Engineering of stable infectious cDNA constructs of a fluorescently tagged tomato chlorosis virus

Tomato chlorosis virus (ToCV) is an emerging pathogen that cause severe yellow leaf disorder syndrome in tomato plants. In this study, we aimed to generate a recombinant ToCV tagged with green fluorescent protein (GFP) to enable real-time monitoring of viral infection in living plants. Transformation of the full-length cDNA construct of ToCV RNA1 into Escherichia coli resulted in instability issues, which were successfully overcome by inserting a plant intron into RNA1. Subsequently, a GFP tag was engineered into a cDNA construct of ToCV RNA2. The resulting recombinant ToCV-GFP could systemically infect Nicotiana benthamiana plants, and GFP expression was observed along the major veins. Utilizing ToCV-GFP, we also showed that ToCV engages in antagonistic relationships with two different tomato-infecting viruses in mixed infections in N. benthamiana. This study demonstrates the potential of ToCV-GFP as a valuable tool for the visual tracking of infection and movement of criniviruses in living plants.

The VP53 protein encoded by RNA2 of a fabavirus, broad bean wilt virus 2, is essential for viral systemic infection

Plant viruses evolves diverse strategies to overcome the limitations of their genomic capacity and express multiple proteins, despite the constraints imposed by the host translation system. Broad bean wilt virus 2 (BBWV2) is a widespread viral pathogen, causing severe damage to economically important crops. It is hypothesized that BBWV2 RNA2 possesses two alternative in-frame translation initiation codons, resulting in the production of two largely overlapping proteins, VP53 and VP37. In this study, we aim to investigate the expression and function of VP53, an N-terminally 128-amino-acid-extended form of the viral movement protein VP37, during BBWV2 infection. By engineering various recombinant and mutant constructs of BBWV2 RNA2, here we demonstrate that VP53 is indeed expressed during BBWV2 infection. We also provide evidence of the translation of the two overlapping proteins through ribosomal leaky scanning. Furthermore, our study highlights the indispensability of VP53 for successful systemic infection of BBWV2, as its removal results in the loss of virus infectivity. These insights into the translation mechanism and functional role of VP53 during BBWV2 infection significantly contribute to our understanding of the infection mechanisms employed by fabaviruses.

Effects of nurse managers' inclusive leadership on nurses' psychological safety and innovative work behavior: The moderating role of collectivism

INTRODUCTION

In the rapidly evolving healthcare landscape, the capacity to foster innovative work behavior among nurses is increasingly important. This study examined the dynamics between inclusive leadership, psychological safety, collectivism, and innovative work behavior among nurses.

DESIGN

The study used a cross-sectional, correlational design.

METHODS

This study utilized data from 730 medical-surgical nurses who provided direct care to patients. Standardized instruments were used to assess key study variables. Statistical analyses, including moderated mediation regressions, were employed to investigate the complex interplay among these variables.

RESULTS

We found a positive association between inclusive leadership and innovative work behavior, and psychological safety mediated this relationship. Collectivism moderated inclusive leadership's direct relationship with psychological safety and its indirect relationship with innovative work behavior. The results revealed that nurses with lower levels of collectivism were more responsive to their managers' inclusive behaviors, strengthening the relation between inclusive leadership, psychological safety, and innovative work behavior.

CONCLUSION

Our findings suggest that promoting inclusive leadership behaviors among nurse managers to create a psychologically safe environment can motivate nurses to engage in innovative work behavior. However, it is also important to understand that the effectiveness of leadership may differ depending on the collectivist values of individual nurses.

CLINICAL RELEVANCE

Nurse managers should adopt inclusive leadership behaviors, such as valuing trust, open communication, and diversity, in order to foster psychological safety and innovative work behavior among nurses.

Visual tracking of viral infection dynamics reveals the synergistic interactions between cucumber mosaic virus and broad bean wilt virus 2

Cucumber mosaic virus (CMV) is one of the most prevalent plant viruses in the world, and causes severe damage to various crops. CMV has been studied as a model RNA virus to better understand viral replication, gene functions, evolution, virion structure, and pathogenicity. However, CMV infection and movement dynamics remain unexplored due to the lack of a stable recombinant virus tagged with a reporter gene. In this study, we generated a CMV infectious cDNA construct tagged with a variant of the flavin-binding LOV photoreceptor (iLOV). The iLOV gene was stably maintained in the CMV genome after more than four weeks of three serial passages between plants. Using the iLOV-tagged recombinant CMV, we visualized CMV infection and movement dynamics in living plants in a time course manner. We also examined whether CMV infection dynamics is influenced by co-infection with broad bean wilt virus 2 (BBWV2). Our results revealed that no spatial interference occurred between CMV and BBWV2. Specifically, BBWV2 facilitated the cell-to-cell movement of CMV in the upper young leaves. In addition, the BBWV2 accumulation level increased after co-infection with CMV.

