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Dive into the research topics where Tamaki Uehara-Ichiki is active.

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Featured researches published by Tamaki Uehara-Ichiki.


PLOS Pathogens | 2012

Tubular Structure Induced by a Plant Virus Facilitates Viral Spread in Its Vector Insect

Qian Chen; Hongyan Chen; Qianzhuo Mao; Qifei Liu; Takumi Shimizu; Tamaki Uehara-Ichiki; Zujian Wu; Lianhui Xie; Toshihiro Omura; Taiyun Wei

Rice dwarf virus (RDV) replicates in and is transmitted by a leafhopper vector in a persistent-propagative manner. Previous cytopathologic and genetic data revealed that tubular structures, constructed by the nonstructural viral protein Pns10, contain viral particles and are directly involved in the intercellular spread of RDV among cultured leafhopper cells. Here, we demonstrated that RDV exploited these virus-containing tubules to move along actin-based microvilli of the epithelial cells and muscle fibers of visceral muscle tissues in the alimentary canal, facilitating the spread of virus in the body of its insect vector leafhoppers. In cultured leafhopper cells, the knockdown of Pns10 expression due to RNA interference (RNAi) induced by synthesized dsRNA from Pns10 gene strongly inhibited tubule formation and prevented the spread of virus among insect vector cells. RNAi induced after ingestion of dsRNA from Pns10 gene strongly inhibited formation of tubules, preventing intercellular spread and transmission of the virus by the leafhopper. All these results, for the first time, show that a persistent-propagative virus exploits virus-containing tubules composed of a nonstructural viral protein to traffic along actin-based cellular protrusions, facilitating the intercellular spread of the virus in the vector insect. The RNAi strategy and the insect vector cell culture provide useful tools to investigate the molecular mechanisms enabling efficient transmission of persistent-propagative plant viruses by vector insects.


Journal of Virology | 2009

Association of Rice Gall Dwarf Virus with Microtubules Is Necessary for Viral Release from Cultured Insect Vector Cells

Taiyun Wei; Tamaki Uehara-Ichiki; Naoyuki Miyazaki; Hiroyuki Hibino; Kenji Iwasaki; Toshihiro Omura

ABSTRACT Vector insect cells infected with Rice gall dwarf virus, a member of the family Reoviridae, contained the virus-associated microtubules adjacent to the viroplasms, as revealed by transmission electron, electron tomographic, and confocal microscopy. The viroplasms, putative sites of viral replication, contained the nonstructural viral proteins Pns7 and Pns12, as well as core protein P5, of the virus. Microtubule-depolymerizing drugs suppressed the association of viral particles with microtubules and prevented the release of viruses from cells without significantly affecting viral multiplication. Thus, microtubules appear to mediate viral transport within and release of viruses from infected vector cells.


Virus Research | 2011

Sequential infection of Rice dwarf virus in the internal organs of its insect vector after ingestion of virus

Hongyan Chen; Qian Chen; Toshihiro Omura; Tamaki Uehara-Ichiki; Taiyun Wei

Confocal microscopy revealed that Rice dwarf virus (RDV) initially accumulated in epithelial cells of the filter chamber of leafhopper vector Nephotettix cincticeps 2 days after acquisition access feeding on diseased plants. Subsequently, RDV accumulation progressed to the anterior midgut, and then spread to the nervous system before infection of other organs. Furthermore, RDV accumulation progressed to the visceral muscles surrounding the anterior midgut. Later, RDV accumulation was detected in other parts of the alimentary canal, salivary glands and the follicular cells of the ovarioles in viruliferous insect vector. Our results suggest that RDV may use the muscle or neural tissues for viral dissemination from the infected vectors midgut into other tissues.


Journal of Virological Methods | 2010

Molecular detection of nine rice viruses by a reverse-transcription loop-mediated isothermal amplification assay

Dung Tien Le; Osamu Netsu; Tamaki Uehara-Ichiki; Takumi Shimizu; Il-Ryong Choi; Toshihiro Omura; Takahide Sasaya

A reverse-transcription loop-mediated isothermal amplification (RT-LAMP) assay was established for the detection of nine viruses from infected rice plants, including rice black-streaked dwarf virus (RBSDV), rice dwarf virus (RDV), rice gall dwarf virus (RGDV), rice ragged stunt virus (RRSV), rice transitory yellowing virus (RTYV), rice stripe virus (RSV), rice grassy stunt virus (RGSV), rice tungro spherical virus (RTSV), and rice tungro bacilliform virus (RTBV). Virus-specific primer sets were designed from the genome sequences of these viruses. By the combination of RNA rapid extraction and RT-LAMP, these nine viruses could be detected within 2h from infected rice plants. The sensitivities of the assays were either higher than (for RSV, RTBV, and RTYV) or similar (for RDV) to those of one-step RT-PCR. Furthermore, RTBV and RTSV were detected not only in infected rice plants but also in viruliferous insect vectors. The RT-LAMP assays may facilitate studies on rice disease epidemiology, outbreak surveillance, and molecular pathology.


