研究者詳細 - 坂本　亘

論文 - 坂本　亘

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With Greetings and Hope for a Recoverable 2021: From the PCP Editor-In-Chief

Wataru Sakamoto

Plant and Cell Physiology 62 ( 2 ) 219 - 221 2021年5月

Editorial Feature: Meet the PCP Editor-In-Chief—Wataru Sakamoto

Wataru Sakamoto

Plant and Cell Physiology 62 ( 2 ) 222 - 223 2021年5月

Genetic dissection of QTLs associated with spikelet-related traits and grain size in sorghum. 国際誌

Hideki Takanashi, Mitsutoshi Shichijo, Lisa Sakamoto, Hiromi Kajiya-Kanegae, Hiroyoshi Iwata, Wataru Sakamoto, Nobuhiro Tsutsumi

Scientific reports 11 ( 1 ) 9398 - 9398 2021年4月

記述言語：英語掲載種別：研究論文（学術雑誌）

Although spikelet-related traits such as size of anther, spikelet, style, and stigma are associated with sexual reproduction in grasses, no QTLs have been reported in sorghum. Additionally, there are only a few reports on sorghum QTLs related to grain size, such as grain length, width, and thickness. In this study, we performed QTL analyses of nine spikelet-related traits (length of sessile spikelet, pedicellate spikelet, pedicel, anther, style, and stigma; width of sessile spikelet and stigma; and stigma pigmentation) and six grain-related traits (length, width, thickness, length/width ratio, length/thickness ratio, and width/thickness ratio) using sorghum recombinant inbred lines. We identified 36 and 7 QTLs for spikelet-related traits and grain-related traits, respectively, and found that most sorghum spikelet organ length- and width-related traits were partially controlled by the dwarf genes Dw1 and Dw3. Conversely, we found that these Dw genes were not strongly involved in the regulation of grain size. The QTLs identified in this study aid in understanding the genetic basis of spikelet- and grain-related traits in sorghum.

DOI： 10.1038/s41598-021-88917-x

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Phos-tag-based approach to study protein phosphorylation in the thylakoid membrane. 国際誌

Keiji Nishioka, Yusuke Kato, Shin-Ichiro Ozawa, Yuichiro Takahashi, Wataru Sakamoto

Photosynthesis research 147 ( 1 ) 107 - 124 2021年1月

記述言語：英語掲載種別：研究論文（学術雑誌）

Protein phosphorylation is a fundamental post-translational modification in all organisms. In photoautotrophic organisms, protein phosphorylation is essential for the fine-tuning of photosynthesis. The reversible phosphorylation of the photosystem II (PSII) core and the light-harvesting complex of PSII (LHCII) contribute to the regulation of photosynthetic activities. Besides the phosphorylation of these major proteins, recent phosphoproteomic analyses have revealed that several proteins are phosphorylated in the thylakoid membrane. In this study, we utilized the Phos-tag technology for a comprehensive assessment of protein phosphorylation in the thylakoid membrane of Arabidopsis. Phos-tag SDS-PAGE enables the mobility shift of phosphorylated proteins compared with their non-phosphorylated isoform, thus differentiating phosphorylated proteins from their non-phosphorylated isoforms. We extrapolated this technique to two-dimensional (2D) SDS-PAGE for detecting protein phosphorylation in the thylakoid membrane. Thylakoid proteins were separated in the first dimension by conventional SDS-PAGE and in the second dimension by Phos-tag SDS-PAGE. In addition to the isolation of major phosphorylated photosynthesis-related proteins, 2D Phos-tag SDS-PAGE enabled the detection of several minor phosphorylated proteins in the thylakoid membrane. The analysis of the thylakoid kinase mutants demonstrated that light-dependent protein phosphorylation was mainly restricted to the phosphorylation of the PSII core and LHCII proteins. Furthermore, we assessed the phosphorylation states of the structural domains of the thylakoid membrane, grana core, grana margin, and stroma lamella. Overall, these results demonstrated that Phos-tag SDS-PAGE is a useful biochemical tool for studying in vivo protein phosphorylation in the thylakoid membrane protein.