First report of citrus leaf blotch virus infecting Viburnum lentago in South Korea

Viburnum lentago (family Adoxaceae) is a perennial plant species native to northeastern United States and southern Canada. Globally, V. lentago is a popular garden plant due to its abundant flowers and beautiful autumnal color. V. lentago is also commercially cultivated for medicinal purposes because its roots and fruits can be used in herbal preparations (Jiao et al. 2021). In June 2022, virus-like symptoms of vein chlorosis and yellowing were observed in the leaves of many V. lentago trees planted in a public park in Wonju, South Korea. Leaf samples were collected from five symptomatic V. lentago trees. To identify the causal agent(s) of the virus-like symptoms, total RNA was isolated from one sample using PureLink® RNA Mini Kit (Invitrogen, USA) and subjected to library construction using Illumina TruSeq RNA Sample Preparation Kit v2 (Illumina, Inc., USA). RNA-Seq was performed using an Illumina NovaSeq 6000 system (Macrogen, Korea). De novo assembly of 118,878,556 quality-filtered reads was performed using the Trinity pipeline (Kwon et al. 2018), yielding 296,109 contigs. BLASTn and BLASTx analyses of the contigs against the GenBank viral reference database identified only one large contig (8,816 nt) containing a 26-nt poly(A) tail of viral origin. This contig had a maximum nucleotide identity of 85.53 % (with 99 % coverage) with isolate HZ (accession No. MH427034) of citrus leaf blotch virus (CLBV; genus Citrivirus, family Betaflexiviridae), suggesting that the collected sample was infected with CLBV. All collected V. lentago samples were tested using RT-PCR with CLBV-specific primers (CLBV-Det-Fw 5'-AACGAGGCCAATTCTGCTAT-3' and CLBV-Det-Rv 5'-GACTGCTTGACTAACAC-CCA-3'). All samples were positive for CLBV. For biological indexing, sap from the symptomatic V. lentago leaves was mechanically inoculated to indicator plants, including Nicotiana benthamiana, N. occidentalis, N. tabacum, Datura stramonium, Chenopodium quinoa, Vigna unguiculata, and V. lentago. Three months later, only V. lentago developed the same vein chlorosis symptoms observed in the collected samples, and no other tested plants exhibited obvious symptoms. Further, only V. lentago sample tested positive for CLBV using RT-PCR analysis. To determine the complete genome sequence of the CLBV V. lentago isolate, the contig sequence was confirmed by de novo sequencing of the RT-PCR products amplified using CLBV-specific primers. The 5' terminal sequence of the contig was determined using the 5' rapid amplification of cDNA ends method (Seo et al. 2015). The full-length sequence of CLBV isolated from V. lentago was 8,795 nt in length (excluding poly(A) tail), and deposited in GenBank under the accession number OP751940. Although numerous isolates of CLBV have been identified in various plant species, including citrus, kiwi, and lemon plants (Cao et al. 2017), the V. lentago isolate is likely a distinct variant because its CP gene has a maximum nucleotide identity of 85.53 % with that of a kiwi isolate (MH339916). With little information available on viral diseases infecting V. lentago, this is the first identified and completely sequenced CLBV infecting V. lentago. Significantly, V. lentago plants infected with CLBV did not flower throughout the summer period, reducing their value as an ornamental plant. Furthermore, V. lentago might have acted as an intermediate host to transfer CLBV to other crops such as citrus. To the best of our knowledge, this is the first report of CLBV infecting V. lentago in South Korea and the world.

Effect of early hysterectomy on a risk of incident cardiovascular disease in women: a nationwide population-based cohort study

Aim

Women who inevitably underwent surgical hysterectomy before natural menopause may have an earlier increase in hematocrit and storage iron than women who continue menstruation, thereby increasing the risk of cardiovascular disease (CVD) early. We aimed to evaluate the association of women with hysterectomy vs. without hysterectomy before their 50s with the risk of incident CVD.

Methods

This was a retrospective-cohort study, 135,575 women aged 40 to 50 years in 2011–2014 were extracted from the Korean Health Insurance Review and Assessment Service data and after propensity score matching, 55,539 pairs were included in hysterectomy and non-hysterectomy group respectively. The primary endpoint was major adverse cardiac and cerebrovascular events (MACCE), a composite of cardiovascular death, myocardial infarction (MI), stroke, and coronary artery revascularization.

Results

After adjustment for confounding factors, hysterectomy group had an increased risk of MACCE compared with non-hysterectomy group (hazard ratio [HR], 1.25; 95% confidence interval [CI], 1.09–1.44). Regarding individual outcomes, cardiovascular death, MI, and coronary revascularization were comparable between the groups, whereas, the risk of stroke was significantly higher in hysterectomy group than non-hysterectomy group (HR, 1.31; 95% CI, 1.12–1.53). Even after excluding women who underwent oophorectomy, hysterectomy group had a higher risk of MACCE than non-hysterectomy group (HR, 1.24; 95% CI 1.06–1.44).

Conclusions

Early surgical menopause due to hysterectomy, not hormonal menopause, was associated with an increased risk for a composite of CVD, especially stroke. This suggest that the role of “uterus” as well as sex hormones may be important for the sharp increase in the risk of CVD in women after menopause.

