The Experts below are selected from a list of 255 Experts worldwide ranked by ideXlab platform
Masahiro Sugiura - One of the best experts on this subject based on the ideXlab platform.
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involvement of a site specific trans acting factor and a common rna binding protein in the editing of Chloroplast mrnas development of a Chloroplast in vitro rna editing system
The EMBO Journal, 2001Co-Authors: Tetsuro Hirose, Masahiro SugiuraAbstract:RNA editing in higher plant Chloroplasts involves C→U conversion at ∼30 specific sites. An in vitro system supporting accurate editing has been developed from tobacco Chloroplasts. Mutational analysis of substrate mRNAs derived from tobacco Chloroplast psbL and ndhB mRNAs confirmed the participation of cis ‐acting elements that had previously been identified in vivo . Competition analysis revealed the existence of site‐specific trans ‐acting factors interacting with the corresponding upstream cis ‐elements. A Chloroplast protein of 25 kDa was found to be specifically associated with the cis ‐element involved in psbL mRNA editing. Immunological analyses revealed that an additional factor, the Chloroplast RNA‐binding protein cp31, is also required for RNA editing at multiple sites. This combination of site‐specific and common RNA‐binding proteins recognizes editing sites in Chloroplasts.
Masanori Izumi - One of the best experts on this subject based on the ideXlab platform.
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Chloroplast Protein Turnover: The Influence of Extraplastidic Processes, Including Autophagy.
International Journal of Molecular Sciences, 2018Co-Authors: Masanori Izumi, Sakuya NakamuraAbstract:: Most assimilated nutrients in the leaves of land plants are stored in Chloroplasts as photosynthetic proteins, where they mediate CO₂ assimilation during growth. During senescence or under suboptimal conditions, Chloroplast proteins are degraded, and the amino acids released during this process are used to produce young tissues, seeds, or respiratory energy. Protein degradation machineries contribute to the quality control of Chloroplasts by removing damaged proteins caused by excess energy from sunlight. Whereas previous studies revealed that Chloroplasts contain several types of intraplastidic proteases that likely derived from an endosymbiosed prokaryotic ancestor of Chloroplasts, recent reports have demonstrated that multiple extraplastidic pathways also contribute to Chloroplast protein turnover in response to specific cues. One such pathway is autophagy, an evolutionarily conserved process that leads to the vacuolar or lysosomal degradation of cytoplasmic components in eukaryotic cells. Here, we describe and contrast the extraplastidic pathways that degrade Chloroplasts. This review shows that diverse pathways participate in Chloroplast turnover during sugar starvation, senescence, and oxidative stress. Elucidating the mechanisms that regulate these pathways will help decipher the relationship among the diverse pathways mediating Chloroplast protein turnover.
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entire photodamaged Chloroplasts are transported to the central vacuole by autophagy
The Plant Cell, 2017Co-Authors: Sakuya Nakamura, Masanori Izumi, Hiroyuki Ishida, Jun HidemaAbstract:Turnover of dysfunctional organelles is vital to maintain homeostasis in eukaryotic cells. As photosynthetic organelles, plant Chloroplasts can suffer sunlight-induced damage. However, the process for turnover of entire damaged Chloroplasts remains unclear. Here, we demonstrate that autophagy is responsible for the elimination of sunlight-damaged, collapsed Chloroplasts in Arabidopsis thaliana . We found that vacuolar transport of entire Chloroplasts, termed chlorophagy, was induced by UV-B damage to the Chloroplast apparatus. This transport did not occur in autophagy-defective atg mutants, which exhibited UV-B-sensitive phenotypes and accumulated collapsed Chloroplasts. Use of a fluorescent protein marker of the autophagosomal membrane allowed us to image autophagosome-mediated transport of entire Chloroplasts to the central vacuole. In contrast to sugar starvation, which preferentially induced distinct type of Chloroplast-targeted autophagy that transports a part of stroma via the Rubisco-containing body (RCB) pathway, photooxidative damage induced chlorophagy without prior activation of RCB production. We further showed that chlorophagy is induced by Chloroplast damage caused by either artificial visible light or natural sunlight. Thus, this report establishes that an autophagic process eliminates entire Chloroplasts in response to light-induced damage.