DOI： 10.1007/s11120-020-00803-1

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Phototropin- and photosynthesis-dependent mitochondrial positioning in Arabidopsis thaliana mesophyll cells. 国際誌

Md Sayeedul Islam, Toan Van Nguyen, Wataru Sakamoto, Shingo Takagi

Journal of integrative plant biology 62 ( 9 ) 1352 - 1371 2020年9月

記述言語：英語掲載種別：研究論文（学術雑誌）

Mitochondria are frequently observed in the vicinity of chloroplasts in photosynthesizing cells, and this association is considered necessary for their metabolic interactions. We previously reported that, in leaf palisade cells of Arabidopsis thaliana, mitochondria exhibit blue-light-dependent redistribution together with chloroplasts, which conduct accumulation and avoidance responses under the control of blue-light receptor phototropins. In this study, precise motility analyses by fluorescent microscopy revealed that the individual mitochondria in palisade cells, labeled with green fluorescent protein, exhibit typical stop-and-go movement. When exposed to blue light, the velocity of moving mitochondria increased in 30 min, whereas after 4 h, the frequency of stoppage of mitochondrial movement markedly increased. Using different mutant plants, we concluded that the presence of both phototropin1 and phototropin2 is necessary for the early acceleration of mitochondrial movement. On the contrary, the late enhancement of stoppage of mitochondrial movement occurs only in the presence of phototropin2 and only when intact photosynthesis takes place. A plasma-membrane ghost assay suggested that the stopped mitochondria are firmly adhered to chloroplasts. These results indicate that the physical interaction between mitochondria and chloroplasts is cooperatively mediated by phototropin2- and photosynthesis-dependent signals. The present study might add novel regulatory mechanism for light-dependent plant organelle interactions.

DOI： 10.1111/jipb.12910

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RAD-seq-Based High-Density Linkage Map Construction and QTL Mapping of Biomass-Related Traits in Sorghum using the Japanese Landrace Takakibi NOG.

Hiromi Kajiya-Kanegae, Hideki Takanashi, Masaru Fujimoto, Motoyuki Ishimori, Norikazu Ohnishi, Fiona Wacera W, Everlyne A Omollo, Masaaki Kobayashi, Kentaro Yano, Michiharu Nakano, Toshiaki Kozuka, Makoto Kusaba, Hiroyoshi Iwata, Nobuhiro Tsutsumi, Wataru Sakamoto

Plant & cell physiology 61 ( 7 ) 1262 - 1272 2020年7月

記述言語：英語掲載種別：研究論文（学術雑誌）

Sorghum [Sorghum bicolor (L.) Moench] grown locally by Japanese farmers is generically termed Takakibi, although its genetic diversity compared with geographically distant varieties or even within Takakibi lines remains unclear. To explore the genomic diversity and genetic traits controlling biomass and other physiological traits in Takakibi, we focused on a landrace, NOG, in this study. Admixture analysis of 460 sorghum accessions revealed that NOG belonged to the subgroup that represented Asian sorghums, and it was only distantly related to American/African accessions including BTx623. In an attempt to dissect major traits related to biomass, we generated a recombinant inbred line (RIL) from a cross between BTx623 and NOG, and we constructed a high-density linkage map based on 3,710 single-nucleotide polymorphisms obtained by restriction-site-associated DNA sequencing of 213 RIL individuals. Consequently, 13 fine quantitative trait loci (QTLs) were detected on chromosomes 2, 3, 6, 7, 8 and 9, which included five QTLs for days to heading, three for plant height (PH) and total shoot fresh weight and two for Brix. Furthermore, we identified two dominant loci for PH as being identical to the previously reported dw1 and dw3. Together, these results corroborate the diversified genome of Japanese Takakibi, while the RIL population and high-density linkage map generated in this study will be useful for dissecting other important traits in sorghum.