Funding Acknowledgement

Type of funding sources: None.

Optimal strategy for antiplatelet therapy after endovascular revascularization in patients with lower extremity artery disease

Background

The duration of antiplatelet therapy after endovascular revascularization in patients with lower extremity artery disease (LEAD) has not been well established. This study aimed to evaluate the clinical outcome according to the duration of dual antiplatelet therapy (DAPT) in real practice.

Methods

From April 2009 to June 2019, 376 patients with LEAD underwent successful endovascular revascularization. After the procedure, the received single antiplatelet therapy (SAPT) or DAPT of various durations were classified into two groups (SAPT or DAPT <6 months vs. DAPT ≥6 months). The primary outcomes were major adverse cardiovascular events (MACEs) and major adverse limb events (MALEs). The safety outcome was moderate-to-severe bleeding according to the Global Use of Strategies to Open Occluded Arteries (GUSTO) criteria.

Results

Over the 40-month follow-up period, MACE occurred less frequently in the DAPT ≥6 months group than that in the SAPT or DAPT <6 months group (12.4% vs. 23.8%; hazard ratio [HR]: 0.56; 95% confidence interval [CI]: 0.35–0.89; p=0.014) after inverse probability-weighted adjustment and propensity-score matching analysis (HR: 0.55, 95% CI; 0.30–0.99, p=0.048). The incidence of MALE did not show significant difference between the two groups (DAPT ≥6 months group: 17.1% vs. SAPT or DAPT <6 months group: 13.1%; HR: 1.05; 95% CI: 0.62–1.78; p=0.846). A significant difference between the DAPT ≥6 months group and the SAPT or DAPT <6 months group was not observed regarding the incidence of moderate-to-severe GUSTO bleeding.

Conclusions

In patients with LEAD, DAPT for ≥6 months after endovascular revascularization was associated with a lower incidence of MACE.

Funding Acknowledgement

Type of funding sources: Public Institution(s). Main funding source(s): National Research Foundation of Korea (NRF) grant funded by the government of Korea (MSIT) (No. 2019R1G1A1100442).

The impact of statin treatment intensity after endovascular revascularization for lower extremity peripheral artery disease

Purpose

There are few Asian studies on the clinical impact of statin intensity on clinical outcomes in patients with peripheral artery disease (PAD). This study investigated the clinical impact of statin intensity in patients with PAD after endovascular revascularization.

Material and methods

From April 2009 to June 2019, 376 patients with lower extremity PAD treated with endovascular revascularization were enrolled. They were classified into three groups according to statin intensity: no-statin, low-to-moderate intensity (LMI), and high-intensity (HI) groups. The primary outcomes were major adverse cardiovascular events (MACE) and major adverse limb events (MALE).

Results

During the 40-month follow-up, MACE occurred less in the HI and LMI groups than the no-statin group (11.4% vs. 16.0% vs. 39%, p<0.001). In the adjusted Cox models, the HI group had the lowest MACE (hazard ratio [HR]: 0.347; 95% confidence interval [CI] 0.144–0.834; p=0.018) and MALE (HR: 0.344; 95% CI 0.120–0.989, p=0.048), while the LMI group had fewer MACE (HR: 0.319; 95% CI 0.169–0.604, p=0.048) than the no-statin group. HI therapy was associated with better outcomes in terms of MALE (HR: 0.377; 95% CI: 0.208–0.684; p=0.001) and repeat revascularization (HR: 0.449; 95% CI: 0.243–0.830; p=0.011) than the LMI group after the inverse probability treatment weighting analysis.

Conclusions

HI and LMI statin use is associated with a significant reduction of MACE than no statin use. Regarding MALE, HI statin use was associated with better outcomes than no statin or LMI statin use.

Funding Acknowledgement

Type of funding sources: Public Institution(s). Main funding source(s): National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (No. 2019R1G1A1100442).

A multiplex RT-PCR assay for detection of emergent pepper Tsw resistance-breaking variants of tomato spotted wilt virus in South Korea

Tomato spotted wilt virus (TSWV) is a highly destructive virus for pepper. Introgression of the resistance gene Tsw in pepper is used to manage TSWV worldwide; however, the occurrence of Tsw resistance-breaking (RB) variants threatens the pepper industry. Here, we developed a multiplex reverse-transcription PCR assay for detection of recently emerged Tsw RB variants in South Korea with high specificity and sensitivity.

Ethylene emitted by viral pathogen-infected pepper (Capsicum annuum L.) plants is a volatile chemical cue that attracts aphid vectors

Plant viruses are obligate intracellular pathogens, and most depend on insect vectors for transmission between plants. Viral infection causes various physiological and metabolic changes in host traits, which subsequently influence the behavior and fitness of the insect vectors. Cucumber mosaic virus (CMV), one of the most widespread pathogens in pepper (Capsicum annuum L.), is transmitted by aphid vectors in a non-persistent manner. Here, we examined whether CMV infection in pepper affects the behavior of aphid vectors (Myzus persicae and Aphis glycines) in pepper. Aphid preference test revealed that significantly more aphids were attracted to CMV-infected pepper plants than to healthy plants. Comparative transcriptome analysis revealed a significant activation of the ethylene biosynthesis pathway in CMV-infected pepper plants. Indeed, gas chromatography analysis demonstrated that ethylene emission was significantly increased by CMV infection in pepper plants. Elevated ethylene emission in ethephon-treated healthy pepper increased their attractiveness to aphids. In contrast, aphid preference decreased after chemical inhibition of ethylene biosynthesis in CMV-infected pepper plants. Our results suggest that the ethylene emitted by CMV infection is a volatile cue that regulates the attractiveness of pepper plants to M. persicae and A. glycines.