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autophagy plays a role in Chloroplast degradation during senescence in individually darkened leaves
Plant Physiology, 2008Co-Authors: Shinya Wada, Masanori Izumi, Hiroyuki Ishida, Kohki Yoshimoto, Yoshinori Ohsumi, Amane MakinoAbstract:Chloroplasts contain approximately 80% of total leaf nitrogen and represent a major source of recycled nitrogen during leaf senescence. While bulk degradation of the cytosol and organelles in plants is mediated by autophagy, its role in Chloroplast catabolism is largely unknown. We investigated the effects of autophagy disruption on the number and size of Chloroplasts during senescence. When leaves were individually darkened, senescence was promoted similarly in both wild-type Arabidopsis (Arabidopsis thaliana) and in an autophagy-defective mutant, atg4a4b-1. The number and size of Chloroplasts decreased in darkened leaves of wild type, while the number remained constant and the size decrease was suppressed in atg4a4b-1. When leaves of transgenic plants expressing stroma-targeted DsRed were individually darkened, a large accumulation of fluorescence in the vacuolar lumen was observed. Chloroplasts exhibiting chlorophyll fluorescence, as well as Rubisco-containing bodies, were also observed in the vacuole. No accumulation of stroma-targeted DsRed, Chloroplasts, or Rubisco-containing bodies was observed in the vacuoles of the autophagy-defective mutant. We have succeeded in demonstrating Chloroplast autophagy in living cells and provide direct evidence of Chloroplast transportation into the vacuole.
Tetsuro Hirose - One of the best experts on this subject based on the ideXlab platform.
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involvement of a site specific trans acting factor and a common rna binding protein in the editing of Chloroplast mrnas development of a Chloroplast in vitro rna editing system
The EMBO Journal, 2001Co-Authors: Tetsuro Hirose, Masahiro SugiuraAbstract:RNA editing in higher plant Chloroplasts involves C→U conversion at ∼30 specific sites. An in vitro system supporting accurate editing has been developed from tobacco Chloroplasts. Mutational analysis of substrate mRNAs derived from tobacco Chloroplast psbL and ndhB mRNAs confirmed the participation of cis ‐acting elements that had previously been identified in vivo . Competition analysis revealed the existence of site‐specific trans ‐acting factors interacting with the corresponding upstream cis ‐elements. A Chloroplast protein of 25 kDa was found to be specifically associated with the cis ‐element involved in psbL mRNA editing. Immunological analyses revealed that an additional factor, the Chloroplast RNA‐binding protein cp31, is also required for RNA editing at multiple sites. This combination of site‐specific and common RNA‐binding proteins recognizes editing sites in Chloroplasts.
Tsuneyoshi Kuroiwa - One of the best experts on this subject based on the ideXlab platform.
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Isolation of Chloroplasts and Chloroplast-nuclei(nucleoids)from Chlamydomonas reinhardtii
Plant Morphology, 2020Co-Authors: Atsushi Sakai, Lena Suzuki, Osami Misumi, Tetsuya Higashiyama, Tsuneyoshi KuroiwaAbstract:Summary: We developed a method for isolating Chloroplast-nuclei(nucleoids)from a unicellular green alga, Chlamydomonas reinhardtii, using cell-wall-deficient mutant(cw15)cells. Because the cells drastically change the structure of their Chloroplast-nuclei during the cell division cycle, we synchronized the cell division under a 12: 12-h light: dark regimen, and collected cells in the 8th h during the dark period for use as starting material, when Chloroplast-nuclei were granular in shape and scattered randomly within individual Chloroplasts. The cells were converted to protoplasts and disrupted by repeated passages through a narrow-bore needle, and the intact Chloroplasts were purified by Percoll density-gradient centrifugation. The Chloroplast-nuclei were isolated from the purified Chloroplasts following lysis with Nonidet P-40. The results of Southern and northern hybridization analyses suggested that not only structure, but also DNA synthesis and transcriptional activities of the Chloroplast-nuclei might fluctuate during the cell division cycle of C. reinhardtii. Thus, the Chloroplast-nuclei of C. reinhardtii may provide an ideal system for analyzing the structure-function relationships of DNA-protein complexes.
