• BMB Reports
• /
• v.41 no.5
• /
• pp.376-381
• /
• 2008

The discovery of RNA silencing inhibition by virus encoded suppressors or low temperature leads to concerns about the stability of transgenic resistance. RNA-dependent RNA polymerase (RdRp) has been previously characterized to be essential for transgene-mediated RNA silencing. Here we showed that low temperature led to the inhibition of RNA silencing, the loss of viral resistance and the reduced expression of host RdRp homolog (NtRdRP1) in transgenic T4 progeny with untranslatable potato virus Y coat protein (PVY-CP) gene. Moreover, RNA silencing and the associated resistance were differently inhibited by potato virus X (PVX) and tobacco mosaic virus (TMV) infections. The increased expression of NtRdRP1 in both PVX and TMV infected plants indicated its general role in response to viral pathogens. Collectively, we propose that biotic and abiotic stress factors affect RNA silencing-mediated resistance in transgenic tobacco plants and that their effects target different steps of RNA silencing.

• The Plant Pathology Journal
• /
• v.27 no.3
• /
• pp.197-206
• /
• 2011

RNA silencing has had a large impact on biology in general, as well as on our understanding of plant-pathogen interactions, especially interactions between plants and viruses. While most of what we know about the mechanism of RNA silencing was deduced in the last 12 years, many of the interactions between plants and viruses, as well as virus-virus interactions in plants, which we now know are manifestations of RNA silencing, were the subject of decades of work from numerous laboratories. These laboratories were examining the nature and extent of phenomena such as recovery from infection, the formation of dark green islands resistant to re-infection, synergy between unrelated viruses and cross-protection between related viruses, all first described in the late 1920s. In this review, the relationships between these phenomena and their place in the defense mechanism we call RNA silencing will be described, to show how they are all linked.

• Journal of Microbiology
• /
• v.34 no.1
• /
• pp.61-67
• /
• 1996

Double-stranded RNA (dsRNA) viruses and single-stranded RNA(ssRNA) viruses were detected in a strain of Pleurotus mushroom cultivated in a farm. Those fungal virsus were purified in the pH 6.0 or pH 7.2 using CsCI or Cs$_{2}$SO$_{4}$ buoyant density centrifugation. Each viral particles were not completely separated at any trials. However, mushroom bacili-form virus contains a single major nucleic acid with 0.7 Kb ssRNA, which might code for 20 Kd viral capsid protein. The dsRNAs are encapsidatred into spherical-form viruses, whereas ssRNA viral genomes are encapsidated into two different sizes of bacili-form particles. A healthy-looking mushroom also contained some spherical-form viruses with dsRNAs. Laboratory strains of Pleurotus ostreatus and a cultivated strain of P. sajor-caju did not show any viral particles. Mushrooms with specific disease symptoms. however, contained at least four different sizes of spherical-form viruses. Thus, we concluded that a bacilli-form virus case a severe disease symptoms of adnormal on mushroom development.

• Korean Journal of Plant Tissue Culture
• /
• v.24 no.3
• /
• pp.153-160
• /
• 1997

Cucumber mosaic virus (CMV) leads to a cause of poor crop productivity and quality. To solve this problem, we attempted to develop a virus-resistance tobacco plants by using viral coat protein (CP) gene. Transgenic tobacco plants expressing CMV CP gene were analysed by the resistance upon CMV infection. The virus-resistance was measured in $\textrm{T}_{1}$, generation by the inhibition of plant growth and the expression of the mosaic symptoms infected with CMV. The transgenic lines were divided into four groups: highly resistant, resistant, moderate and susceptible based on their growth and symptom severity. Out of 39 transgenic lines, 16 lines showed significant virus-resistance. And of resistant lines, 2 lines were designated highly resistant based on the facts that they achieved similar plant height to that of non-infected tobacco plants and showed lower disease symptom than that of other lines. The steady state level of CP RNA and coat protein level were measured by northern blot and immunoblot analysis. The CP RNA was highly accumulated in most resistant and moderate lines but barely detected in susceptible lines. The coat protein was detected in most lines regardless of their resistance to CMV. from this result, virus-resistance appeared to correlate more with CP RNA level than the level of coat protein. However, in two highly resistant lines, CP RNA level was unexpectedly low. This unexpected phenomenon need to be further investigated.

• The Plant Pathology Journal
• /
• v.21 no.4
• /
• pp.343-348
• /
• 2005

The partial nucleotide sequences of the genomic dsRNA mycoviruses infecting Pleurotus ostreatus (isolates ASI2596, ASI2597, and Bupyungbokhoe) and Agaricus blazei Murrill were determined and compared with those of the other dsRNA mycoviruses. Partial nucleotide sequences of the purified dsRNA from ASI2596 and ASI2597 revealed RNA-dependent RNA polymerase sequences that are closely related to Oyster mushroom isometric virus 2, while nucleotide sequences and the deduced amino acid sequence from dsRNA mycovirus infecting Agaricus blazei did not show any significant homology to the other dsRNA mycoviruses. Specific primers were designed for RT-PCR detection of these dsRNA viruses and were found to specifically detect each dsRNA virus. Northern blot analysis confirmed the homogeneity of RT-PCR products to each purified dsRNA. Altogether, our results suggest that these virus-specific primer sets can be employed for the specific detection of each dsRNA mycovirus in infected mushrooms.

