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Find video protocols related to scientific articles indexed in Pubmed.
Translation-independent circadian control of the cell cycle in a unicellular photosynthetic eukaryote.
Nat Commun
PUBLISHED: 04-04-2014
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Circadian rhythms of cell division have been observed in several lineages of eukaryotes, especially photosynthetic unicellular eukaryotes. However, the mechanism underlying the circadian regulation of the cell cycle and the nature of the advantage conferred remain unknown. Here, using the unicellular red alga Cyanidioschyzon merolae, we show that the G1/S regulator RBR-E2F-DP complex links the G1/S transition to circadian rhythms. Time-dependent E2F phosphorylation promotes the G1/S transition during subjective night and this phosphorylation event occurs independently of cell cycle progression, even under continuous dark or when cytosolic translation is inhibited. Constitutive expression of a phospho-mimic of E2F or depletion of RBR unlinks cell cycle progression from circadian rhythms. These transgenic lines are exposed to higher oxidative stress than the wild type. Circadian inhibition of cell cycle progression during the daytime by RBR-E2F-DP pathway likely protects cells from photosynthetic oxidative stress by temporally compartmentalizing photosynthesis and cell cycle progression.
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DipM is required for peptidoglycan hydrolysis during chloroplast division.
BMC Plant Biol.
PUBLISHED: 02-26-2014
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Chloroplasts have evolved from a cyanobacterial endosymbiont and their continuity has been maintained over time by chloroplast division, a process which is performed by the constriction of a ring-like division complex at the division site. The division complex has retained certain components of the cyanobacterial division complex, which function inside the chloroplast. It also contains components developed by the host cell, which function outside of the chloroplast and are believed to generate constrictive force from the cytosolic side, at least in red algae and Viridiplantae. In contrast to the chloroplasts in these lineages, those in glaucophyte algae possess a peptidoglycan layer between the two envelope membranes, as do cyanobacteria.
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Gamete attachment requires GEX2 for successful fertilization in Arabidopsis.
Curr. Biol.
PUBLISHED: 01-02-2014
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Fertilization requires recognition, attachment, and membrane fusion between gametes. In metazoans, rapidly evolving surface proteins contribute to gamete recognition and adhesion. Flowering plants evolved a double fertilization process wherein two immotile sperm cells are delivered to female gametes by the pollen tube, guided by elaborate communications between male and female reproductive organs. Once released, the sperm cells contact female gametes directly prior to gamete fusion. It remains unclear whether active gamete recognition and attachment mechanisms are required for double fertilization. Here, we provide functional characterization of Arabidopsis GAMETE EXPRESSED 2 (GEX2), which encodes a sperm-expressed protein of unknown function. GEX2 is localized to the sperm membrane and contains extracellular immunoglobulin-like domains, similar to gamete interaction factors in algae and mammals. Using a new in vivo assay, we demonstrate that GEX2 is required for gamete attachment, in the absence of which double fertilization is compromised. Ka/Ks analyses indicate relatively rapid evolution of GEX2, like other proteins involved in male and female interactions. We conclude that surface proteins involved in gamete attachment and recognition exist in plants with immotile gametes, similar to algae and metazoans. This conservation broadens the repertoire of research for plant reproduction factors to mechanisms demonstrated in animals.
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Development of a Heat-Shock Inducible Gene Expression System in the Red Alga Cyanidioschyzon merolae.
PLoS ONE
PUBLISHED: 01-01-2014
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The cell of the unicellular red alga Cyanidioschyzon merolae contains a single chloroplast and mitochondrion, the division of which is tightly synchronized by a light/dark cycle. The genome content is extremely simple, with a low level of genetic redundancy, in photosynthetic eukaryotes. In addition, transient transformation and stable transformation by homologous recombination have been reported. However, for molecular genetic analyses of phenomena that are essential for cellular growth and survival, inducible gene expression/suppression systems are needed. Here, we report the development of a heat-shock inducible gene expression system in C. merolae. CMJ101C, encoding a small heat shock protein, is transcribed only when cells are exposed to an elevated temperature. Using a superfolder GFP as a reporter protein, the 200-bp upstream region of CMJ101C orf was determined to be the optimal promoter for heat-shock induction. The optimal temperature to induce expression is 50°C, at which C. merolae cells are able to proliferate. At least a 30-min heat shock is required for the expression of a protein of interest and a 60-min heat shock yields the maximum level of protein expression. After the heat shock, the mRNA level decreases rapidly. As an example of the system, the expression of a dominant negative form of chloroplast division DRP5B protein, which has a mutation in the GTPase domain, was induced. Expression of the dominant negative DRP5B resulted in the appearance of aberrant-shaped cells in which two daughter chloroplasts and the cells are still connected by a small DRP5B positive tube-like structure. This result suggests that the dominant negative DRP5B inhibited the final scission of the chloroplast division site, but not the earlier stages of division site constriction. It is also suggested that cell cycle progression is not arrested by the impairment of chloroplast division at the final stage.