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a plant specific dynamin related protein forms a ring at the Chloroplast division site
The Plant Cell, 2003Co-Authors: Shin-ya Miyagishima, Tetsuya Higashiyama, Haruko Kuroiwa, Keiji Nishida, Toshiyuki Mori, Motomichi Matsuzaki, Tsuneyoshi KuroiwaAbstract:Chloroplasts have retained the bacterial FtsZ for division, whereas mitochondria lack FtsZ except in some lower eukaryotes. Instead, mitochondrial division involves a dynamin-related protein, suggesting that Chloroplasts retained the bacterial division system, whereas a dynamin-based system replaced the bacterial system in mitochondria during evolution. In this study, we identified a novel plant-specific group of dynamins from the primitive red alga Cyanidioschyzon merolae. Synchronization of Chloroplast division and immunoblot analyses showed that the protein (CmDnm2) associates with the Chloroplast only during division. Immunocytochemical analyses showed that CmDnm2 appears in cytoplasmic patches just before Chloroplast division and is recruited to the cytosolic side of the Chloroplast division site to form a ring in the late stage of division. The ring constricts until division is complete, after which it disappears. These results show that a dynamin-related protein also participates in Chloroplast division and that its behavior differs from that of FtsZ and plastid-dividing rings that form before constriction at the site of division. Combined with the results of a recent study of mitochondrial division in Cyanidioschyzon, our findings led us to hypothesize that when first established in lower eukaryotes, mitochondria and Chloroplasts divided using a very similar system that included the FtsZ ring, the plastid-dividing/mitochondrion-dividing ring, and the dynamin ring.
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aphidicolin uncouples the Chloroplast division cycle from the mitotic cycle in the unicellular red alga cyanidioschyzon merolae
European Journal of Cell Biology, 1996Co-Authors: Ryuuichi Itoh, Haruko Kuroiwa, Hideo Takahashi, Kyoko Toda, Tsuneyoshi KuroiwaAbstract:: The unicellular red alga Cyanidioschyzon merolae possesses one Chloroplast, one mitochondrion, and one cell nucleus. Since the division of these organelles and cytokinesis occur in a coordinated manner, mitosis and the organelle division cycles must be tightly coupled. We report here that aphidicolin, a specific inhibitor of DNA polymerase alpha, uncouples the Chloroplast division cycle from the mitotic cycle. The effects of aphidicolin on C. merolae cells were examined by both epifluorescence and electron microscopy. When cells at the S phase in synchronous culture were treated with aphidicolin, mitosis and cytokinesis did not occur, while Chloroplast division did. Moreover, both of the Chloroplasts in these cells continued to divide and then generated four or more Chloroplasts per cell. The inhibition of cell-nuclear DNA synthesis by aphidicolin was confirmed using microfluorometry. In addition, microfluorometry revealed that the total size and the amount of DNA in Chloroplasts in aphidicolin-treated cells remained constant during uncoupled Chloroplast division. As a result, the size and amount of DNA per Chloroplast decreased stepwise during Chloroplast division. Electron microscopic examination of aphidicolin-treated cells showed that the second division of Chloroplasts uses a Chloroplast-dividing ring similar to that in cells undergoing normal Chloroplast division. These results suggest that Chloroplast division by the dividing ring is free from a checkpoint control that inhibits the progression of mitosis and cytokinesis in the absence of the completion of cell-nuclear DNA synthesis, and also that Chloroplasts lack a checkpoint control mechanism that inhibits its division without growth or DNA synthesis of itself.
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synchronization of Chloroplast division in the ultramicroalga cyanidioschyzon merolae rhodophyta by treatment with light and aphidicolin
Journal of Phycology, 1995Co-Authors: Sachiko Terui, Ryuuichi Itoh, Kuninori Suzuki, Hidenori Takahashi, Tsuneyoshi KuroiwaAbstract:A system of highly synchronized Chloroplast divisions was developed in the unicellular red alga Cyanidioschyzon merolae De Luca, Taddei, & Varano. Chloroplast divisions were examined by epifluorescence microscopy following treatments with light and inhibitors. When the cells during stationary phase were transferred into a new medium under a 12:12 h LD cycle, Chloroplasts, mitochondria, and cell nuclei divided synchronously in that order soon after the initiation of dark periods. More than 40% of the cells contained dividing Chloroplasts. To obtain a system of highly synchronized cell division and Chloroplast division, the cells synchronized by a 12:12 h LD cycle were treated with various inhibitors. Nocodazole and propyzamide did not affect cell and organelle divisions, whereas aphidicolin markedly inhibited cell-nuclear divisions and cytokinesis and induced a delay in Chloroplast division. More than 80% of the cells contained dividing Chloroplasts when cells synchronized by light were treated with aphidicolin for 12 h. This synchronized system will be useful for studies of the molecular and cellular mechanisms of organelle divisions.