• Proceedings of the Korean Society of Plant Pathology Conference
• /
• 2003.10a
• /
• pp.146.2-147
• /
• 2003

Two Korean isolates of Alfalfa mosaic virus (AHV-AZ, AMV-KR) were isolated from azuki bean and potato plants, respectively, and their pathologies were confirmed on some susceptible host plants including pepper, tobacco and red bean plants. Full length cDNAs to RNA1, RNA2 and RNA3 of the two Korean strains were amplified using the long-template reverse transcription (RT)-polymerase chain reaction (PCR) method. RT-PCR products covering entire regions for the three AMV genome RNAs were cloned. RNA transcripts were synthesized in vitro from each clones using T7 RNA polymerase and infectivity test was peformed in 9 reassortment sets of transcripts. All the combinations of reassorted transcripts were found to be infectious when inoculated onto Nicotiana benthamiana plants, and were not distinguishable to those of wild types. The full-length cDNA clones that were confirmed infectious were sequenced their nucleotide sequences. We will discuss sequence analysis of the two Korean isolates of AMV genomic RNA3 and compare reported foreign isolates of AMV.

• The Plant Pathology Journal
• /
• v.27 no.4
• /
• pp.315-323
• /
• 2011

Soybean plants infected with Bean pod mottle virus (BPMV) develop acute symptoms that usually decrease in severity over time. In other plant-virus interactions, this type of symptom recovery has been associated with degradation of viral RNAs by RNA silencing, which is accompanied by the accumulation of virus-derived small interfering RNAs (siRNAs). In this study, changes in the accumulation of BPMV siRNAs were investigated in soybean plants infected with BPMV alone, or infected with both BPMV and Soybean mosaic virus (SMV) and in transgenic soybean plants expressing SMV helper component-protease (HC-Pro). In many potyviruses, HC-Pro is a potent suppressor of RNA silencing. In plants infected with BPMV alone, accumulation of siRNAs was positively correlated with symptom severity and accumulation of BPMV genomic RNAs. Plants infected with both BPMV and SMV and BPMV-infected transgenic soybean plants expressing SMV HC-Pro exhibited severe symptoms characteristic of BPMVSMV synergism, and showed enhanced accumulation of BPMV RNAs and siRNAs compared to plants infected with BPMV alone and nontransgenic plants. Likewise, SMV HC-Pro enhanced the accumulation of siRNAs produced from a silenced green fluorescent protein gene in transient expression assays, while the P19 silencing suppressor of Tomato bushy stunt virus did not. Consistent with the modes of action of HC-Pro in other systems, which have shown that HC-Pro suppresses RNA silencing by preventing the unwinding of duplex siRNAs and inhibiting siRNA methylation, these studies showed that SMV HC-Pro interfered with the activities of RNA-induced silencing complexes, but not the activities of Dicer-like enzymes in antiviral defenses.

• Korean Journal of Microbiology
• /
• v.33 no.2
• /
• pp.105-110
• /
• 1997

Ustilago maydis strains (A-series and SH-series) containg virus or viral dsRNAs were artificially mated in corn seedling to generate 6 progeny strains, designated A23, A45, A21l, A31O, SH24 and SH61O. The dsRNA patterns of progeny strains were identical to those of the parental strains and there was no molecular exclusion mechanism among dsRNAs of parental strains. Virus particles were purified from 6 progeny strains and viral dsRNAs were analyzed on 5% PAGE. There was no mixed encapsidation between virus or dsRNAs of parental strains. Progeny strain SH6l4 produced toxin which inhibits the growth of SH9, SHIO and SH11. Likewise, toxins from A310 and SH24 inhibited growth of the SH11 strains. These results indicate that the presence of different types of dsRNA does not interfere the expression of toxin gene.

• The Journal of Korean Society of Virology
• /
• v.27 no.1
• /
• pp.1-8
• /
• 1997

Human caliciviruses (HuCVs) cause sporadic cases and outbreaks of acute gastroenteritis (AGE). Three major genogroups of HuCVs have been described including the Norwalk virus (NV)-, the Snow Mountain virus (SMA)-, and the Sapporo-genogroups. This study describes the detection and genetic variation of HuCVs from hospitalized infants with AGE in Korea by RT-PCR and sequencing. The cDNA fragments of 206 to 470bp corresponding to the region of 3 primer pairs (36/35, 35/51 or 3/51) in the polymerase region of NV were generated. Of 185 stools screened, 8% were positive by RT-PCR and their sequences showed that all strains contained the GLPSG and YGDD motifs which are conserved for HuCVs. Amino acid (aa) sequence analysis showed that these strains can be divided into 3 major genogroups. High conservation was observed in that one strain shares 100% of aa sequence with Southampton virus, another shares 99% with the Sapporo virus, and six strains share 90 to 95% with Snow Mountain virus. However, significant sequence variation was also found in other strains. This study indicates that all major genogroups of HuCVs are circulating in Korea.

• The Plant Pathology Journal
• /
• v.15 no.2
• /
• pp.119-123
• /
• 1999

Chrysanthemums showing leaf mottling were collected from three southern locations in Korea in 1998. Two kinds of viruses were isolated from the leaves and were identified as tomato aspermy virus ch-TAV) and chrysanthemum virus B (ch-CVB), according to their host range, morphology, intracellular location, agar gel double diffusion test, and double-stranded RNA (dsRNA) analysis. The purified ch-TAV was spherical particles of approximately 29 nm in diameter and ch-CVB was filamentous particles of 685 nm long. Inclusion bodies were not observed in ch-TAV and/or ch-CVB infected chrysanthemum. ch-TAV showed positive serological reaction with TAV antiserum (ATCC-127) but not with CMV-pepper antiserum. In dsRNA analysis, four kinds of viral dsRNA were observed on ch-TAV and one viral dsRNA was shown on ch-CVB. Rate of co-infection with TAV and CVB in commercial chrysanthemums was 20.9%. On the other hand, infection with CVB alone was 97.2%. However, chrysanthemums naturally infected with TAV alone were not found.