DOI： 10.1093/pcp/pcaa056

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A 2020 Vision of the Next Four Years—From the PCP’s New Editor-in-Chief

Wataru Sakamoto

Plant and Cell Physiology 61 ( 4 ) 671 - 672 2020年4月

Overexpression of BUNDLE SHEATH DEFECTIVE 2 improves the efficiency of photosynthesis and growth in Arabidopsis. 国際誌

Florian A Busch, Jun Tominaga, Masato Muroya, Norihiko Shirakami, Shunichi Takahashi, Wataru Yamori, Takuya Kitaoka, Sara E Milward, Kohji Nishimura, Erika Matsunami, Yosuke Toda, Chikako Higuchi, Atsuko Muranaka, Tsuneaki Takami, Shunsuke Watanabe, Toshinori Kinoshita, Wataru Sakamoto, Atsushi Sakamoto, Hiroshi Shimada

The Plant journal : for cell and molecular biology 102 ( 1 ) 129 - 137 2020年4月

記述言語：英語掲載種別：研究論文（学術雑誌）

Bundle Sheath Defective 2, BSD2, is a stroma-targeted protein initially identified as a factor required for the biogenesis of ribulose 1,5-bisphosphate carboxylase/oxygenase (RuBisCO) in maize. Plants and algae universally have a homologous gene for BSD2 and its deficiency causes a RuBisCO-less phenotype. As RuBisCO can be the rate-limiting step in CO2 assimilation, the overexpression of BSD2 might improve photosynthesis and productivity through the accumulation of RuBisCO. To examine this hypothesis, we produced BSD2 overexpression lines in Arabidopsis. Compared with wild type, the BSD2 overexpression lines BSD2ox-2 and BSD2ox-3 expressed 4.8-fold and 8.8-fold higher BSD2 mRNA, respectively, whereas the empty-vector (EV) harbouring plants had a comparable expression level. The overexpression lines showed a significantly higher CO2 assimilation rate per available CO2 and productivity than EV plants. The maximum carboxylation rate per total catalytic site was accelerated in the overexpression lines, while the number of total catalytic sites and RuBisCO content were unaffected. We then isolated recombinant BSD2 (rBSD2) from E. coli and found that rBSD2 reduces disulfide bonds using reductants present in vivo, for example glutathione, and that rBSD2 has the ability to reactivate RuBisCO that has been inactivated by oxidants. Furthermore, 15% of RuBisCO freshly isolated from leaves of EV was oxidatively inactivated, as compared with 0% in BSD2-overexpression lines, suggesting that the overexpression of BSD2 maintains RuBisCO to be in the reduced active form in vivo. Our results demonstrated that the overexpression of BSD2 improves photosynthetic efficiency in Arabidopsis and we conclude that it is involved in mediating RuBisCO activation.

DOI： 10.1111/tpj.14617

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応用展開が進みつつある植物ミトコンドリア基礎研究と今後の課題

久保友彦, 有村慎一, 半田裕一, 肥塚信也, 荒河匠, 北崎一義, 風間智彦, 竹中瑞樹, 坂本亘, 石原直忠, 中村崇裕, 新倉聡

育種学研究 22 ( 1 ) 87 - 94 2020年

High temperature causes breakdown of S haplotype-dependent stigmatic self-incompatibility in self-incompatible Arabidopsis thaliana. 国際誌

Masaya Yamamoto, Kenji Nishimura, Hiroyasu Kitashiba, Wataru Sakamoto, Takeshi Nishio

