. Furthermore, there is a genetic interaction between Sig and GUN (genomes uncoupled) genes to generate chloroplast-retrograde signals. These results demonstrate that defective plastid transcription is the source of at least two retrograde signals to the nucleus; one involving tetrapyrrole synthesis and the other involving the accumulation of an unknown plastid transcript. We also propose that the study of sig mutants (with defects in the expression of specific plastid genes) provides a new genetic system, which avoids the use of harsh inhibitors and their potential side effects, to monitor developmental retrograde signaling and to elucidate its mechanisms.
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2012-03-02 | GSE24517 | GEO
Project description:Chloroplast biogenesis represents a crucial step in seedling development, and is essential for the transition to autotrophic growth in plants. This light-controlled process relies on the transcription of nuclear and plastid genomes that drives the effective assembly and regulation of the photosynthetic machinery. Here we reveal a novel regulation level for this process by showing the involvement of chromatin remodelling in the coordination of nuclear and plastid gene expression for proper chloroplast biogenesis and function. The two Arabidopsis homologs of the yeast EPL1 proteins, core components of the NuA4 histone acetyl-transferase complex, are essential for the correct assembly and performance of chloroplasts. EPL1 proteins are necessary for the coordinated expression of nuclear genes encoding most of the components of chloroplast transcriptional machinery, specifically promoting H4K5Ac deposition in these loci. These data unveil a key participation of epigenetic regulatory mechanisms in the coordinated expression of the nuclear and plastid genomes.
2022-07-26 | GSE180614 | GEO
Project description:Upon exposure to light, plant cells quickly acquire photosynthetic competence by converting pale etioplasts into green chloroplasts. This developmental transition involves the de novo biogenesis of the thylakoid system, and requires reprogramming of metabolism and gene expression. Etioplast-to-chloroplast differentiation involves massive changes in plastid ultrastructure, but how these changes are connected to specific changes in physiology, metabolism and expression of the plastid and nuclear genomes is poorly understood. Here a new experimental system in the dicotyledonous model plant tobacco (Nicotiana tabacum) that allows us to study the leaf de-etiolation process at the systems level. We have determined the accumulation kinetics of photosynthetic complexes, pigments, lipids and soluble metabolites, and recorded the dynamic changes in plastid ultrastructure and in the nuclear and plastid transcriptomes. Our data describe the greening process at high temporal resolution, resolve distinct genetic and metabolic phases during de-etiolation, and reveal numerous candidate genes that may be involved in light-induced chloroplast development and thylakoid biogenesis.
2019-03-09 | GSE128049 | GEO
Project description:Chloroplast function requires the coordinated action of nuclear- and chloroplast-derived proteins, including several hundred nuclear-encoded pentatricopeptide repeat (PPR) proteins that regulate plastid mRNA metabolism. Despite their large number and importance, regulatory mechanisms controlling PPR expression are poorly understood. Here we show that the Arabidopsis NOT4A ubiquitin-ligase positively regulates the expression of PROTON GRADIENT REGULATION 3 (PGR3), a PPR protein required for translating several thylakoid-localised photosynthetic components and ribosome subunits within chloroplasts. Loss of NOT4A function leads to a strong depletion of cytochrome b6f and NDH complexes, as well plastid 30S ribosomes, which reduces mRNA translation and negatively impacts photosynthetic capacity, causing pale-yellow and slow-growth phenotypes. Quantitative transcriptome and proteome analyses reveal that PGR3 is misregulated in not4a. We show that the molecular not4a defects mimic those of a pgr3 mutant, and that normal plastid function is restored through transgenic PGR3 expression. Our work identifies NOT4A as crucial for ensuring robust photosynthetic function during development and stress-response, through promoting PGR3 production and chloroplast translation.
2020-11-17 | GSE161571 | GEO
Project description:Biogenesis of plastid ribosomes is assisted by auxiliary factors which process and modify ribosomal RNAs (rRNA) or are involved in ribosome assembly. In comparison to bacterial and mitochondrial ribosomes, plastid ribosome biogenesis is less well understood and only few auxiliary factors have been described, so far. In this study, we report the functional characterization of CGL20 (CONSERVED ONLY IN THE GREEN LINEAGE20) in Arabidopsis thaliana (AtCGL20), a small proline-rich protein targeted to mitochondria and chloroplasts. Its absence is accompanied with a general reduction in chloroplast protein content that leads to a virescent growth phenotype.
