Itoh Ryuichi



Associate Professor

Researcher Number(JSPS Kakenhi)


Current Affiliation Organization 【 display / non-display

  • Duty   University of the Ryukyus   Faculty of Science   Chemistry, Biology and Marine Science   Associate Professor  

  • Charge of Lecture   University of the Ryukyus   Graduate School of Engineering and Science   Marine and Environmental Sciences   Associate Professor  

  • Charge of Lecture   University of the Ryukyus   Graduate School of Engineering and Science   Chemistry, Biology and Marine Science   Associate Professor  

External Career 【 display / non-display

  • 2005.04

    University of the Ryukyus, Faculty of Science, Department of Chemistry, Biology, and Marine Science, Cell and Functional Biology, Associate Professor  

Research Interests 【 display / non-display

  • Plant Cell Biology

  • Plant Cell Biology

  • 植物の細胞生物学

Research Areas 【 display / non-display

  • Life Science / Plant molecular biology and physiology

  • Life Science / Plant molecular biology and physiology

Research Theme 【 display / non-display

  • Replication and Morphogenesis of Plastids

Published Papers 【 display / non-display

  • TGD5 is required for normal morphogenesis of non-mesophyll plastids, but not mesophyll chloroplasts, in Arabidopsis

    Itoh R.D.

    Plant Journal ( Plant Journal )  107 ( 1 ) 237 - 255   2021.07 [ Peer Review Accepted ]

    Type of publication: Research paper (scientific journal)

     View Summary

    Stromules are dynamic membrane-bound tubular structures that emanate from plastids. Stromule formation is triggered in response to various stresses and during plant development, suggesting that stromules may have physiological and developmental roles in these processes. Despite the possible biological importance of stromules and their prevalence in green plants, their exact roles and formation mechanisms remain unclear. To explore these issues, we obtained Arabidopsis thaliana mutants with excess stromule formation in the leaf epidermis by microscopy-based screening. Here, we characterized one of these mutants, stromule biogenesis altered 1 (suba1). suba1 forms plastids with severely altered morphology in a variety of non-mesophyll tissues, such as leaf epidermis, hypocotyl epidermis, floral tissues, and pollen grains, but apparently normal leaf mesophyll chloroplasts. The suba1 mutation causes impaired chloroplast pigmentation and altered chloroplast ultrastructure in stomatal guard cells, as well as the aberrant accumulation of lipid droplets and their autophagic engulfment by the vacuole. The causal defective gene in suba1 is TRIGALACTOSYLDIACYLGLYCEROL5 (TGD5), which encodes a protein putatively involved in the endoplasmic reticulum (ER)-to-plastid lipid trafficking required for the ER pathway of thylakoid lipid assembly. These findings suggest that a non-mesophyll-specific mechanism maintains plastid morphology. The distinct mechanisms maintaining plastid morphology in mesophyll versus non-mesophyll plastids might be attributable, at least in part, to the differential contributions of the plastidial and ER pathways of lipid metabolism between mesophyll and non-mesophyll plastids.

  • Arabidopsis egy1 is critical for chloroplast development in leaf epidermal guard cells

    Sanjaya A.

    Plants ( Plants )  10 ( 6 )   2021.06 [ Peer Review Accepted ]

    Type of publication: Research paper (scientific journal)

     View Summary

    In Arabidopsis thaliana, the Ethylene-dependent Gravitropism-deficient and Yellow-green 1 (EGY1) gene encodes a thylakoid membrane-localized protease involved in chloroplast development in leaf mesophyll cells. Recently, EGY1 was also found to be crucial for the maintenance of grana in mesophyll chloroplasts. To further explore the function of EGY1 in leaf tissues, we examined the phenotype of chloroplasts in the leaf epidermal guard cells and pavement cells of two 40Ar17+ irradiation-derived mutants, Ar50-33-pg1 and egy1-4. Fluorescence microscopy revealed that fully expanded leaves of both egy1 mutants showed severe chlorophyll deficiency in both epidermal cell types. Guard cells in the egy1 mutant exhibited permanent defects in chloroplast formation during leaf expansion. Labeling of plastids with CaMV35S or Protodermal Factor1 (PDF1) promoter-driven stroma-targeted fluorescent proteins revealed that egy1 guard cells contained the normal number of plastids, but with moderately reduced size, compared with wild-type guard cells. Transmission electron microscopy further revealed that the development of thylakoids was impaired in the plastids of egy1 mutant guard mother cells, guard cells, and pavement cells. Collectively, these observations demonstrate that EGY1 is involved in chloroplast formation in the leaf epidermis and is particularly critical for chloroplast differentiation in guard cells.