SlHair2 Regulates the Initiation and Elongation of Type I Trichomes on Tomato Leaves and Stems

Trichomes are hair-like structures that are essential for abiotic and biotic stress responses. Tomato Hair (H), encoding a C2H2 zinc finger protein, was found to regulate the multicellular trichomes on stems. Here, we characterized Solyc10g078990 (hereafter Hair2, H2), its closest homolog, to examine whether it was involved in trichome development. The H2 gene was highly expressed in the leaves, and its protein contained a single C2H2 domain and was localized to the nucleus. The number and length of type I trichomes on the leaves and stems of knock-out h2 plants were reduced when compared to the wild-type, while overexpression increased their number and length. An auto-activation test with various truncated forms of H2 using yeast two-hybrid (Y2H) suggested that H2 acts as a transcriptional regulator or co-activator and that its N-terminal region is important for auto-activation. Y2H and pull-down analyses showed that H2 interacts with Woolly (Wo), which regulates the development of type I trichomes in tomato. Luciferase complementation imaging assays confirmed that they had direct interactions, implying that H2 and Wo function together to regulate the development of trichomes. These results suggest that H2 has a role in the initiation and elongation of type I trichomes in tomato.

A one-step reverse-transcription loop-mediated isothermal amplification assay optimized for the direct detection of cucumber green mottle mosaic virus in cucurbit seeds

Cucumber green mottle mosaic virus (CGMMV) is a seed-borne virus that causes significant economic losses in farms cultivating cucurbit plants. With the increase in global trade of cucurbit seeds, it is essential to develop a rapid, reliable, and convenient diagnostic method for the direct detection of CGMMV in these seeds for prevention and management of the disease. Here, we developed a one-step reverse-transcription loop-mediated isothermal amplification (RT-LAMP) assay for the direct detection of CGMMV in cucurbit seeds. To improve the efficiency of the one-step RT-LAMP assay, six primers were designed to target the most conserved regions of the gene encoding the movement protein of CGMMV. Our one-step RT-LAMP assay was optimized to improve specificity and sensitivity for CGMMV detection in individual seeds. A comparison of the detection sensitivity revealed that our one-step RT-LAMP assay was 100-fold more sensitive than the current reverse transcription-polymerase chain reaction assay used for CGMMV quarantine in Korea. Collectively, the one-step RT-LAMP assay developed in the present study is appropriate for the direct detection of CGMMV in individual cucurbit seeds.

Resistance-Breaking Tomato Spotted Wilt Virus Variant that Recently Occurred in Pepper in South Korea is a Genetic Reassortant

Tomato spotted wilt virus (TSWV) is a destructive viral pathogen in various crops, including pepper. Although the single dominant gene Tsw has been utilized in pepper breeding to confer resistance to TSWV, the occurrence of TSWV variants that overcome Tsw-mediated resistance has been reported in various countries after several years of growing resistant cultivars. In this study, we determined the complete genome sequence of a resistance-breaking TSWV variant (TSWV-YI) that recently emerged in pepper in South Korea. TSWV-YI infected all of the resistant pepper cultivars tested. The phylogenetic and recombination analyses of the complete TSWV-YI genome sequence showed that it is a reassortant that acquired its L and M RNA segments from the existing South Korean TSWV population and its S RNA in an isolate from another country. Given that TSWV-YI is a resistance-breaking variant, it appears that reassortment of the S RNA led to the emergence of this variant that breaks the Tsw gene in pepper grown in South Korea. Our results suggest that resistance-breaking TSWV variants are a potential threat to pepper production in South Korea and that strategies to manage these variants should be developed to ensure sustainable pepper production.

Genetic plasticity in RNA2 is associated with pathogenic diversification of broad bean wilt virus 2

Broad bean wilt virus 2 (BBWV2) is an evolutionarily successful RNA virus with an extensive host range and worldwide distribution that causes severe damage to crops. While numerous BBWV2 isolates from various plant species have been identified and their genome sequences determined, little information is available on the virulence and symptomatic characteristics corresponding to the genomic sequences. In this study, we provide integrated information on the molecular and pathogenic characteristics of three genetically distant BBWV2 isolates: BBWV2-PC, -LS2, and P3 obtained from Gentiana scabra, Leonurus sibiricus, and Pisum sativum, respectively. Phylogenetic and diversity analyses of the BBWV2 population included 42 isolates from various host species and revealed that RNA2 has higher genetic plasticity than RNA1 and may have evolved under host-imposed constraints. In addition, we generated an infectious cDNA clone of BBWV2-PC RNA2 (pBBWV2-PC-R2). Pseudo-recombination analysis of pBBWV2-PC-R2 further demonstrated that RNA2 determines the pathogenic characteristics of the PC isolate.

