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Multicellular organisms regulate cell numbers and cell fate by using asymmetric cell division (ACD) and symmetric cell division (SCD) during their development and to adapt to unfavorable environmental conditions. A stem cell self-renews and generates differentiated cells. In plants, various types of cells are produced by ACD or SCD; however, the molecular mechanisms of ACD or SCD and the cell division mode switch are largely unknown. The moss Physcomitrium (Physcomitrella) patens is a suitable model to study plant stem cells due to its simple anatomy. Here, we report the cell division mode switch induced by abscisic acid (ABA) in P patens. ABA is synthesized in response to abiotic stresses and induces round-shape cells, called brood cells, from cylindrical protonemal cells. Although two daughter cells with distinct sizes were produced by ACD in a protonemal stem cell on ABA-free media, the sizes of two daughter cells became similar with ABA treatment. Actin microfilaments were spatially localized on the apices of apical stem cells in protonemata on ABA-free media, but the polar accumulation was lost under the condition of ABA treatment. Moreover, ABA treatment conferred an identical cell fate to the daughter cells in terms of cell division activity. Collectively, the results indicate ABA may suppress the ACD characteristics but evoke SCD in cells. We also noticed that ABA-induced brood cells not only self-renewed but regenerated protonemal cells when ABA was removed from the media, suggesting that brood cells are novel stein cells that are induced by environmental signals in P. patens.

第37回宇宙環境利用シンポジウム (2023年1月17日-18日. オンライン開催), Space Utilization Research (January 17-18, 2023. Online Meeting), 著者人数: 29名, 資料番号: SA6000180002, F-1

第37回宇宙環境利用シンポジウム (2023年1月17日-18日. オンライン開催), Space Utilization Research (January 17-18, 2023. Online Meeting), 著者人数: 22名ほか, 資料番号: SA6000180007, G-1

第37回宇宙環境利用シンポジウム (2023年1月17日-18日. オンライン開催), Space Utilization Research (January 17-18, 2023. Online Meeting), 著者人数: 19名, 資料番号: SA6000180014, G-8

第37回宇宙環境利用シンポジウム (2023年1月17日-18日. オンライン開催), Space Utilization Research (January 17-18, 2023. Online Meeting), 資料番号: SA6000180013, G-7

Cell-to-cell communication is tightly regulated in response to environmental stimuli in plants. We previously used a photoconvertible fluorescent protein Dendra2 as a model reporter to study this process. This experiment revealed that macromolecular trafficking between protonemal cells in Physcomitrella patens is suppressed in response to abscisic acid (ABA). However, it remains unknown which ABA signaling components contribute to this suppression and how. Here, we show that ABA signaling components SUCROSE NON-FERMENTING 1-RELATED PROTEIN KINASE 2 (PpSnRK2) and ABA INSENSITIVE 3 (PpABI3) play roles as an essential and promotive factor, respectively, in regulating ABA-induced suppression of Dendra2 diffusion between cells (ASD). Our quantitative imaging analysis revealed that disruption of PpSnRK2 resulted in defective ASD onset itself, whereas disruption of PpABI3 caused an 81-min delay in the initiation of ASD. Live-cell imaging of callose deposition using aniline blue staining showed that, despite this onset delay, callose deposition on cross walls remained constant in the PpABI3 disruptant, suggesting that PpABI3 facilitates ASD in a callose-independent manner. Given that ABA is an important phytohormone to cope with abiotic stresses, we further explored cellular physiological responses. We found that the acquisition of salt stress tolerance is promoted by PpABI3 in a quantitative manner similar to ASD. Our results suggest that PpABI3-mediated ABA signaling may effectively coordinate cell-to-cell communication during the acquisition of salt stress tolerance. This study will accelerate the quantitative study for ABA signaling mechanism and function in response to various abiotic stresses.

第36回宇宙環境利用シンポジウム (2022年1月18日-19日. オンライン開催), Space Utilization Research (January 18-19, 2022. Online Meeting), 著者人数: 22名, 資料番号: SA6000168005, G-04

第36回宇宙環境利用シンポジウム (2022年1月18日-19日. オンライン開催), Space Utilization Research (January 18-19, 2022. Online Meeting), 著者人数: 23名ほか, 資料番号: SA6000168002, G-01

第36回宇宙環境利用シンポジウム (2022年1月18日-19日. オンライン開催), Space Utilization Research (January 18-19, 2022. Online Meeting), 著者人数: 24名, 資料番号: SA6000168013, F-01