Shin-ya Miyagishima - One of the best experts on this subject based on the ideXlab platform.
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Phosphatidylinositol 4-Phosphate Negatively Regulates Chloroplast Division in Arabidopsis
The Plant Cell, 2015Co-Authors: Kumiko Okazaki, Shin-ya Miyagishima, Hajime WadaAbstract:Chloroplast division is performed by the constriction of envelope membranes at the division site. Although constriction of a ring-like protein complex has been shown to be involved in Chloroplast division, it remains unknown how membrane lipids participate in the process. Here, we show that phosphoinositides with unknown function in envelope membranes are involved in the regulation of Chloroplast division in Arabidopsis thaliana. PLASTID DIVISION1 (PDV1) and PDV2 proteins interacted specifically with phosphatidylinositol 4-phosphate (PI4P). Inhibition of phosphatidylinositol 4-kinase (PI4K) decreased the level of PI4P in Chloroplasts and accelerated Chloroplast division. Knockout of PI4Kβ2 expression or downregulation of PI4Kα1 expression resulted in decreased levels of PI4P in Chloroplasts and increased Chloroplast numbers. PI4Kα1 is the main contributor to PI4P synthesis in Chloroplasts, and the effect of PI4K inhibition was largely abolished in the pdv1 mutant. Overexpression of DYNAMIN-RELATED PROTEIN5B (DRP5B), another component of the Chloroplast division machinery, which is recruited to Chloroplasts by PDV1 and PDV2, enhanced the effect of PI4K inhibition, whereas overexpression of PDV1 and PDV2 had additive effects. The amount of DRP5B that associated with Chloroplasts increased upon PI4K inhibition. These findings suggest that PI4P is a regulator of Chloroplast division in a PDV1- and DRP5B-dependent manner.
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Chloroplast DNA replication is regulated by the redox state independently of Chloroplast division in Chlamydomonas reinhardtii.
Plant Physiology, 2013Co-Authors: Yukihiro Kabeya, Shin-ya MiyagishimaAbstract:Chloroplasts arose from a cyanobacterial endosymbiont and multiply by division. In algal cells, Chloroplast division is regulated by the cell cycle so as to occur only once, in the S phase. Chloroplasts possess multiple copies of their own genome that must be replicated during Chloroplast proliferation. In order to examine how Chloroplast DNA replication is regulated in the green alga Chlamydomonas reinhardtii, we first asked whether it is regulated by the cell cycle, as is the case for Chloroplast division. Chloroplast DNA is replicated in the light and not the dark phase, independent of the cell cycle or the timing of Chloroplast division in photoautotrophic culture. Inhibition of photosynthetic electron transfer blocked Chloroplast DNA replication. However, Chloroplast DNA was replicated when the cells were grown heterotrophically in the dark, raising the possibility that Chloroplast DNA replication is coupled with the reducing power supplied by photosynthesis or the uptake of acetate. When dimethylthiourea, a reactive oxygen species scavenger, was added to the photoautotrophic culture, Chloroplast DNA was replicated even in the dark. In contrast, when methylviologen, a reactive oxygen species inducer, was added, Chloroplast DNA was not replicated in the light. Moreover, the Chloroplast DNA replication activity in both the isolated Chloroplasts and nucleoids was increased by dithiothreitol, while it was repressed by diamide, a specific thiol-oxidizing reagent. These results suggest that Chloroplast DNA replication is regulated by the redox state that is sensed by the nucleoids and that the disulfide bonds in nucleoid-associated proteins are involved in this regulatory activity.