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FtsZ-less prokaryotic cell division as well as FtsZ- and dynamin-less chloroplast and non-photosynthetic plastid division.
Front Plant Sci
PUBLISHED: 01-01-2014
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The chloroplast division machinery is a mixture of a stromal FtsZ-based complex descended from a cyanobacterial ancestor of chloroplasts and a cytosolic dynamin-related protein (DRP) 5B-based complex derived from the eukaryotic host. Molecular genetic studies have shown that each component of the division machinery is normally essential for normal chloroplast division. However, several exceptions have been found. In the absence of the FtsZ ring, non-photosynthetic plastids are able to proliferate, likely by elongation and budding. Depletion of DRP5B impairs, but does not stop chloroplast division. Chloroplasts in glaucophytes, which possesses a peptidoglycan (PG) layer, divide without DRP5B. Certain parasitic eukaryotes possess non-photosynthetic plastids of secondary endosymbiotic origin, but neither FtsZ nor DRP5B is encoded in their genomes. Elucidation of the FtsZ- and/or DRP5B-less chloroplast division mechanism will lead to a better understanding of the function and evolution of the chloroplast division machinery and the finding of the as-yet-unknown mechanism that is likely involved in chloroplast division. Recent studies have shown that FtsZ was lost from a variety of prokaryotes, many of which lost PG by regressive evolution. In addition, even some of the FtsZ-bearing bacteria are able to divide when FtsZ and PG are depleted experimentally. In some cases, alternative mechanisms for cell division, such as budding by an increase of the cell surface-to-volume ratio, are proposed. Although PG is believed to have been lost from chloroplasts other than in glaucophytes, there is some indirect evidence for the existence of PG in chloroplasts. Such information is also useful for understanding how non-photosynthetic plastids are able to divide in FtsZ-depleted cells and the reason for the retention of FtsZ in chloroplast division. Here we summarize information to facilitate analyses of FtsZ- and/or DRP5B-less chloroplast and non-photosynthetic plastid division.
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Acidophilic green alga Pseudochlorella sp. YKT1 accumulates high amount of lipid droplets under a nitrogen-depleted condition at a low-pH.
PLoS ONE
PUBLISHED: 01-01-2014
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Microalgal storage lipids are considered to be a promising source for next-generation biofuel feedstock. However, microalgal biodiesel is not yet economically feasible due to the high cost of production. One of the reasons for this is that the use of a low-cost open pond system is currently limited because of the unavoidable contamination with undesirable organisms. Extremophiles have an advantage in culturing in an open pond system because they grow in extreme environments toxic to other organisms. In this study, we isolated the acidophilic green alga Pseudochlorella sp. YKT1 from sulfuric acid mine drainage in Nagano Prefecture, Japan. The vegetative cells of YKT1 display the morphological characteristics of Trebouxiophyceae and molecular phylogenetic analyses indicated it to be most closely related to Pseudochlorella pringsheimii. The optimal pH and temperature for the growth of YKT1 are pH 3.0-5.0 and a temperature 20-25°C, respectively. Further, YKT1 is able to grow at pH 2.0 and at 32°C, which corresponds to the usual water temperature in the outdoors in summer in many countries. YKT1 accumulates a large amount of storage lipids (?30% of dry weigh) under a nitrogen-depleted condition at low-pH (pH 3.0). These results show that acidophilic green algae will be useful for industrial applications by acidic open culture systems.
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Single-membrane-bounded peroxisome division revealed by isolation of dynamin-based machinery.
Proc. Natl. Acad. Sci. U.S.A.
