Publications by authors named "Yuki Okegawa"

Plants cope with sudden increases in light intensity through various photoprotective mechanisms. Redox regulation by thioredoxin (Trx) systems also contributes to this process. Whereas the functions of f- and m-type Trxs in response to such fluctuating light conditions have been extensively investigated, those of x- and y-type Trxs are largely unknown.

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Redox regulation of chloroplast proteins is necessary to adjust photosynthetic performance with changes in light. The thioredoxin (Trx) system plays a central role in this process. Chloroplast-localized classical Trx is a small redox-active protein that regulates many target proteins by reducing their disulfide bonds in a light-dependent manner.

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Light-dependent activation of chloroplast enzymes is required for the rapid induction of photosynthesis after a shift from dark to light. The thioredoxin (Trx) system plays a central role in this process. In chloroplasts, the Trx system consists of two pathways: the ferredoxin (Fd)/Trx pathway and the nicotinamide adenine dinucleotide phosphate (NADPH)-Trx reductase C (NTRC) pathway.

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The chloroplast-localized cystathionine β-synthase X (CBSX) proteins CBSX1 and CBSX2 have been proposed as modulators of thioredoxins (Trxs). In this study, the contribution of CBSX proteins to the redox regulation of thiol enzymes in the chloroplast Trx system was evaluated both and . The biochemical studies evaluated whether CBSX proteins alter the specificities of classical chloroplastic Trx and Trx for their target proteins.

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In natural habitats, plants have developed sophisticated regulatory mechanisms to optimize the photosynthetic electron transfer rate at the maximum efficiency and cope with the changing environments. Maintaining proper P700 oxidation at photosystem I (PSI) is the common denominator for most regulatory processes of photosynthetic electron transfers. However, the molecular complexes and cofactors involved in these processes and their function(s) have not been fully clarified.

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Plants have a high regeneration capacity and some plant species can regenerate clone plants, called plantlets, from detached vegetative organs. We previously outlined the molecular mechanisms underlying plantlet regeneration from (Brassicaceae) leaf explants. However, the fundamental difference between the plant species that can and cannot regenerate plantlets from vegetative organs remains unclear.

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In addition to linear electron transport, photosystem I cyclic electron transport (PSI-CET) contributes to photosynthesis and photoprotection. In Arabidopsis (), PSI-CET consists of two partially redundant pathways, one of which is the PROTON GRADIENT REGULATION5 (PGR5)/PGR5-LIKE PHOTOSYNTHETIC PHENOTYPE1 (PGRL1)-dependent pathway. Although the physiological significance of PSI-CET is widely recognized, the regulatory mechanism behind these pathways remains largely unknown.

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In response to light, plants efficiently induce photosynthesis. Light activation of thiol enzymes by the thioredoxin (Trx) systems and cyclic electron transport by the PROTON GRADIENT REGULATION5 (PGR5)-dependent pathway contribute substantially to regulation of photosynthesis. Arabidopsis () mutants lacking -type Trxs () show delayed activation of carbon assimilation due to impaired photoreduction of Calvin-Benson cycle enzymes.

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The activity of the molecular motor enzyme, chloroplast ATP synthase, is regulated in a redox-dependent manner. The γ subunit, CF-γ, is the central shaft of this enzyme complex and possesses the redox-active cysteine pair, which is reduced by thioredoxin (Trx). In light conditions, Trx transfers the reducing equivalent obtained from the photosynthetic electron transfer system to the CF-γ.

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Because natural variation in wild species is likely the result of local adaptation, it provides a valuable resource for understanding plant-environmental interactions. Rorippa aquatica (Brassicaceae) is a semi-aquatic North American plant with morphological differences between several accessions, but little information available on any physiological differences. Here, we surveyed the transcriptomes of two R.

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Thioredoxins (Trxs) regulate the activity of target proteins in the chloroplast redox regulatory system. In vivo, a disulfide bond within Trxs is reduced by photochemically generated electrons via ferredoxin (Fd) and ferredoxin-thioredoxin reductase (FTR: EC 1.8.

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Specific antibodies are a reliable tool to examine protein expression patterns and to determine the protein localizations within cells. Generally, recombinant proteins are used as antigens for specific antibody production. However, recombinant proteins from mammals and plants are often overexpressed as insoluble inclusion bodies in Escherichia coli.

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Thioredoxins (Trxs) regulate the activity of various chloroplastic proteins in a light-dependent manner. Five types of Trxs function in different physiological processes in the chloroplast of Arabidopsis thaliana. Previous in vitro experiments have suggested that the f-type Trx (Trx f) is the main redox regulator of chloroplast enzymes, including Calvin cycle enzymes.