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plant specific protein mcd1 determines the site of Chloroplast division in concert with bacteria derived mind
Current Biology, 2009Co-Authors: Hiromitsu Nakanishi, Yukihiro Kabeya, Kenji Suzuki, Shin-ya MiyagishimaAbstract:Summary Chloroplasts evolved from a cyanobacterial endosymbiont [1, 2], and Chloroplast division requires the formation of an FtsZ division ring, which is descended from the cytokinetic machinery of cyanobacteria [3–5]. As in bacteria, the positioning of the Chloroplast FtsZ ring is regulated by the proteins MinD and MinE [3–5]. However, Chloroplast division also involves mechanisms invented by the eukaryotic host cell [6–9]. Here we show that a plant-specific protein MULTIPLE Chloroplast DIVISION SITE 1 (MCD1) regulates FtsZ ring positioning in Arabidopsis thaliana Chloroplasts. Our analyses show that both MCD1 and MinD are required for Chloroplast division, localizing at the division sites and punctate structures dispersed on the inner envelope. MinD overexpression inhibited FtsZ ring formation whereas MCD1 overexpression did not. Localization studies suggest that MCD1 is required for MinD localization to regulate FtsZ ring formation. Furthermore, the interaction between MCD1 and MinD in yeast two-hybrid assays suggests that MCD1 recruits MinD by direct interaction. These results point out differences in the MinD localization mechanism between Chloroplasts and bacterial model systems and suggest that the plant cell evolved a component to modulate the cyanobacteria-derived Min system so as to regulate Chloroplast FtsZ ring positioning.
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Chloroplast biogenesis control of plastid development protein import division and inheritance
The Arabidopsis Book, 2008Co-Authors: Wataru Sakamoto, Shin-ya Miyagishima, Paul JarvisAbstract:The Chloroplast is a multi-copy cellular organelle that not only performs photosynthesis but also synthesizes amino acids, lipids and phytohormones. The plastid also responds to environmental stimuli such as gravitropism. Biogenesis of Chloroplasts is initiated from proplastids in shoot meristems, and involves a series of important events. In the last decade, considerable progress has been made towards understanding various aspects of Chloroplast biogenesis at the molecular level, via studies in model systems such as Arabidopsis. This review focuses on two important aspects of Chloroplast biogenesis, synthesis/assembly and division/transmission. Chloroplasts originated through endosymbiosis from an ancestor of extant cyanobacteria, and thus contain their own genomes. DNA in Chloroplasts is organized into complexes with proteins, and these are called nucleoids. The synthesis of Chloroplast proteins is regulated at various steps. However, a majority of proteins are synthesized in the cytosol, and their proper import into Chloroplast compartments is a prerequisite for Chloroplast development. Fundamental aspects of plastid gene expression/regulation and Chloroplast protein transport are described, together with recent proteome analyses of the organelle. Chloroplasts are not de novo synthesized, but instead are propagated from pre-existing plastids. In addition, plastids are transmitted from generation to generation with a unique mode of inheritance. Our current knowledge on the division machinery and the inheritance of plastids is described.
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a plant specific dynamin related protein forms a ring at the Chloroplast division site
The Plant Cell, 2003Co-Authors: Shin-ya Miyagishima, Tetsuya Higashiyama, Haruko Kuroiwa, Keiji Nishida, Toshiyuki Mori, Motomichi Matsuzaki, Tsuneyoshi KuroiwaAbstract:Chloroplasts have retained the bacterial FtsZ for division, whereas mitochondria lack FtsZ except in some lower eukaryotes. Instead, mitochondrial division involves a dynamin-related protein, suggesting that Chloroplasts retained the bacterial division system, whereas a dynamin-based system replaced the bacterial system in mitochondria during evolution. In this study, we identified a novel plant-specific group of dynamins from the primitive red alga Cyanidioschyzon merolae. Synchronization of Chloroplast division and immunoblot analyses showed that the protein (CmDnm2) associates with the Chloroplast only during division. Immunocytochemical analyses showed that CmDnm2 appears in cytoplasmic patches just before Chloroplast division and is recruited to the cytosolic side of the Chloroplast division site to form a ring in the late stage of division. The ring constricts until division is complete, after which it disappears. These results show that a dynamin-related protein also participates in Chloroplast division and that its behavior differs from that of FtsZ and plastid-dividing rings that form before constriction at the site of division. Combined with the results of a recent study of mitochondrial division in Cyanidioschyzon, our findings led us to hypothesize that when first established in lower eukaryotes, mitochondria and Chloroplasts divided using a very similar system that included the FtsZ ring, the plastid-dividing/mitochondrion-dividing ring, and the dynamin ring.