Viral Strain-Specific Activation of Pathogen-Associated Molecular Pattern-Triggered Immunity Enhances Symptom Severity in Broad Bean Wilt Virus 2 Infection

Broad bean wilt virus 2 (BBWV2) is an emerging virus in various economically important crops, especially pepper (Capsicum annuum L.), worldwide. Recently, the emergence of various BBWV2 strains that induce severe symptoms has increased damage to pepper crops. While the symptomatic variations among virus strains should be associated with differences in the transcriptomic reprogramming of host plants upon infection, underlying molecular mechanisms and associated genes are largely unknown. In the present study, we employed transcriptome analysis to identify responsible host factors for symptom enhancement in the BBWV2-pepper pathosystem using two distinct BBWV2 strains, PAP1 (a severe strain) and RP1 (a mild strain). Comparative analysis of the differentially expressed genes (DEGs) revealed that various genes associated with pathogen-associated molecular pattern (PAMP)-triggered immunity (PTI) and ethylene signaling were significantly upregulated upon infection with the severe PAP1 strain, but not with the mild RP1 strain. Indeed, hormone analysis revealed that ethylene emission was significantly increased in pepper plants infected with PAP1. These observations imply that the activation of the PTI-associated defense responses reinforce symptom formation during BBWV2 infection in a virus strain-specific manner.

Newly emerged resistance-breaking variants of cucumber mosaic virus represent ongoing host-interactive evolution of an RNA virus

Understanding the evolutionary history of a virus and the mechanisms influencing the direction of its evolution is essential for the development of more durable strategies to control the virus in crop fields. While the deployment of host resistance in crops is the most efficient means to control various viruses, host resistance itself can act as strong selective pressure and thus play a critical role in the evolution of virus virulence. Cucumber mosaic virus (CMV), a plant RNA virus with high evolutionary capacity, has caused endemic disease in various crops worldwide, including pepper (Capsicum annuum L.), because of frequent emergence of resistance-breaking variants. In this study, we examined the molecular and evolutionary characteristics of recently emerged, resistance-breaking CMV variants infecting pepper. Our population genetics analysis revealed that the high divergence capacity of CMV RNA1 might have played an essential role in the host-interactive evolution of CMV and in shaping the CMV population structure in pepper. We also demonstrated that nonsynonymous mutations in RNA1 encoding the 1a protein enabled CMV to overcome the deployed resistance in pepper. Our findings suggest that resistance-driven selective pressures on RNA1 might have contributed in shaping the unique evolutionary pattern of CMV in pepper. Therefore, deployment of a single resistance gene may reduce resistance durability against CMV and more integrated approaches are warranted for successful control of CMV in pepper.

A Plant Virus-Based Vector System for Gene Function Studies in Pepper

While pepper (Capsicum annuum) is a highly recalcitrant species for genetic transformation studies, plant virus-based vectors can provide alternative and powerful tools for transient regulation and functional analysis of genes of interest in pepper. In this study, we established an effective virus-based vector system applicable for transient gain- and loss-of-function studies in pepper using Broad bean wilt virus2 (BBWV2). We engineered BBWV2 as a dual gene expression vector for simultaneous expression of two recombinant proteins in pepper cells. In addition, we established enhanced and stable expression of recombinant proteins from the BBWV2-based dual vector via coexpression of a heterologous viral suppressor of RNA silencing. We also developed a BBWV2-based virus-induced gene silencing (VIGS) vector, and we successfully silenced the phytoene desaturase gene (PDS) using the BBWV2-based VIGS vector in various pepper cultivars. Additionally, we optimized the BBWV2-based VIGS system in pepper by testing the efficiency of PDS gene silencing under different conditions. This BBWV2-based vector system represents a convenient approach for rapid and simple analysis of gene functions in pepper.

Complete Genome Sequences and Evolutionary Analysis of Cucurbit aphid-borne yellows virus Isolates from Melon in Korea

Complete genome sequences of 22 isolates of Cucurbit aphid-borne yellows virus (CABYV), collected from melon plants showing yellowing symptom in Korea during the years 2013-2014, were determined and compared with previously reported CABYV genome sequences. The complete genomes were found to be 5,680-5,684 nucleotides in length and to encode six open reading frames (ORFs) that are separated into two regions by a non-coding internal region (IR) of 199 nucleotides. Their genomic organization is typical of the genus Polerovirus. Based on phylogenetic analyses of complete nucleotide (nt) sequences, CABYV isolates were divided into four groups: Asian, Mediterranean, Taiwanese, and R groups. The Korean CABYV isolates clustered with the Asian group with > 94% nt sequence identity. In contrast, the Korean CABYV isolates shared 87-89% sequence identities with the Mediterranean group, 88% with the Taiwanese group, 81-84% with the CABYV-R group, and 72% with another polerovirus, M.. Recombination analyses identified 24 recombination events (12 different recombination types) in the analyzed CABYV population. In the Korean CABYV isolates, four recombination types were detected from eight isolates. Two recombination types were detected in the IR and P3-P5 regions, respectively, which have been reported as hotspots for recombination of CABYV. This result suggests that recombination is an important evolutionary force in the genetic diversification of CABYV populations.