Journal of experimental botany 70 ( 20 ) 5745 - 5751 2019年10月

記述言語：英語掲載種別：研究論文（学術雑誌）

Commercial seeds of Brassicaceae vegetable crops are mostly F1 hybrids, the production of which depends on self-incompatibility during pollination. Self-incompatibility is known to be weakened by exposure to elevated temperatures, which may compromise future breeding and seed production. In the Brassicaceae, self-incompatibility is controlled by two genes, SRK and SCR, which function as female and male determinants of recognition specificity, respectively. However, the molecular mechanisms underlying the breakdown of self-incompatibility under high temperature are poorly understood. In this study, we examined the self-incompatibility phenotypes of self-incompatible Arabidopsis thaliana SRK-SCR transformants under normal (23 °C) and elevated (29 °C) temperatures. Exposure to elevated temperature caused defects in the stigmatic, but not the pollen, self-incompatibility response. In addition, differences in the response to elevated temperature were observed among different S haplotypes. Subcellular localization revealed that high temperature disrupted the targeting of SRK to the plasma membrane. SRK localization in plants transformed with different S haplotypes corresponded to their self-incompatibility phenotypes, further indicating that defects in SRK localization were responsible for the breakdown in the self-incompatibility response at high temperature. Our results provide new insights into the causes of instability in self-incompatibility phenotypes.

DOI： 10.1093/jxb/erz343

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Photosynthetic Responses to High Temperature and Strong Light Suggest Potential Post-flowering Drought Tolerance of Sorghum Japanese Landrace Takakibi.

Norikazu Ohnishi, Fiona Wacera W, Wataru Sakamoto

Plant & cell physiology 60 ( 9 ) 2086 - 2099 2019年9月

記述言語：英語掲載種別：研究論文（学術雑誌）

Sorghum [Sorghum bicolor (L.) Moench] is a C4 crop known to be adaptable to harsh environments such as those under high temperature and water deficit. In this study, we focused on a Japanese sorghum landrace Takakibi (NOG) and employed chlorophyll fluorescence measurements to assess its response to environmental stress. Comparison of photosynthetic rate evaluated using two parameters (effective quantum yield and electron transfer rate) indicated that NOG showed less activity than BTx623 in the pre-flowering stage, which was consistent with the higher susceptibility of NOG seedlings to drought than BTx623. The observed differences in photosynthetic activity between the two cultivars were detectable without drought conditions on days with high temperature and strong light. Interestingly, the photosynthetic activity of NOG leaves in stress conditions increased soon after heading, and the trend was similar to that in BTx642, a well-characterized post-flowering drought-tolerant cultivar. In contrast, BTx623 showed a gradual decline in photosynthetic rate. Thus, we inferred that Japanese Takakibi has the potential to show pre-flowering drought susceptibility and post-flowering drought tolerance, through which it adapts to local climates with high temperature and strong light at harvest.

DOI： 10.1093/pcp/pcz107

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Impaired PSII Proteostasis Promotes Retrograde Signaling via Salicylic Acid. 国際誌

Jianli Duan, Keun Pyo Lee, Vivek Dogra, Siyuan Zhang, Kaiwei Liu, Carlos Caceres-Moreno, Shanshan Lv, Weiman Xing, Yusuke Kato, Wataru Sakamoto, Renyi Liu, Alberto P Macho, Chanhong Kim

Plant physiology 180 ( 4 ) 2182 - 2197 2019年8月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：American Society of Plant Biologists ({ASPB})

Photodamage of the PSII reaction center (RC) is an inevitable process in an oxygen-rich environment. The damaged PSII RC proteins (Dam-PSII) undergo degradation via the thylakoid membrane-bound FtsH metalloprotease, followed by posttranslational assembly of PSII. While the effect of Dam-PSII on gene regulation is described for cyanobacteria, its role in land plants is largely unknown. In this study, we reveal an intriguing retrograde signaling pathway by using the Arabidopsis (Arabidopsis thaliana) yellow variegated2-9 mutant, which expresses a mutated FtsH2 (FtsH2G267D) metalloprotease, specifically impairing its substrate-unfolding activity. This lesion leads to the perturbation of PSII protein homeostasis (proteostasis) and the accumulation of Dam-PSII. Subsequently, this results in an up-regulation of salicylic acid (SA)-responsive genes, which is abrogated by inactivation of either an SA transporter in the chloroplast envelope membrane or extraplastidic SA signaling components as well as by removal of SA. These results suggest that the stress hormone SA, which is mainly synthesized via the chloroplast isochorismate pathway in response to the impaired PSII proteostasis, mediates the retrograde signaling. These findings reinforce the emerging view of chloroplast function toward plant stress responses and suggest SA as a potential plastid factor mediating retrograde signaling.