PUBLISHED: 05-21-2013
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Peroxisomes (microbodies) are ubiquitous single-membrane-bounded organelles and fulfill essential roles in the cellular metabolism. They are found in virtually all eukaryotic cells and basically multiply by division. However, the mechanochemical machinery involved in peroxisome division remains elusive. Here, we first identified the peroxisome-dividing (POD) machinery. We isolated the POD machinery from Cyanidioschyzon merolae, a unicellular red alga containing a single peroxisome. Peroxisomal division in C. merolae can be highly synchronized by light/dark cycles and the microtubule-disrupting agent oryzalin. By proteomic analysis based on the complete genome sequence of C. merolae, we identified a dynamin-related protein 3 (DRP3) ortholog, CmDnm1 (Dnm1), that predominantly accumulated with catalase in the dividing-peroxisome fraction. Immunofluorescence microscopy demonstrated that Dnm1 formed a ring at the division site of the peroxisome. The outlines of the isolated dynamin rings were dimly observed by phase-contrast microscopy and clearly stained for Dnm1. Electron microscopy revealed that the POD machinery was formed at the cytoplasmic side of the equator. Immunoelectron microscopy showed that the POD machinery consisted of an outer dynamin-based ring and an inner filamentous ring. Down-regulation of Dnm1 impaired peroxisomal division. Surprisingly, the same Dnm1 serially controlled peroxisomal division after mitochondrial division. Because genetic deficiencies of Dnm1 orthologs in multiperoxisomal organisms inhibited both mitochondrial and peroxisomal proliferation, it is thought that peroxisomal division by contraction of a dynamin-based machinery is universal among eukaryotes. These findings are useful for understanding the fundamental systems in eukaryotic cells.
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Defensive bacteriome symbiont with a drastically reduced genome.
Curr. Biol.
PUBLISHED: 04-12-2013
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Diverse insect species harbor symbiotic bacteria, which play important roles such as provisioning nutrients and providing defense against natural enemies [1-6]. Whereas nutritional symbioses are often indispensable for both partners, defensive symbioses tend to be of a facultative nature [1-12]. The Asian citrus psyllid Diaphorina citri is a notorious agricultural pest that transmits Liberibacter spp. (Alphaproteobacteria), causing the devastating citrus greening disease or Huanglongbing [13, 14]. In a symbiotic organ called the bacteriome, D. citri harbors two distinct intracellular symbionts: a putative nutrition provider, Carsonella_DC (Gammaproteobacteria), and an unnamed betaproteobacterium with unknown function [15], for which we propose the name "Candidatus Profftella armatura." Here we report that Profftella is a defensive symbiont presumably of an obligate nature with an extremely streamlined genome. The genomes of Profftella and Carsonella_DC were drastically reduced to 464,857 bp and 174,014 bp, respectively, suggesting their ancient and mutually indispensible association with the host. Strikingly, 15% of the small Profftella genome encoded horizontally acquired genes for synthesizing a novel polyketide toxin. The toxin was extracted, pharmacologically and structurally characterized, and designated diaphorin. The presence of Profftella and its diaphorin-biosynthetic genes was perfectly conserved in the worlds D. citri populations.
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Chloroplast DNA replication is regulated by the redox state independently of chloroplast division in Chlamydomonas reinhardtii.
Plant Physiol.
PUBLISHED: 02-27-2013
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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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Horizontal gene acquisition of liberibacter plant pathogens from a bacteriome-confined endosymbiont of their psyllid vector.
PLoS ONE
PUBLISHED: 01-01-2013
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he Asian citrus psyllid Diaphorina citri is a notorious agricultural pest that transmits the phloem-inhabiting alphaproteobacterial Candidatus Liberibacter asiaticus and allied plant pathogens, which cause the devastating citrus disease called Huanglongbing or greening disease. D. citri harbors two distinct bacterial mutualists in the symbiotic organ called bacteriome: the betaproteobacterium Candidatus Profftella armatura in the syncytial cytoplasm at the center of the bacteriome, and the gammaproteobacterium Candidatus Carsonella ruddii in uninucleate bacteriocytes. Here we report that a putative amino acid transporter LysE of Profftella forms a highly supported clade with proteins of L. asiaticus, L. americanus, and L. solanacearum. L. crescens, the most basal Liberibacter lineage currently known, lacked the corresponding gene. The Profftella-Liberibacter subclade of LysE formed a clade with proteins from betaproteobacteria of the order Burkholderiales, to which Profftella belongs. This phylogenetic pattern favors the hypothesis that the Liberibacter lineage acquired the gene from the Profftella lineage via horizontal gene transfer (HGT) after L. crescens diverged from other Liberibacter lineages. K A/K S analyses further supported the hypothesis that the genes encoded in the Liberibacter genomes are functional. These findings highlight the possible evolutionary importance of HGT between plant pathogens and their insect vectors symbionts that are confined in the symbiotic organ and seemingly sequestered from external microbial populations.