Elements Involved in the Rsv3-Mediated Extreme Resistance against an Avirulent Strain of Soybean Mosaic Virus

Extreme resistance (ER) is a type of R-gene-mediated resistance that rapidly induces a symptomless resistance phenotype, which is different from the phenotypical R-resistance manifested by the programmed cell death, accumulation of reactive oxygen species, and hypersensitive response. The Rsv3 gene in soybean cultivar L29 is responsible for ER against the avirulent strain G5H of soybean mosaic virus (SMV), but is ineffective against the virulent strain G7H. Rsv3-mediated ER is achieved through the rapid accumulation of callose, which arrests SMV-G5H at the point of infection. Callose accumulation, however, may not be the lone mechanism of this ER. Analyses of RNA-seq data obtained from infected soybean plants revealed a rapid induction of the abscisic acid pathway at 8 h post infection (hpi) in response to G5H but not to G7H, which resulted in the down-regulation of transcripts encoding β-1,3 glucanases that degrade callose in G5H-infected but not G7H-infected plants. In addition, parts of the autophagy and the small interfering (si) RNA pathways were temporally up-regulated at 24 hpi in response to G5H but not in response to G7H. The jasmonic acid (JA) pathway and many WRKY factors were clearly up-regulated only in G7H-infected plants. These results suggest that ER against SMV-G5H is achieved through the quick and temporary induction of ABA, autophagy, and the siRNA pathways, which rapidly eliminate G5H. The results also suggest that suppression of the JA pathway in the case of G5H is important for the Rsv3-mediated ER.

Complete Genome Sequence Analysis of Two Divergent Groups of Sweet potato chlorotic fleck virus Isolates Collected from Korea

The Sweet potato chlorotic fleck virus (SPCFV), of the genus Carlavirus (family Betaflexiviridae), was first detected as one of several viruses infecting sweet potatoes (Ipomea batatas L.) in Korea. Out of 154 sweet potato samples collected in 2012 that were showing virus-like symptoms, 47 (31%) were infected with SPCFV, along with other viruses. The complete genome sequences of four SPCFV isolates were determined and analyzed using previously reported genome sequences. The complete genomes were found to contain 9,104-9,108 nucleotides, excluding the poly-A tail, containing six putative open reading frames (ORFs). Further, the SPCFV Korean isolates were divided into two groups (Group I and Group II) by phylogenetic analysis based on the complete nucleotide sequences; Group I and Group II had low nucleotide sequence identities of about 73%. For the first time, we determined the complete genome sequence for the Group II SPCFV isolates. The amino acid sequence identity in coat proteins (CP) between the two groups was over 90%, whereas the amino acid sequence identity in other proteins was less than 80%. In addition, SPCFV Korean isolates had a low amino acid sequence identity (61% CPs and 47% in the nucleotide- binding protein [NaBp] region) to that of Melon yellowing-associated virus (MYaV), a typical Carlavirus.

Phylogeographic analysis of the full genome of Sweepovirus to trace virus dispersal and introduction to Korea

Sweet potato is a vegetatively propagated crop that is produced for both growth in Korean fields and for export out of the country. The viruses that are present in introduced sweet potatoes can spread both domestically and to foreign countries. Determining the time and path of virus movement could help curtail its spread and prevent future dispersal of related viruses. Determining the consequences of past virus and sweet potato dispersal could provide insight into the ecological and economic risks associated with other sweet potato-infecting viral invasions. We therefore applied Bayesian phylogeographic inferences and recombination analyses of the available Sweepovirus sequences (including 25 Korean Sweepovirus genomes) and reconstructed a plausible history of Sweepovirus diversification and movement across the globe. The Mediterranean basin and Central America were found to be the launchpad of global Sweepovirus dispersal. Currently, China and Brazil are acting as convergence regions for Sweepoviruses. Recently reported Korean Sweepovirus isolates were introduced from China in a recent phase and the regions around China and Brazil continue to act as centers of Sweepovirus diversity and sites of ongoing Sweepovirus evolution. The evidence indicates that the region is an epidemiological hotspot, which suggests that novel Sweepovirus variants might be found.