  • Arabidopsis thaliana Leaf Epidermal Guard Cells: A Model for Studying Chloroplast Proliferation and Partitioning in Plants

    Fujiwara M.

    Frontiers in Plant Science ( Frontiers in Plant Science )  10   1403 - 1403   2019.10 [ Peer Review Accepted ]

    Type of publication: Research paper (scientific journal)

     View Summary

    The existence of numerous chloroplasts in photosynthetic cells is a general feature of plants. Chloroplast biogenesis and inheritance involve two distinct mechanisms: proliferation of chloroplasts by binary fission and partitioning of chloroplasts into daughter cells during cell division. The mechanism of chloroplast number coordination in a given cell type is a fundamental question. Stomatal guard cells (GCs) in the plant shoot epidermis generally contain several to tens of chloroplasts per cell. Thus far, chloroplast number at the stomatal (GC pair) level has generally been used as a convenient marker for identifying hybrid species or estimating the ploidy level of a given plant tissue. Here, we report that Arabidopsis thaliana leaf GCs represent a useful system for investigating the unexploited aspects of chloroplast number control in plant cells. In contrast to a general notion based on analyses of leaf mesophyll chloroplasts, a small difference was detected in the GC chloroplast number among three Arabidopsis ecotypes (Columbia, Landsberg erecta, and Wassilewskija). Fluorescence microscopy often detected dividing GC chloroplasts with the FtsZ1 ring not only at the early stage of leaf expansion but also at the late stage. Compensatory chloroplast expansion, a phenomenon well documented in leaf mesophyll cells of chloroplast division mutants and transgenic plants, could take place between paired GCs in wild-type leaves. Furthermore, modest chloroplast number per GC as well as symmetric division of guard mother cells for GC formation suggests that Arabidopsis GCs would facilitate the analysis of chloroplast partitioning, based on chloroplast counting at the individual cell level.

  • Arabidopsis PARC6 is critical for plastid morphogenesis in pavement, trichome, and guard cells in leaf epidermis

    Ishikawa H, Yasuzawa M, Koike N, Sanjaya A, Moriyama S, Nishizawa A, Matsuoka K, Sasaki S, Kazama Y, Hayashi Y, Abe T, Fujiwara MT, Itoh RD

    Frontiers in Plant Science ( Frontiers Media SA )  10   1665 - 1665   2019 [ Peer Review Accepted ]

    Type of publication: Research paper (scientific journal)

     View Summary

    Recently, a recessive Arabidopsis thaliana mutant with abundant stromules in leaf epidermal pavement cells was visually screened and isolated. The gene responsible for this mutant phenotype was identified as PARC6, a chloroplast division site regulator gene. The mutant allele parc6-5 carried two point mutations (G62R and W700stop) at the N- and C-terminal ends of the coding sequence, respectively. Here, we further characterized parc6-5 and other parc6 mutant alleles, and showed that PARC6 plays a critical role in plastid morphogenesis in all cell types of the leaf epidermis: pavement cells, trichome cells, and guard cells. Transient expression of PARC6 transit peptide (TP) fused to the green fluorescent protein (GFP) in plant cells showed that the G62R mutation has no or little effect on the TP activity of the PARC6 N-terminal region. Then, plastid morphology was microscopically analyzed in the leaf epidermis of wild-type (WT) and parc6 mutants (parc6-1, parc6-3, parc6-4 and parc6-5) with the aid of stroma-targeted fluorescent proteins. In parc6 pavement cells, plastids often assumed aberrant grape-like morphology, similar to those in severe plastid division mutants, atminE1, and arc6. In parc6 trichome cells, plastids exhibited extreme grape-like aggregations, without the production of giant plastids (>6 µm diameter), as a general phenotype. In parc6 guard cells, plastids exhibited a variety of abnormal phenotypes, including reduced number, enlarged size, and activated stromules, similar to those in atminE1 and arc6 guard cells. Nevertheless, unlike atminE1 and arc6, parc6 exhibited a low number of mini-chloroplasts (< 2 µm diameter) and rarely produced chloroplast-deficient guard cells. Importantly, unlike parc6, the chloroplast division site mutant arc11 exhibited WT-like plastid phenotypes in trichome and guard cells. Finally, observation of parc6 complementation lines expressing a functional PARC6-GFP protein indicated that PARC6-GFP formed a ring-like structure in both constricting and non-constricting chloroplasts, and that PARC6 dynamically changes its configuration during the process of chloroplast division.