Mosses are one of the earliest land plants that diverged from fresh-water green algae. They are considered to have acquired a higher capacity for thermal energy dissipation to cope with dynamically changing solar irradiance by utilizing both the "algal-type" light-harvesting complex stress-related (LHCSR)-dependent and the "plant-type" PsbS-dependent mechanisms. It is hypothesized that the formation of photosystem (PS) I and II megacomplex is another mechanism to protect photosynthetic machinery from strong irradiance. Herein, we describe the analysis of the PSI-PSII megacomplex from the model moss, Physcomitrella patens, which was resolved using large-pore clear-native polyacrylamide gel electrophoresis (lpCN-PAGE). The similarity in the migration distance of the Physcomitrella PSI-PSII megacomplex to the Arabidopsis megacomplex shown during lpCN-PAGE suggested that the Physcomitrella PSI-PSII and Arabidopsis megacomplexes have similar structures. Time-resolved chlorophyll fluorescence measurements show that excitation energy was rapidly and efficiently transferred from PSII to PSI, providing evidence of an ordered association of the two photosystems. We also found that LHCSR and PsbS co-migrated with the Physcomitrella PSI-PSII megacomplex. The megacomplex showed pH-dependent chlorophyll fluorescence quenching, which may have been induced by LHCSR and/or PsbS proteins with the collaboration of zeaxanthin. We discuss the mechanism that regulates the energy distribution balance between two photosystems in Physcomitrella.

第35回宇宙環境利用シンポジウム(2021年1月19日-20日. オンライン開催), Space Utilization Research (January 19-20, 2021. Online Meeting), 著者人数: 13名, 資料番号: SA6000156011, レポート番号: G-03

第35回宇宙環境利用シンポジウム(2021年1月19日-20日. オンライン開催), Space Utilization Research (January 19-20, 2021. Online Meeting), 著者人数: 27名, 資料番号: SA6000156002, レポート番号: F-01

第35回宇宙環境利用シンポジウム(2021年1月19日-20日. オンライン開催), Space Utilization Research (January 19-20, 2021. Online Meeting), 著者人数: 15名, 資料番号: SA6000156012, レポート番号: G-04

As pioneer plants mosses are adaptable to extreme environments and are the first to colonize previously uncolonized land. Recently, we designed two centrifuges, MIJ-17 and MK-3, to investigate the effects of long-term cultivation under moderate hypergravity conditions on the growth of mosses. We examined the effects of the vibration generated by these centrifuges on the growth and morphological parameters of the moss Physcomitrella patens, because plants are generally sensitive to vibration. In MIJ-17, random vibration was detected by a micro three-axis acceleration sensor during centrifugation at 2, 5, and 10 G, whereas vibration was negligible in MK-3. Therefore, we compared the growth and morphological parameters of P. patens gametophores cultivated with MIJ-17 and MK-3 at 10 G. The vibration generated by MIJ-17 did not significantly affect the growth and morphological parameters of P. patens gametophores. Thus, we conclude that the vibration of MIJ-17 has a negligible impact on the growth of P. patens gametophores.

第34回宇宙環境利用シンポジウム (2020年1月21日-22日. 宇宙航空研究開発機構宇宙科学研究所(JAXA)(ISAS)), 相模原市, 神奈川県, Space Utilization Research (January 21-22, 2020. Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency(JAXA)(ISAS)), Sagamihara, Kanagawa Japan, 著者人数: 27名, 資料番号: SA6000145015, G-07

第34回宇宙環境利用シンポジウム (2020年1月21日-22日. 宇宙航空研究開発機構宇宙科学研究所(JAXA)(ISAS)), 相模原市, 神奈川県, Space Utilization Research (January 21-22, 2020. Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency(JAXA)(ISAS)), Sagamihara, Kanagawa Japan, 著者人数: 20名, 資料番号: SA6000145014, G-06

Energy dissipation is crucial for land and shallow-water plants exposed to direct sunlight. Almost all green plants dissipate excess excitation energy to protect the photosystem reaction centers, photosystem II (PSII) and photosystem I (PSI), and continue to grow under strong light. In our previous work, we reported that about half of the photosystem reaction centers form a PSI-PSII megacomplex in Arabidopsis thaliana, and that the excess energy was transferred from PSII to PSI fast. However, the physiological function and structure of the megacomplex remained unclear. Here, we suggest that high-light adaptable sun-plants accumulate the PSI-PSII megacomplex more than shade-plants. In addition, PSI of sun-plants has a deep trap to receive excitation energy, which is low-energy chlorophylls showing fluorescence maxima longer than 730 nm. This deep trap may increase the high-light tolerance of PSI by improving excitation energy dissipation. Electron micrographs suggest that one PSII dimer is directly sandwiched between two PSIs with 2-fold rotational symmetry in the basic form of the PSI-PSII megacomplex in green plants. This structure should enable fast energy transfer from PSII to PSI and allow energy in PSII to be dissipated via the deep trap in PSI.