Phylogenetic Characterization of Tomato chlorosis virus Population in Korea: Evidence of Reassortment between Isolates from Different Origins

Tomato chlorosis virus (ToCV) is a whitefly-transmitted and phloem-limited crinivirus. In 2013, severe interveinal chlorosis and bronzing on tomato leaves, known symptoms of ToCV infection, were observed in greenhouses in Korea. To identify ToCV infection in symptomatic tomato plants, RT-PCR with ToCV-specific primers was performed on leaf samples collected from 11 tomato cultivating areas where ToCV-like symptoms were observed in 2013 and 2014. About half of samples (45.18%) were confirmed as ToCV-infected, and the complete genome of 10 different isolates were characterized. This is the first report of ToCV occurring in Korea. The phylogenetic relationship and genetic variation among ToCV isolates from Korea and other countries were also analysed. When RNA1 and RNA2 are analysed separately, ToCV isolates were clustered into three groups in phylogenetic trees, and ToCV Korean isolates were confirmed to belong to two groups, which were geographically separated. These results suggested that Korean ToCV isolates originated from two independent origins. However, the RNA1 and RNA2 sequences of the Yeonggwang isolate were confirmed to belong to different groups, which indicated that ToCV RNA1 and RNA2 originated from two different origins and were reassorted in Yeonggwang, which is the intermediate point of two geographically separated groups.

Molecular dissection of distinct symptoms induced by tomato chlorosis virus and tomato yellow leaf curl virus based on comparative transcriptome analysis

The viral infection of plants may cause various physiological symptoms associated with the reprogramming of plant gene expression. However, the molecular mechanisms and associated genes underlying disease symptom development in plants infected with viruses are largely unknown. In this study, we employed RNA sequencing for in-depth molecular characterization of the transcriptional changes associated with the development of distinct symptoms induced by tomato chlorosis virus (ToCV) and tomato yellow leaf curl virus (TYLCV) in tomato. Comparative analysis of differentially expressed genes revealed that ToCV and TYLCV induced distinct transcriptional changes in tomato and resulted in the identification of important genes responsible for the development of symptoms of ToCV (i.e., chlorosis and anthocyanin accumulation) and TYLCV (i.e., yellowing, stunted growth, and leaf curl). Our comprehensive transcriptome analysis can provide molecular strategies to reduce the severity of disease symptoms as well as new insights for the development of virus-resistant crops.

Isolation and validation of a candidate Rsv3 gene from a soybean genotype that confers strain-specific resistance to soybean mosaic virus

Soybean mosaic virus (SMV), a member of the genus Potyvirus, significantly reduces soybean production worldwide. Rsv3, which confers strain-specific resistance to SMV, was previously mapped between the markers A519F/R and M3Satt in chromosome 14 of the soybean [Glycine max (L.) Merr.] genotype L29. Analysis of the soybean genome database revealed that five different NBS-LRR sequences exist between the flanking markers. Among these candidate Rsv3 genes, the full-length cDNA of the Glyma.14g204700 was successfully cloned from L29. Over-expression of Glyma.14g204700 in leaves inoculated with SMV inhibited viral infection in a soybean genotype lacking Rsv3. In addition, the transient silencing of the candidate gene caused a high accumulation of an avirulent strain in L29 carrying Rsv3. Our results therefore provide additional line of evidence to support that Glyma.14g204700 is likely Rsv3 gene that confers strain-specific resistance to SMV.

Movement protein of broad bean wilt virus 2 serves as a determinant of symptom severity in pepper

Broad bean wilt virus 2 (BBWV2, genus Fabavirus, family Secoviridae) has a wide host range and infects many economically important crops. Various isolates of BBWV2 have been identified from diverse host plants, and their molecular and biological characteristics have been investigated. In our previous study, we demonstrated that BBWV2 RNA2 contains a symptom determinant(s) capable of enhancing symptom severity by utilizing infectious full-length cDNA clones of two distinct strains of BBWV2, pBBWV2-PAP1 (a severe strain) and pBBWV2-RP1 (a mild strain). In the present study, to identify the symptom determinant(s) of BBWV2, we exploited disease responses of pBBWV2-PAP1- and pBBWV2-RP1-derived chimeric viruses and amino acid substitution mutant viruses in Nicotiana benthamiana and pepper (Capsicum annuum Quarri) and demonstrated that the movement protein (MP) encoded in BBWV RNA2 is the determinant of disease symptom severity in both plants. A single amino acid substitution in the MP was sufficient for changing symptom severity of BBWV2. Our finding provides a role for the MP as a symptom determinant in BBWV2 and increases the understanding of the basis of molecular interactions between host plants and BBWV2.

Virus Incidence of Sweet Potato in Korea from 2011 to 2014

A nationwide survey was performed to investigate the current incidence of viral diseases in Korean sweet potatoes for germplasm and growing fields from 2011 to 2014. A total of 83.8% of the germplasm in Korea was infected with viruses in 2011. Commercial cultivars that were used to supply growing fields were infected at a rate of 62.1% in 2012. Among surveyed viruses, the incidence of five Potyvirus species that infect sweet potato decreased between 2012 and 2013, and then increased again in 2014. Representatively, the incidence of Sweet potato feathery mottle virus (SPFMV) was 87.0% in 2012, 20.7% in 2013 and then increased to 35.3% in 2014. Unlike RNA viruses, DNA viruses were shown to decrease continuously. The incidence of Sweet potato leaf curl virus (SPLCV) was 5.5% in 2003, 59.5% in 2011, and 47.4% in 2012. It then decreased continuously year by year to 33.2% in 2013, and then 25.6% in 2014. While the infection rate of each virus species showed a tendency to decline, the virus infection status was more variable in 2013 and 2014. Nevertheless, the high rate of single infections and mixed infection combinations were more variable than the survey results from 2012. As shown in the results from 2013, the most prevalent virus infection was a single infection at 27.6%, with the highest rate of infection belonging to sweet potato symptomless virus-1 (SPSMV-1) (12.9%). Compared to 2013, infection combinations were more varied in 2014, with a total of 122 kinds of mixed infection.