DOI： 10.1104/pp.19.00483

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Targeted proteome analysis of microalgae under high-light conditions by optimized protein extraction of photosynthetic organisms.

Masakazu Toyoshima, Masumi Sakata, Kazuki Ohnishi, Yuma Tokumaru, Yusuke Kato, Ryutaro Tokutsu, Wataru Sakamoto, Jun Minagawa, Fumio Matsuda, Hiroshi Shimizu

Journal of bioscience and bioengineering 127 ( 3 ) 394 - 402 2019年3月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Elsevier {BV}

Cell disruption and protein solubilization protocols for the relative quantification of individual subunits in photosystems were developed for photosynthetic organisms including cyanobacterium Synechocystis sp. PCC 6803, green-algae Chlamydomonas reinhardtii, and seed plant Arabidopsis thaliana. The optimal methods for the disruption of Chlamydomonas, Synechocystis, and Arabidopsis cells were sonication, microbeads (Φ approximately 0.1 mm), and large beads (Φ = 5.0 mm), respectively. Extraction of the total proteins exceeded 90% using each optimal cell disruption method. Solubilization efficiency of membrane proteins was improved by the phase transfer surfactant (PTS) method. Ninety seven and 114 proteins from Chlamydomonas and Synechocystis, respectively, including membrane proteins such as photosystem proteins, ATP synthase, and NADH dehydrogenase, were successfully analyzed by nano-liquid chromatography tandem mass spectrometry. These results also indicated the improved efficiency of solubilization and trypsin digestion using PTS buffer. The results of the relative quantitative evaluation of photosystem subunits in Chlamydomonas and Synechocystis grown under high-light conditions were consistent with those of previous studies. Thus, the optimal cell disruption and PTS methods allow for comprehensive relative quantitative proteome analysis of photosynthetic organisms. Additionally, NdhD1 and NdhF1, which are NDH-1 subunit homologs, were increased under high-light conditions, suggesting that the NDH-1L complex, including NdhD1 and NdhF1, is increased under high-light conditions. The relative quantitative proteome analysis of individual subunits indicates the diverse functions of NDH-1 protein.

DOI： 10.1016/j.jbiosc.2018.09.001

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Phosphorylation of the Chloroplastic Metalloprotease FtsH in Arabidopsis Characterized by Phos-Tag SDS-PAGE. 国際誌

Yusuke Kato, Wataru Sakamoto

Frontiers in plant science 10 1080 - 1080 2019年

記述言語：英語掲載種別：研究論文（学術雑誌）

FtsH is an essential ATP-dependent metalloprotease for protein quality control in the thylakoid membrane of Arabidopsis thaliana chloroplasts. It is required for chloroplast development during leaf growth, and particularly for the specific degradation of photo-damaged D1 protein in the photosystem II (PSII) complex to maintain photosynthesis activity. In the thylakoid membrane, the reversible phosphorylation of proteins is known to control the activity and remodeling of photosynthetic complexes, and previous studies implicate that FtsH is also phosphorylated. We therefore assessed the phosphorylation status of FtsH and its possible role in the regulatory mechanism in this study. The phosphorylation level of FtsHs that compose the FtsH heterohexameric complex was investigated by phosphate-affinity gel electrophoresis using a Phos-Tag molecule. Phos-tag SDS-PAGE of thylakoid proteins and subsequent immunoblot analysis showed that both type A (FtsH1/5) and type B (FtsH2/8) subunits were separable into phosphorylated and non-phosphorylated forms. Neither different light conditions nor the lack of two major thylakoid kinases, STN7 and STN8, resulted in any clear difference in FtsH phosphorylation, suggesting that this process is independent of the light-dependent regulation of photosynthesis-related proteins. Site-directed mutagenesis of putatively phosphorylated Ser or Thr residues into Ala demonstrated that Ser-212 may play a role in FtsH stability in the thylakoid membranes. Different phosphorylation status of FtsH oligomers analyzed by two-dimensional clear-native/Phos-tag SDS-PAGE implied that phosphorylation partially affects FtsH complex formation or its stability.