Journal of Virology | 2012

Crystallographic Analysis Reveals Octamerization of Viroplasm Matrix Protein P9-1 of Rice Black Streaked Dwarf Virus

Fusamichi Akita; Akifumi Higashiura; Takumi Shimizu; Yingying Pu; Mamoru Suzuki; Tamaki Uehara-Ichiki; Takahide Sasaya; Shuji Kanamaru; Fumio Arisaka; Tomitake Tsukihara; Atsushi Nakagawa; Toshihiro Omura

ABSTRACT The P9-1 protein of Rice black streaked dwarf virus accumulates in viroplasm inclusions, which are structures that appear to play an important role in viral morphogenesis and are commonly found in viruses in the family Reoviridae. Crystallographic analysis of P9-1 revealed structural features that allow the protein to form dimers via hydrophobic interactions. Each dimer has carboxy-terminal regions, resembling arms, that extend to neighboring dimers, thereby uniting sets of four dimers via lateral hydrophobic interactions, to yield cylindrical octamers. The importance of these regions for the formation of viroplasm-like inclusions was confirmed by the absence of such inclusions when P9-1 was expressed without its carboxy-terminal arm. The octamers are vertically elongated cylinders resembling the structures formed by NSP2 of rotavirus, even though there are no significant similarities between the respective primary and secondary structures of the two proteins. Our results suggest that an octameric structure with an internal pore might be important for the functioning of the respective proteins in the events that occur in the viroplasm, which might include viral morphogenesis.


Journal of Virology | 2008

Structural evolution of reoviridae revealed by oryzavirus in acquiring the second capsid shell.

Naoyuki Miyazaki; Tamaki Uehara-Ichiki; Li Xing; Leif Bergman; Akifumi Higashiura; Atsushi Nakagawa; Toshihiro Omura; R. Holland Cheng

ABSTRACT The conservation of the core structure and diversification of the external features among the turreted reoviruses appear to be relevant to structural evolution in facilitating the infection of diverse host species. The structure of Rice ragged stunt virus (RRSV), in the genus Oryzavirus of the family Reoviridae, is determined to show a core composed of capsid shell, clamps, and long turrets. The RRSV core structure is equivalent to the core structure of Orthoreovirus and the virion structure of Cytoplasmic polyhedrosis virus (CPV). In RRSV, five peripheral trimers surround each long turret and sit at the Q trimer position in the T=13l icosahedral symmetry, a structural feature unique to turreted reoviruses. That is, the core of RRSV is partially covered by 60 copies of the peripheral trimer. In contrast, the core of Orthoreovirus is covered by 200 copies of the trimer that sit at the Q, R, S, and T trimer positions. Our results suggest that among the three viruses, RRSV has a structure intermediate between that of Orthoreovirus and the CPV virion. This conclusion coincides with the results of the phylogenetic analysis of amino acid sequences of RNA-dependent RNA polymerases.


Virus Research | 2011

Immunity to Rice black streaked dwarf virus, a plant reovirus, can be achieved in rice plants by RNA silencing against the gene for the viroplasm component protein.

Takumi Shimizu; Eiko Nakazono-Nagaoka; Fusamichi Akita; Tamaki Uehara-Ichiki; Toshihiro Omura; Takahide Sasaya

The nonstructural protein P9-1 of Rice black streaked dwarf virus has been confirmed to accumulate in viroplasms, the putative sites of viral replication, in infected plants and insects. We transformed rice plants by introducing an RNA interference construct against the P9-1-encoding gene. The resultant transgenic plants accumulated short interfering RNAs specific to the construct. All progenies produced by self-fertilization of these transgenic plants with induced RNA interference against the gene for P9-1 were resistant to infection by the virus. Our results demonstrated that interfering with the expression of a viroplasm component protein of plant reoviruses, which plays an important role in viral proliferation, might be a practical and effective way to control plant reovirus infection in crop plants.