  • Isolation and analysis of a stromule-overproducing Arabidopsis mutant suggest the role of PARC6 in plastid morphology maintenance in the leaf epidermis

    Itoh R.

    Physiologia Plantarum ( Physiologia Plantarum )  162 ( 4 ) 479 - 494   2018.04 [ Peer Review Accepted ]

    Type of publication: Research paper (scientific journal)

     View Summary

    Stromules, or stroma-filled tubules, are thin extensions of the plastid envelope membrane that are most frequently observed in undifferentiated or non-mesophyll cells. The formation of stromules is developmentally regulated and responsive to biotic and abiotic stress; however, the physiological roles and molecular mechanisms of the stromule formation remain enigmatic. Accordingly, we attempted to obtain Arabidopsis thaliana mutants with aberrant stromule biogenesis in the leaf epidermis. Here, we characterize one of the obtained mutants. Plastids in the leaf epidermis of this mutant were giant and pleomorphic, typically having one or more constrictions that indicated arrested plastid division, and usually possessed one or more extremely long stromules, which indicated the deregulation of stromule formation. Genetic mapping, whole-genome resequencing-aided exome analysis, and gene complementation identified PARC6/CDP1/ARC6H, which encodes a vascular plant-specific, chloroplast division site-positioning factor, as the causal gene for the stromule phenotype. Yeast two-hybrid assay and double mutant analysis also identified a possible interaction between PARC6 and MinD1, another known chloroplast division site-positioning factor, during the morphogenesis of leaf epidermal plastids. To the best of our knowledge, PARC6 is the only known A. thaliana chloroplast division factor whose mutations more extensively affect the morphology of plastids in non-mesophyll tissue than in mesophyll tissue. Therefore, the present study demonstrates that PARC6 plays a pivotal role in the morphology maintenance and stromule regulation of non-mesophyll plastids.

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Other Papers 【 display / non-display

  • Conservative and innovative systems of chloroplast division


    Rec Res Dev Plant Mol Biol ( その他の出版社 )  ( 1 ) 113 - 125   2003.03


Grant-in-Aid for Scientific Research 【 display / non-display

  • Grant-in-Aid for Scientific Research(C)

    Project Year: 2019.04  -  2023.03 

    Direct: 3,300,000 (YEN)  Overheads: 4,290,000 (YEN)  Total: 990,000 (YEN)

  • Grant-in-Aid for Scientific Research(C)

    Project Year: 2018.04  -  2022.03 

    Direct: 3,400,000 (YEN)  Overheads: 4,420,000 (YEN)  Total: 1,020,000 (YEN)

  • Regulation of stromule formation and its relation to plastid differentiation

    Grant-in-Aid for Scientific Research(C)

    Project Year: 2014.04  -  2017.03 

    Investigator(s): ITOH Ryuuichi, FUJIWARA Makoto 

    Direct: 3,900,000 (YEN)  Overheads: 5,070,000 (YEN)  Total: 1,170,000 (YEN)

     View Summary

    Generally, non-green plastids tend to possess highly developed stromule(s). In our previous study, the author obtained two mutants of Arabiodopsis in which overformation of stromules were observed in leaf epidermis. Using these mutants, the author studied the regulation of stromule formation and obtained some insights as follows: (i) SUBA1 is involved in the regulation of stromule formation globally over various tissues, (ii) SUBA2 might interact with MinD/E, (iii) suba mutations affect plastid morphology and/or movement in pollen grains and tubes.

  • Mechanism of FtsZ-independent plastid replication in plants

    Grant-in-Aid for Scientific Research(C)

    Project Year: 2013.04  -  2017.03 

    Investigator(s): FUJIWARA Makoto 

    Direct: 4,100,000 (YEN)  Overheads: 5,330,000 (YEN)  Total: 1,230,000 (YEN)

     View Summary

    We investigated the cellular mechanisms of plastid replication in the ftsZ-null mutant of Arabidopsis thaliana. Fluorescence microscopy analysis of both early- and late-developing ovule integuments indicated that ftsZ amyloplasts had no activity of division during the post-mitotic cell maturation, while ftsZ proplastids could be replicated during the cell proliferation stage, overcoming the defects of the plastid division apparatus.

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