DOI： 10.3389/fpls.2019.01080

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Organelle DNA degradation contributes to the efficient use of phosphate in seed plants. 国際誌

Tsuneaki Takami, Norikazu Ohnishi, Yuko Kurita, Shoko Iwamura, Miwa Ohnishi, Makoto Kusaba, Tetsuro Mimura, Wataru Sakamoto

Nature plants 4 ( 12 ) 1044 - 1055 2018年12月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Springer Science and Business Media {LLC}

Mitochondria and chloroplasts (plastids) both harbour extranuclear DNA that originates from the ancestral endosymbiotic bacteria. These organelle DNAs (orgDNAs) encode limited genetic information but are highly abundant, with multiple copies in vegetative tissues, such as mature leaves. Abundant orgDNA constitutes a substantial pool of organic phosphate along with RNA in chloroplasts, which could potentially contribute to phosphate recycling when it is degraded and relocated. However, whether orgDNA is degraded nucleolytically in leaves remains unclear. In this study, we revealed the prevailing mechanism in which organelle exonuclease DPD1 degrades abundant orgDNA during leaf senescence. The DPD1 degradation system is conserved in seed plants and, more remarkably, we found that it was correlated with the efficient use of phosphate when plants were exposed to nutrient-deficient conditions. The loss of DPD1 compromised both the relocation of phosphorus to upper tissues and the response to phosphate starvation, resulting in reduced plant fitness. Our findings highlighted that DNA is also an internal phosphate-rich reservoir retained in organelles since their endosymbiotic origin.

DOI： 10.1038/s41477-018-0291-x

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The Photosystem II Repair Cycle Requires FtsH Turnover through the EngA GTPase 国際誌

Yusuke Kato, Kiwamu Hyodo, Wataru Sakamoto

Plant Physiology 178 ( 2 ) 596 - 611 2018年10月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：American Society of Plant Biologists ({ASPB})

Specific degradation of photodamaged D1, the photosystem II (PSII) reaction center protein, is a crucial step in the PSII repair cycle to maintain photosynthesis activity. Processive proteolysis by the FtsH protease is fundamental to cooperative D1 degradation. Here, we attempted to purify the FtsH complex to elucidate its regulation mechanisms and substrate recognition in Arabidopsis (Arabidopsis thaliana). Unlike previously reported prokaryotic and mitochondrial FtsHs, the Arabidopsis chloroplastic FtsH does not appear to form a megacomplex with prohibition-like proteins but instead accumulates as smaller complexes. The copurified fraction was enriched with a partial PSII intermediate presumably undergoing repair, although its precise properties were not fully clarified. In addition, we copurified a bacteria-type GTPase localized in chloroplasts, EngA, and confirmed its interaction with FtsH by subsequent pull-down and bimolecular fluorescence complementation assays. While the engA mutation is embryo lethal, the transgenic lines overexpressing EngA (EngA-OX) showed leaf variegation reminiscent of the variegated mutant lacking FtsH2. EngA-OX was revealed to accumulate more cleaved D1 fragments and reactive oxygen species than the wild type, indicative of compromised PSII repair. Based on these results and the fact that FtsH becomes more stable in EngA-OX, we propose that EngA negatively regulates FtsH stability. We demonstrate that proper FtsH turnover is crucial for PSII repair in the chloroplasts of Arabidopsis. Consistent with the increased turnover of FtsH under high-light conditions in Chlamydomonas reinhardtii, our findings underline the rapid turnover of not only D1 but also FtsH proteases in the PSII repair cycle.