Journal of Virology | 2011

Rice Dwarf Viruses with Dysfunctional Genomes Generated in Plants Are Filtered Out in Vector Insects: Implications for the Origin of the Virus

Yingying Pu; Akira Kikuchi; Yusuke Moriyasu; Masatoshi Tomaru; Yan Jin; Haruhisa Suga; Kyoji Hagiwara; Fusamichi Akita; Takumi Shimizu; Osamu Netsu; Nobuhiro Suzuki; Tamaki Uehara-Ichiki; Takahide Sasaya; Taiyun Wei; Yi Li; Toshihiro Omura

ABSTRACT Rice dwarf virus (RDV), with 12 double-stranded RNA (dsRNA) genome segments (S1 to S12), replicates in and is transmitted by vector insects. The RDV-plant host-vector insect system allows us to examine the evolution, adaptation, and population genetics of a plant virus. We compared the effects of long-term maintenance of RDV on population structures in its two hosts. The maintenance of RDV in rice plants for several years resulted in gradual accumulation of nonsense mutations in S2 and S10, absence of expression of the encoded proteins, and complete loss of transmissibility. RDV maintained in cultured insect cells for 6 years retained an intact protein-encoding genome. Thus, the structural P2 protein encoded by S2 and the nonstructural Pns10 protein encoded by S10 of RDV are subject to different selective pressures in the two hosts, and mutations accumulating in the host plant are detrimental in vector insects. However, one round of propagation in insect cells or individuals purged the populations of RDV that had accumulated deleterious mutations in host plants, with exclusive survival of fully competent RDV. Our results suggest that during the course of evolution, an ancestral form of RDV, of insect virus origin, might have acquired the ability to replicate in a host plant, given its reproducible mutations in the host plant that abolish vector transmissibility and viability in nature.


Phytopathology | 2013

Strong resistance against Rice grassy stunt virus is induced in transgenic rice plants expressing double-stranded RNA of the viral genes for nucleocapsid or movement proteins as targets for RNA interference.

Takumi Shimizu; Takumi Ogamino; Akihiro Hiraguri; Eiko Nakazono-Nagaoka; Tamaki Uehara-Ichiki; Masami Nakajima; Katsumi Akutsu; Toshihiro Omura; Takahide Sasaya

Rice grassy stunt virus (RGSV), a member of the genus Tenuivirus, causes significant economic losses in rice production in South, Southeast, and East Asian countries. Growing resistant varieties is the most efficient method to control RGSV; however, suitable resistance genes have not yet been found in natural rice resources. One of the most promising methods to confer resistance against RGSV is the use of RNA interference (RNAi). It is important to target viral genes that play important roles in viral infection and proliferation at an early stage of viral replication. Our recent findings obtained from an RNAi experiment with Rice stripe virus (RSV), a tenuivirus, revealed that the genes for nucleocapsid and movement proteins were appropriate targets for RNAi to confer resistance against RSV. In this study, we transformed rice plants by introducing an RNAi construct of the RGSV genes for the nucelocapsid protein pC5 or movement protein pC6. All progenies from self-fertilized transgenic plants had strong resistance against RGSV infection and did not allow the proliferation of RGSV. Thus, our strategy to target genes for nucleocapsid and movement proteins for conferring viral resistance might be applicable to the plant viruses in the genus Tenuivirus.


Frontiers in Microbiology | 2014

Transgenic strategies to confer resistance against viruses in rice plants

Takahide Sasaya; Eiko Nakazono-Nagaoka; Hiroaki Saika; Hideyuki Aoki; Akihiro Hiraguri; Osamu Netsu; Tamaki Uehara-Ichiki; Masatoshi Onuki; Seichi Toki; Koji Saito; Osamu Yatou

Rice (Oryza sativa L.) is cultivated in more than 100 countries and supports nearly half of the world’s population. Developing efficient methods to control rice viruses is thus an urgent necessity because viruses cause serious losses in rice yield. Most rice viruses are transmitted by insect vectors, notably planthoppers and leafhoppers. Viruliferous insect vectors can disperse their viruses over relatively long distances, and eradication of the viruses is very difficult once they become widespread. Exploitation of natural genetic sources of resistance is one of the most effective approaches to protect crops from virus infection; however, only a few naturally occurring rice genes confer resistance against rice viruses. Many investigators are using genetic engineering of rice plants as a potential strategy to control viral diseases. Using viral genes to confer pathogen-derived resistance against crops is a well-established procedure, and the expression of various viral gene products has proved to be effective in preventing or reducing infection by various plant viruses since the 1990s. RNA interference (RNAi), also known as RNA silencing, is one of the most efficient methods to confer resistance against plant viruses on their respective crops. In this article, we review the recent progress, mainly conducted by our research group, in transgenic strategies to confer resistance against tenuiviruses and reoviruses in rice plants. Our findings also illustrate that not all RNAi constructs against viral RNAs are equally effective in preventing virus infection and that it is important to identify the viral “Achilles’ heel” gene to target for RNAi attack when engineering plants.

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Toshihiro Omura

Tokyo University of Agriculture and Technology

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Takahide Sasaya

National Agriculture and Food Research Organization

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Akihiro Hiraguri

Tokyo University of Agriculture and Technology

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Eiko Nakazono-Nagaoka

National Agriculture and Food Research Organization

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Taiyun Wei

Fujian Agriculture and Forestry University

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