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Structure, regulation, and evolution of the plastid division machinery.
Int Rev Cell Mol Biol
PUBLISHED: 10-25-2011
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Plastids have evolved from a cyanobacterial endosymbiont, and their continuity is maintained by the plastid division and segregation which is regulated by the eukaryotic host cell. Plastids divide by constriction of the inner- and outer-envelope membranes. Recent studies revealed that this constriction is performed by a large protein and glucan complex at the division site that spans the two envelope membranes. The division complex has retained certain components of the cyanobacterial division complex along with components developed by the host cell. Based on the information on the division complex at the molecular level, we are beginning to understand how the division complex has evolved and how it is assembled, constricted, and regulated in the host cell. This chapter reviews the current understanding of the plastid division machinery and some of the questions that will be addressed in the near future.
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Nucleus-independent control of the rubisco operon by the plastid-encoded transcription factor Ycf30 in the red alga Cyanidioschyzon merolae.
Plant Physiol.
PUBLISHED: 09-02-2010
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Chloroplasts originated from a cyanobacterium, which was engulfed by a primitive eukaryotic host cell. During evolution, chloroplasts have largely lost their autonomy due to the loss of many genes from their own genomes. Consequently, expression of genes encoded in the chloroplast genome is mainly controlled by the factors transferred from the cytosol to chloroplasts. However, chloroplast genomes of glaucophytes and red algae have retained some transcription factors (hypothetical chloroplast open reading frame 27 to 30 [Ycf27-Ycf30]) that are absent from green algae and land plants. Here, we show that the red algal chloroplast up-regulates transcription of the Rubisco operon rbcLS-cbbX via Ycf30 independently of nuclear control. Light-induced transcriptional activation of the Rubisco operon was observed in chloroplasts isolated from the red alga Cyanidioschyzon merolae. The activation was suppressed by 3-(3,4-dichlorophenyl)-1,1-dimethylurea. These results suggest that chloroplast autonomously regulates transcription of the Rubisco operon in response to the activation of photosynthesis driven by the light. Transcriptional activation of the Rubisco operon was specifically repressed by the addition of anti-Ycf30 antibodies. Furthermore, reduced NADP, ribulose-1,5-bisphosphate, and 3-phosphoglyceric acid triggered the up-regulation of Rubisco transcription in the dark, and the activation was dependent on Ycf30. Thus, red algal chloroplasts have retained a nucleus-independent transcriptional regulation of the Rubisco operon to respond to environmental changes. The autonomous system would have been necessary for the initial fixation of cyanobacterial photosynthesis in the ancient nonphotosynthetic eukaryotic host. It has remained functional in the red algal chloroplast over evolutionary time.
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Chloroplast division: squeezing the photosynthetic captive.
Curr. Opin. Microbiol.
PUBLISHED: 08-01-2010
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Chloroplasts have evolved from a cyanobacterial endosymbiont and have been retained in eukaryotic cells for more than one billion years via chloroplast division and inheritance by daughter cells during cell division. Recent studies revealed that chloroplast division is performed by a large protein complex at the division site, encompassing both the inside and the outside of the two envelope membranes. The division complex has retained a few components of the cyanobacterial division complex to go along with other components supplied by the host cell. On the basis of the information about the division complex, we are beginning to understand how the division complex evolved, and how eukaryotic host cells regulate chloroplast division during proliferation and differentiation.
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The YlmG protein has a conserved function related to the distribution of nucleoids in chloroplasts and cyanobacteria.
BMC Plant Biol.
PUBLISHED: 04-02-2010
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Reminiscent of their free-living cyanobacterial ancestor, chloroplasts proliferate by division coupled with the partition of nucleoids (DNA-protein complexes). Division of the chloroplast envelope membrane is performed by constriction of the ring structures at the division site. During division, nucleoids also change their shape and are distributed essentially equally to the daughter chloroplasts. Although several components of the envelope division machinery have been identified and characterized, little is known about the molecular components/mechanisms underlying the change of the nucleoid structure.
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Bacterial genes in the aphid genome: absence of functional gene transfer from Buchnera to its host.
PLoS Genet.