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The seamless ligation cloning extract (SLiCE) method is a novel seamless DNA cloning tool that utilizes homologous recombination activities in cell lysates to assemble DNA fragments into a vector. Several laboratory strains can be used as a source for the SLiCE extract; therefore, the SLiCE-method is highly cost-effective.The SLiCE has sufficient cloning ability to support conventional DNA cloning, and can simultaneously incorporate two unpurified DNA fragments into vector.

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Seamless ligation cloning extract (SLiCE) is a simple and efficient method for DNA cloning without the use of restriction enzymes. Instead, SLiCE uses homologous recombination activities from Escherichia coli cell lysates. To date, SLiCE preparation has been performed using an expensive commercially available lytic reagent.

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Plant redox-related proteins were overexpressed using a genetic codon substitution downstream of the translation initiation codon. This method significantly improved recombinant protein expression levels of Arabidopsis chloroplastic thioredoxins and cytosolic nicotinamide adenine dinucleotide phosphate (NADPH)-dependent thioredoxin reductase (E.C.

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Antimycin A3 (AA) is used as an inhibitor of cyclic electron transport around photosystem I. However, the high concentrations of AA that are needed for inhibition have secondary effects, even in chloroplasts. Here, we screened for chemicals that inhibited ferredoxin-dependent plastoquinone reduction in ruptured chloroplasts at lower concentrations than those required for AA.

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In Arabidopsis thaliana, the main route of cyclic electron transport around PSI is sensitive to antimycin A, but the site of inhibition has not been clarified. We discovered that ferredoxin-dependent plastoquinone reduction in ruptured chloroplasts was less sensitive to antimycin A in Arabidopsis that overaccumulated PGR5 (PROTON GRADIENT REGULATION 5) originating from Pinus taeda (PtPGR5) than that in the wild type. Consistent with this in vitro observation, infiltration of antimycin A reduced PSII yields and the non-photochemical quenching (NPQ) of Chl fluorescence in wild-type leaves but not in leaves accumulating PtPGR5.

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The PGR5 (PROTON GRADIENT REGULATION 5) gene that is required for PSI cyclic electron transport in Arabidopsis was knocked down in rice (Oryza sativa). In three PGR5 knockdown (KD) lines, the PGR5 protein level was reduced to 5-8% of that in the wild type, resulting in a 50% reduction in PGRL1 (PGR5-LIKE PHOTOSYNTHETIC PHENOTYPE 1) protein levels. In ruptured chloroplasts, ferredoxin-dependent plastoquinone reduction activity was partially impaired; the phenotype was mimicked by addition of antimycin A to wild-type chloroplasts.

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A significant fraction of a plant's nuclear genome encodes chloroplast-targeted proteins, many of which are devoted to the assembly and function of the photosynthetic apparatus. Using digital video imaging of chlorophyll fluorescence, we isolated proton gradient regulation 7 (pgr7) as an Arabidopsis thaliana mutant with low nonphotochemical quenching of chlorophyll fluorescence (NPQ). In pgr7, the xanthophyll cycle and the PSBS gene product, previously identified NPQ factors, were still functional, but the efficiency of photosynthetic electron transport was lower than in the wild type.

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In addition to linear electron transport from water to NADP(+) , alternative electron transport pathways are believed to regulate photosynthesis. In the two routes of photosystem I (PSI) cyclic electron transport, electrons are recycled from the stromal reducing pool to plastoquinone (PQ), generating additional ΔpH (proton gradient across thylakoid membranes). Plastid terminal oxidase (PTOX) accepts electrons from PQ and transfers them to oxygen to produce water.

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There are at least two photosynthetic cyclic electron transport (CET) pathways in most C(3) plants: the NAD(P)H dehydrogenase (NDH)-dependent pathway and a pathway dependent upon putative ferredoxin:plastoquinone oxidoreductase (FQR) activity. While the NDH complex has been identified, and shown to play a role in photosynthesis, especially under stress conditions, less is known about the machinery of FQR-dependent CET. Recent studies indicate that FQR-dependent CET is dependent upon PGR5, a small protein of unknown function.

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PSI cyclic electron transport is essential for photosynthesis and photoprotection. In higher plants, the antimycin A-sensitive pathway is the main route of electrons in PSI cyclic electron transport. Although a small thylakoid protein, PGR5 (PROTON GRADIENT REGULATION 5), is essential for this pathway, its function is still unclear, and there are numerous debates on the rate of electron transport in vivo and its regulation.

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