第33回宇宙環境利用シンポジウム (2019年1月24日-25日. 宇宙航空研究開発機構宇宙科学研究所(JAXA)(ISAS)), 相模原市, 神奈川県, Space Utilization Research (January 24-25, 2019. Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency(JAXA)(ISAS)), Sagamihara, Kanagawa Japan, 資料番号: SA6000132008, レポート番号: G-07

第32回宇宙環境利用シンポジウム (2018年1月15日-16日. 宇宙航空研究開発機構宇宙科学研究所(JAXA)(ISAS)), 相模原市, 神奈川県, Space Utilization Research (January 15-16, 2018. Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency(JAXA)(ISAS)), Sagamihara, Kanagawa Japan, 著者人数: 15名, 資料番号: SA6000117010, レポート番号: G-05

第32回宇宙環境利用シンポジウム (2018年1月15日-16日. 宇宙航空研究開発機構宇宙科学研究所(JAXA)(ISAS)), 相模原市, 神奈川県, Space Utilization Research (January 15-16, 2018. Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency(JAXA)(ISAS)), Sagamihara, Kanagawa Japan, 著者人数: 21名, 資料番号: SA6000117008, レポート番号: G-03

第32回宇宙環境利用シンポジウム (2018年1月15日-16日. 宇宙航空研究開発機構宇宙科学研究所(JAXA)(ISAS)), 相模原市, 神奈川県, Space Utilization Research (January 15-16, 2018. Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency(JAXA)(ISAS)), Sagamihara, Kanagawa Japan, 資料番号: SA6000117009, レポート番号: G-04

第31回宇宙環境利用シンポジウム (2017年1月16日-17日. 宇宙航空研究開発機構宇宙科学研究所(JAXA)(ISAS)), 相模原市, 神奈川県, Space Utilization Research (January 16-17, 2017. Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency(JAXA)(ISAS)), Sagamihara, Kanagawa Japan, 資料番号: SA6000061028, レポート番号: SUS31-G13

第31回宇宙環境利用シンポジウム (2017年1月16日-17日. 宇宙航空研究開発機構宇宙科学研究所(JAXA)(ISAS)), 相模原市, 神奈川県, Space Utilization Research (January 16-17, 2017. Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency(JAXA)(ISAS)), Sagamihara, Kanagawa Japan, 資料番号: SA6000061027, レポート番号: SUS31-G12

第30回宇宙環境利用シンポジウム (2016年1月19日-20日. 宇宙航空研究開発機構宇宙科学研究所(JAXA)(ISAS)), 相模原市, 神奈川県, Space Utilization Research (January 19-20, 2016. Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency(JAXA)(ISAS)), Sagamihara, Kanagawa Japan, 資料番号: SA6000048007, レポート番号: G-03

第30回宇宙環境利用シンポジウム (2016年1月19日-20日. 宇宙航空研究開発機構宇宙科学研究所(JAXA)(ISAS)), 相模原市, 神奈川県, Space Utilization Research (January 19-20, 2016. Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency(JAXA)(ISAS)), Sagamihara, Kanagawa Japan, 資料番号: SA6000048045, レポート番号: G-41

第29回宇宙環境利用シンポジウム (2015年1月24日-25日. 宇宙航空研究開発機構宇宙科学研究所(JAXA)(ISAS)), 相模原市, 神奈川県, Space Utilization Research (January 24-25, 2015. Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency(JAXA)(ISAS)), Sagamihara, Kanagawa Japan, 著者人数: 16名, 資料番号: SA6000035009, レポート番号: ISAS-SUR29-S04

第29回宇宙環境利用シンポジウム (2015年1月24日-25日. 宇宙航空研究開発機構宇宙科学研究所(JAXA)(ISAS)), 相模原市, 神奈川県, Space Utilization Research (January 24-25, 2015. Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency(JAXA)(ISAS)), Sagamihara, Kanagawa Japan, 資料番号: SA6000035010, レポート番号: ISAS-SUR29-S05

Vascular plants appeared ~410 million years ago, then diverged into several lineages of which only two survive: the euphyllophytes (ferns and seed plants) and the lycophytes. We report here the genome sequence of the lycophyte Selaginella moellendorffii (Selaginella), the first nonseed vascular plant genome reported. By comparing gene content in evolutionarily diverse taxa, we found that the transition from a gametophyte- to a sporophyte-dominated life cycle required far fewer new genes than the transition from a nonseed vascular to a flowering plant, whereas secondary metabolic genes expanded extensively and in parallel in the lycophyte and angiosperm lineages. Selaginella differs in posttranscriptional gene regulation, including small RNA regulation of repetitive elements, an absence of the trans-acting small interfering RNA pathway, and extensive RNA editing of organellar genes.

We report the draft genome sequence of the model moss Physcomitrella patens and compare its features with those of flowering plants, from which it is separated by more than 400 million years, and unicellular aquatic algae. This comparison reveals genomic changes concomitant with the evolutionary movement to land, including a general increase in gene family complexity; loss of genes associated with aquatic environments (e.g., flagellar arms); acquisition of genes for tolerating terrestrial stresses (e.g., variation in temperature and water availability); and the development of the auxin and abscisic acid signaling pathways for coordinating multicellular growth and dehydration response. The Physcomitrella genome provides a resource for phylogenetic inferences about gene function and for experimental analysis of plant processes through this plant's unique facility for reverse genetics.