PUBLISHED: 02-26-2010
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Genome reduction is typical of obligate symbionts. In cellular organelles, this reduction partly reflects transfer of ancestral bacterial genes to the host genome, but little is known about gene transfer in other obligate symbioses. Aphids harbor anciently acquired obligate mutualists, Buchnera aphidicola (Gammaproteobacteria), which have highly reduced genomes (420-650 kb), raising the possibility of gene transfer from ancestral Buchnera to the aphid genome. In addition, aphids often harbor other bacteria that also are potential sources of transferred genes. Previous limited sampling of genes expressed in bacteriocytes, the specialized cells that harbor Buchnera, revealed that aphids acquired at least two genes from bacteria. The newly sequenced genome of the pea aphid, Acyrthosiphon pisum, presents the first opportunity for a complete inventory of genes transferred from bacteria to the host genome in the context of an ancient obligate symbiosis. Computational screening of the entire A. pisum genome, followed by phylogenetic and experimental analyses, provided strong support for the transfer of 12 genes or gene fragments from bacteria to the aphid genome: three LD-carboxypeptidases (LdcA1, LdcA2,psiLdcA), five rare lipoprotein As (RlpA1-5), N-acetylmuramoyl-L-alanine amidase (AmiD), 1,4-beta-N-acetylmuramidase (bLys), DNA polymerase III alpha chain (psiDnaE), and ATP synthase delta chain (psiAtpH). Buchnera was the apparent source of two highly truncated pseudogenes (psiDnaE and psiAtpH). Most other transferred genes were closely related to genes from relatives of Wolbachia (Alphaproteobacteria). At least eight of the transferred genes (LdcA1, AmiD, RlpA1-5, bLys) appear to be functional, and expression of seven (LdcA1, AmiD, RlpA1-5) are highly upregulated in bacteriocytes. The LdcAs and RlpAs appear to have been duplicated after transfer. Our results excluded the hypothesis that genome reduction in Buchnera has been accompanied by gene transfer to the host nuclear genome, but suggest that aphids utilize a set of duplicated genes acquired from other bacteria in the context of the Buchnera-aphid mutualism.
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Eukaryotic and eubacterial contributions to the establishment of plastid proteome estimated by large-scale phylogenetic analyses.
Mol. Biol. Evol.
PUBLISHED: 11-12-2009
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Plastids including chloroplasts arose from a cyanobacterial endosymbiont and have retained their own genome, but the size has been reduced to less than one-tenth of the original bacterial genome. Over time, genes essential to plastid function have been transferred from the ancestral plastid genome to the nucleus, and the gene products are now targeted into the plastid from the host cytosol. However, phylogenetic analyses have suggested that the functions of certain original proteins encoded by the endosymbiont genome have been replaced by nucleus-encoded proteins of noncyanobacterial origin and that several proteins have been newly added to maintain and control plastids. In order to evaluate the rate and origin of noncyanobacterial proteins that have contributed to the establishment of the plastid proteome, we performed phylogenetic analyses of plastid-targeted proteins that are shared by the red alga Cyanidioschyzon merolae (455 proteins) and the Viridiplanta Arabidopsis thaliana (744 proteins). Our results show that approximately 40% of the plastid proteome common to red algae and green plants originated from genes of both the ancestral eukaryotic host and various lineages of bacteria (eubacteria) other than cyanobacteria. The replacement or addition of components was frequently observed for most of the plastid functions except for the light reaction of photosynthesis and the translation and degradation of proteins in the plastid. These results suggest that a considerable amount of bacterial metagenomic material, as well as the genomes of the host and the endosymbiont, has contributed to the establishment of the plastid before the split of the red and green algae.
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The PLASTID DIVISION1 and 2 components of the chloroplast division machinery determine the rate of chloroplast division in land plant cell differentiation.
Plant Cell
PUBLISHED: 06-30-2009
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In most algae, the chloroplast division rate is held constant to maintain the proper number of chloroplasts per cell. By contrast, land plants evolved cell and chloroplast differentiation systems in which the size and number of chloroplasts change along with their respective cellular function by regulation of the division rate. Here, we show that PLASTID DIVISION (PDV) proteins, land plant-specific components of the division apparatus, determine the rate of chloroplast division. Overexpression of PDV proteins in the angiosperm Arabidopsis thaliana and the moss Physcomitrella patens increased the number but decreased the size of chloroplasts; reduction of PDV levels resulted in the opposite effect. The level of PDV proteins, but not other division components, decreased during leaf development, during which the chloroplast division rate also decreased. Exogenous cytokinins or overexpression of the cytokinin-responsive transcription factor CYTOKININ RESPONSE FACTOR2 increased the chloroplast division rate, where PDV proteins, but not other components of the division apparatus, were upregulated. These results suggest that the integration of PDV proteins into the division machinery enabled land plant cells to change chloroplast size and number in accord with the fate of cell differentiation.