DOI： 10.1104/pp.18.00652

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VIPP1 Involved in Chloroplast Membrane Integrity Has GTPase Activity in Vitro 国際誌

Norikazu Ohnishi, Lingang Zhang, Wataru Sakamoto

Plant Physiology 177 ( 1 ) 328 - 338 2018年5月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：American Society of Plant Biologists ({ASPB})

VESICLE-INDUCING PROTEIN IN PLASTID1 (VIPP1) is conserved among oxygenic photosynthetic organisms and appears to have diverged from the bacterial PspA protein. VIPP1 localizes to the chloroplast envelope and thylakoid membrane, where it forms homooligomers of high molecular mass. Although multiple roles of VIPP1 have been inferred, including thylakoid membrane formation, envelope maintenance, membrane fusion, and regulation of photosynthetic activity, its precise role in chloroplast membrane quality control remains unknown. VIPP1 forms an oligomer through its amino-terminal domain and triggers membrane fusion in an Mg2+-dependent manner. We previously demonstrated that Arabidopsis (Arabidopsis thaliana) VIPP1 also exhibits dynamic complex disassembly in response to osmotic and heat stresses in vivo. These results suggest that VIPP1 mediates membrane fusion/remodeling in chloroplasts. Considering that protein machines that regulate intracellular membrane fusion/remodeling events often require a capacity for GTP binding and/or hydrolysis, we questioned whether VIPP1 has similar properties. We conducted an in vitro assay using a purified VIPP1-His fusion protein expressed in Escherichia coli cells. VIPP1-His showed GTP hydrolysis activity that was inhibited competitively by an unhydrolyzable GTP analog, GTPγS, and that depends on GTP binding. It is particularly interesting that the ancestral PspA from E. coli also possesses GTP hydrolysis activity. Although VIPP1 does not contain a canonical G domain, the amino-terminal α-helix was found to be important for both GTP binding and GTP hydrolysis as well as for oligomer formation. Collectively, our results reveal that the properties of VIPP1/PspA are similar to those of GTPases.

DOI： 10.1104/pp.18.00145

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Cellular Dynamics: Cellular Systems in the Time Domain. 国際誌

Dan Szymanski, Diane Bassham, Teun Munnik, Wataru Sakamoto

Plant physiology 176 ( 1 ) 12 - 15 2018年1月

Chloroplast DNA Dynamics: Copy Number, Quality Control and Degradation

Sakamoto, Wataru, Takami, Tsuneaki

Plant and Cell Physiology 59 ( 6 ) 1120 - 1127 2018年

記述言語：英語掲載種別：研究論文（学術雑誌）

Endosymbiotically originated chloroplast DNA (cpDNA) encodes part of the genetic information needed to fulfill chloroplast function, including fundamental processes such as photosynthesis. In the last two decades, advances in genome analysis led to the identification of a considerable number of cpDNA sequences from various species. While these data provided the consensus features of cpDNA organization and chloroplast evolution in plants, how cpDNA is maintained through development and is inherited remains to be fully understood. In particular, the fact that cpDNA exists as multiple copies despite its limited genetic capacity raises the important question of how copy number is maintained or whether cpDNA is subjected to quantitative fluctuation or even developmental degradation. For example, cpDNA is abundant in leaves, where it forms punctate structures called nucleoids, which seemingly alter their morphologies and numbers depending on the developmental status of the chloroplast. In this review, we summarize our current understanding of 'cpDNA dynamics', focusing on the changes in DNA abundance. A special focus is given to the cpDNA degradation mechanism, which appears to be mediated by Defective in Pollen organelle DNA degradation 1 (DPD1), a recently discovered organelle exonuclease. The physiological significance of cpDNA degradation in flowering plants is also discussed.

DOI： 10.1093/pcp/pcy084

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Taiwan-Japan Plant Biology 2017 Spotlight Issue: From Light Signals/Signaling to Photosynthesis and Chloroplast Development

Nishimura, Kenji, Matsushita, Tomonao, Shikanai, Toshiharu, Sakamoto, Wataru

Plant and Cell Physiology 59 ( 6 ) 1099 - 1103 2018年

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