2020-02-25 | PXD014514 | Pride
Project description:Regulation of expression of genes encoding chloroplast components is critical to the autotrophic plant and never more so than in the cotyledons of the de-etiolating seedling. Many chloroplast proteins are nuclear-encoded and a retrograde signal from the chloroplasts (the Plastid Signal) modulates nuclear transcription. However, not all chloroplast-targeted genes are subject to this control and not all plastid-dependent nuclear genes are chloroplast-targeted. We therefore aim to provide the most comprehensive screen yet of which genes are affected by plastid-signalling. To specifically knock-out positive plastid signalling in light-grown cotyledons, the herbicide Norflurazon (NF) is supplied in the growth medium, causing a carotenoid deficiency that leaves the chloroplasts vulnerable to photobleaching. This blocks the expression of a subset of nuclear genes, such as Lhcb and HEMA1. Two pairs of RNAs will directly compare the transcription in seedlings grown under continuous white light with and without NF. A third RNA will also be compared from a mutant that shows a degree of constitutive positive plastid signalling. These two mutants act synergistically to counteract the effect of NF on nuclear transcription. The gun1,gun5 double mutant maintains a significantly higher level of Lhcb and HEMA1 expression in the presence of photobeached chloroplasts than the NF-treated wild-type. This transcriptome set will therefore complement RNA1 (wild-type+NF) and indicate which of the genes identified from the RNA1/RNA2 comparison are subject to the particular gun1/gun5 plastid signalling pathway(s). The growth of conditions of the seedlings (namely on MS medium supplemented with 1.5% sucrose, for 3 days under continuous WL following 2 days germination in darkness) has been chosen from the results of our own recent studies using Northern blotting techniques that show these conditions to maximise the respective NF and gun mutant effects on Lhcb and HEMA1 gene expression. This experiment is part one of a two-part study to compare the transcriptional output of this NF-affected pathway with that of a newly discovered FR-mediated pathway. A subsequent array experiment will assess the nuclear response as affected by this FR/ phyA-input pathway and the two sets of array data will be compared and contrasted. Note: Col-0 wild-type (NASC code N1092). gun1,gun5 double mutant(obtained from Enriquez Lopez-Juez, Royal Holloway, University of London.(Mochizuki et al. 2001 PNAS 98: 2053-2058). This line cannot be donated by us as it is the IP of Joanne Chory (SALK Institute, USA). Treatment = a herbicide (Norflurazon) application which leads to chloroplast photobleaching and hence down regulation of nuclear genes dependent on plastid signalling from intact chloroplasts.
2022-11-21 | E-NASC-40 | biostudies-arrayexpress
Project description:Shortly after the release of singlet oxygen (1O2), drastic changes in nuclear gene expression occur in the conditional flu mutant of Arabidopsis that reveal a rapid transfer of signals from the plastid to the nucleus. In contrast to retrograde control of nuclear gene expression by plastid signals described earlier, the primary effect of 1O2 generation in the flu mutant is not the control of chloroplast biogenesis but the activation of a broad range of signaling pathways known to be involved in biotic and abiotic stress responses. This activity of a plastid-derived signal suggests a new function of the chloroplast, namely that of a sensor of environmental changes that activates a broad range of stress responses. Inactivation of the plastid protein EXECUTER1 attenuates the extent of 1O2-induced up-regulation of nuclear gene expression, but it does not fully eliminate these changes. A second related nuclear-encoded protein, dubbed EXECUTER2, has been identified that is also implicated with the signaling of 1O2-dependent nuclear gene expression changes. Like EXECUTER1, EXECUTER2 is confined to the plastid. Inactivation of both EXECUTER proteins in the ex1/ex2/flu triple mutant is sufficient to suppress the up-regulation of almost all 1O2-responsive genes. Retrograde control of 1O2-responsive genes requires the concerted action of both EXECUTER proteins within the plastid compartment. Keywords: biotic and abiotic stress response, nuclear gene expression, plastid-derived signal, Col-0 ecotype, continuous light and then dark-incubated plants
2008-02-14 | GSE10509 | GEO