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PARC6, a novel chloroplast division factor, influences FtsZ assembly and is required for recruitment of PDV1 during chloroplast division in Arabidopsis.
Plant J.
PUBLISHED: 05-02-2009
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Chloroplast division in plant cells is accomplished through the coordinated action of the tubulin-like FtsZ ring inside the organelle and the dynamin-like ARC5 ring outside the organelle. This coordination is facilitated by ARC6, an inner envelope protein required for both assembly of FtsZ and recruitment of ARC5. Recently, we showed that ARC6 specifies the mid-plastid positioning of the outer envelope proteins PDV1 and PDV2, which have parallel functions in dynamin recruitment. PDV2 positioning involves direct ARC6-PDV2 interaction, but PDV1 and ARC6 do not interact indicating that an additional factor functions downstream of ARC6 to position PDV1. Here, we show that PARC6 (paralog of ARC6), an ARC6-like protein unique to vascular plants, fulfills this role. Like ARC6, PARC6 is an inner envelope protein with its N-terminus exposed to the stroma and Arabidopsis parc6 mutants exhibit defects of chloroplast and FtsZ filament morphology. However, whereas ARC6 promotes FtsZ assembly, PARC6 appears to inhibit FtsZ assembly, suggesting that ARC6 and PARC6 function as antagonistic regulators of FtsZ dynamics. The FtsZ inhibitory activity of PARC6 may involve its interaction with the FtsZ-positioning factor ARC3. A PARC6-GFP fusion protein localizes both to the mid-plastid and to a single spot at one pole, reminiscent of the localization of ARC3, PDV1 and ARC5. Although PARC6 localizes PDV1, it is not required for PDV2 localization or ARC5 recruitment. Our findings indicate that PARC6, like ARC6, plays a role in coordinating the internal and external components of the chloroplast division complex, but that PARC6 has evolved distinct functions in the division process.
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Conservation and differences of the Min system in the chloroplast and bacterial division site placement.
Commun Integr Biol
PUBLISHED: 04-16-2009
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Chloroplasts are descended from a cyanobacterial endosymbiont and divide by binary fission. Reminiscent of the process in their bacterial ancestor, chloroplast division involves a part of cyanobacteria-derived division machineries in addition to those acquired during chloroplast evolution.1,2 In both bacterial and chloroplast division, formation of the FtsZ ring at the mid position is required for subsequent constriction and fission at the mid division site.1-4 As in bacteria, positioning of the FtsZ ring at the mid-chloroplast is mediated by the Min system.1,2 Recently, we identified the MCD1 protein, a plant-specific component of the Min system in Arabidopsis thaliana chloroplasts.5 Unlike other division components that have been acquired after endosymbiosis and function outside of the chloroplasts (i.e., in/on the outer envelope membrane),6-9 MCD1 functions inside the chloroplast. Since we already discussed about the function and significance of MCD1 as a division component of plant origin,5 here we focus on and discuss about the diversity and evolution of the Min system.
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Plant-specific protein MCD1 determines the site of chloroplast division in concert with bacteria-derived MinD.
Curr. Biol.
PUBLISHED: 01-08-2009
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Chloroplasts evolved from a cyanobacterial endosymbiont, and chloroplast division requires the formation of an FtsZ division ring, which is descended from the cytokinetic machinery of cyanobacteria. As in bacteria, the positioning of the chloroplast FtsZ ring is regulated by the proteins MinD and MinE. However, chloroplast division also involves mechanisms invented by the eukaryotic host cell. 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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Plastid chaperonin proteins Cpn60 alpha and Cpn60 beta are required for plastid division in Arabidopsis thaliana.
BMC Plant Biol.
PUBLISHED: 01-06-2009
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Plastids arose from a free-living cyanobacterial endosymbiont and multiply by binary division as do cyanobacteria. Plastid division involves nucleus-encoded homologs of cyanobacterial division proteins such as FtsZ, MinD, MinE, and ARC6. However, homologs of many other cyanobacterial division genes are missing in plant genomes and proteins of host eukaryotic origin, such as a dynamin-related protein, PDV1 and PDV2 are involved in the division process. Recent identification of plastid division proteins has started to elucidate the similarities and differences between plastid division and cyanobacterial cell division. To further identify new proteins that are required for plastid division, we characterized previously and newly isolated plastid division mutants of Arabidopsis thaliana.
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Analysis of gamete membrane dynamics during double fertilization of Arabidopsis.
J. Plant Res.
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Angiosperms have a unique sexual reproduction system called "double fertilization." One sperm cell fertilizes the egg and another sperm cell fertilizes the central cell. To date, plant gamete membrane dynamics during fertilization has been poorly understood. To analyze this unrevealed gamete subcellular behavior, live cell imaging analyses of Arabidopsis double fertilization were performed. We produced female gamete membrane marker lines in which fluorescent proteins conjugated with PIP2a finely visualized egg cell and central cell surfaces. Using those lines together with a sperm cell membrane marker line expressing GCS1-GFP, the double fertilization process was observed. As a result, after gamete fusion, putative sperm plasma membrane GFP signals were occasionally detected on the egg cell surface adjacent to the central cell. In addition, time-lapse imaging revealed that GCS1-GFP signals entered both the egg cell and the central cell in parallel with the sperm cell movement toward the female gametes during double fertilization. These findings suggested that the gamete fusion process based on membrane dynamics was composed of (1) plasma membrane fusion on male and female gamete surfaces, (2) entry of sperm internal membrane components into the female gametes, and (3) plasmogamy.
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The plastid-dividing machinery: formation, constriction and fission.
Curr. Opin. Plant Biol.
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Plastids divide by constriction of the plastid-dividing (PD) machinery, which encircles the division site. The PD machinery consists of the stromal inner machinery which includes the inner PD and filamenting temperature-sensitive mutant Z (FtsZ) rings and the cytosolic outer machinery which includes the outer PD and dynamin rings. The major constituent of the PD machinery is the outer PD ring, which consists of a bundle of polyglucan filaments. In addition, recent proteomic studies suggest that the PD machinery contains additional proteins that have not been characterized. The PD machinery forms from the inside to the outside of the plastid. The constriction seems to occur by sliding of the polyglucan filaments of the outer PD ring, aided by dynamin. The final fission of the plastid is probably promoted by the pinchase activity of dynamin.
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Expression of the nucleus-encoded chloroplast division genes and proteins regulated by the algal cell cycle.
Mol. Biol. Evol.
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Chloroplasts have evolved from a cyanobacterial endosymbiont and their continuity has been maintained by chloroplast division, which is performed by the constriction of a ring-like division complex at the division site. It is believed that the synchronization of the endosymbiotic and host cell division events was a critical step in establishing a permanent endosymbiotic relationship, such as is commonly seen in existing algae. In the majority of algal species, chloroplasts divide once per specific period of the host cell division cycle. In order to understand both the regulation of the timing of chloroplast division in algal cells and how the system evolved, we examined the expression of chloroplast division genes and proteins in the cell cycle of algae containing chloroplasts of cyanobacterial primary endosymbiotic origin (glaucophyte, red, green, and streptophyte algae). The results show that the nucleus-encoded chloroplast division genes and proteins of both cyanobacterial and eukaryotic host origin are expressed specifically during the S phase, except for FtsZ in one graucophyte alga. In this glaucophyte alga, FtsZ is persistently expressed throughout the cell cycle, whereas the expression of the nucleus-encoded MinD and MinE as well as FtsZ ring formation are regulated by the phases of the cell cycle. In contrast to the nucleus-encoded division genes, it has been shown that the expression of chloroplast-encoded division genes is not regulated by the host cell cycle. The endosymbiotic gene transfer of minE and minD from the chloroplast to the nuclear genome occurred independently on multiple occasions in distinct lineages, whereas the expression of nucleus-encoded MIND and MINE is regulated by the cell cycle in all lineages examined in this study. These results suggest that the timing of chloroplast division in algal cell cycle is restricted by the cell cycle-regulated expression of some but not all of the chloroplast division genes. In addition, it is suggested that the regulation of each division-related gene was established shortly after the endosymbiotic gene transfer, and this event occurred multiple times independently in distinct genes and in distinct lineages.
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