Silencing of AtRAP, a target gene of a bacteria-induced small RNA, triggers antibacterial defense responses through activation of LSU2 and down-regulation of GLK1

Plants fine-tune their sophisticated immunity systems in response to pathogen infections. We previously showed that AtlsiRNA-1, a bacteria-induced plant endogenous small interfering RNA, silences the AtRAP gene, which encodes a putative RNA binding protein. In this study, we demonstrate that AtRAP functions as a negative regulator in plant immunity by characterizing molecular and biological responses of the knockout mutant and overexpression lines of AtRAP upon bacterial infection. AtRAP is localized in chloroplasts and physically interacts with Low Sulfur Upregulated 2 (LSU2), which positively regulates plant defense. Our results suggest that AtRAP negatively regulates defense responses by suppressing LSU2 through physical interaction. We also detected downregulation of the transcription factor GOLDEN2-LIKE 1 (GLK1) in atrap-1 using microarray analysis. The glk1 glk2 double mutant showed enhanced resistance to Pseudomonas syringae pv. tomato, which is consistent with a previous study showing enhanced resistance of a glk1 glk2 double mutant to Hyaloperonospora arabidopsidis. Taken together, our data suggest that silencing of AtRAP by AtlsiRNA-1 upon bacterial infection triggers defense responses through regulation of LSU2 and GLK1.

Efficient Transmission and Propagation of Tomato Chlorosis Virus by Simple Single-Leaflet Grafting

Tomato chlorosis virus (ToCV), a member of the genus Crinivirus, has caused an epidemic disease in tomato worldwide. ToCV is phloem-limited and transmitted by whiteflies in a semi-persistent manner, but not by mechanical inoculation. Experimental propagation of ToCV has been performed primarily by using whitefly-mediated inoculation. To develop a simple and convenient method for transmission of ToCV, we investigated grafting single-leaflets from tomato plants infected with ToCV to recipient tomato seedlings. Forty-one of 46 tomato seedlings tested were grafted successfully with single-leaflets infected with ToCV. Among them, 36 seedlings (87.8%) were systemically infected with ToCV and developed typical symptoms. Our results demonstrated that single-leaflet grafting could provide a sufficient amount of inoculum for the transmission of ToCV to the grafted seedlings.

Complete genome sequence of longan witches' broom-associated virus, a novel member of the family Potyviridae

The complete genome sequence of a new virus isolated from a longan (Dimocarpus longan Lour.) plant showing witches' broom syndrome was determined. The viral genome is composed of a monopartite single-stranded RNA of 9,428 nucleotides excluding the 3' poly(A) tail and contains one large single open reading frame encoding a polyprotein of 3086 amino acids. BLAST searches of protein databases showed that the encoded polyprotein has a maximum amino acid sequence identity of 35% (with 85% coverage) to that of the isolate Minnesota of rose yellow mosaic virus (RoYMV; family Potyviridae; genus not assigned). Molecular and phylogenetic analysis of the genome and encoded protein sequences showed that the identified virus has the general features that are characteristic of members of the family Potyviridae although it has extremely low sequence similarity to known members of the family Potyviridae. The name longan witches' broom-associated virus (LWBaV) is proposed for this new virus, which may be considered a member of a new genus in the family Potyviridae.

Engineering of soybean mosaic virus as a versatile tool for studying protein-protein interactions in soybean

Transient gene expression approaches are valuable tools for rapid introduction of genes of interest and characterization of their functions in plants. Although agroinfiltration is the most effectively and routinely used method for transient expression of multiple genes in various plant species, this approach has been largely unsuccessful in soybean. In this study, we engineered soybean mosaic virus (SMV) as a dual-gene delivery vector to simultaneously deliver and express two genes in soybean cells. We further show the application of the SMV-based dual vector for a bimolecular fluorescence complementation assay to visualize in vivo protein-protein interactions in soybean and for a co-immunoprecipitation assay to identify cellular proteins interacting with SMV helper component protease. This approach provides a rapid and cost-effective tool for transient introduction of multiple traits into soybean and for in vivo characterization of the soybean cellular protein interaction network.

Identification of Leonurus sibiricus as a Weed Reservoir for Three Pepper-Infecting Viruses

In plant virus ecology, weeds are regarded as wild reservoirs of viruses and as potential sources for insect-mediated transmission of viruses. During field surveys in 2013-2014, three Leonurus sibiricus plants showing virus-like symptoms were collected from pepper fields in Daegu, Seosan, and Danyang in Korea. Molecular diagnosis assays showed that the collected L. sibiricus samples were infected with either Tomato spotted wilt virus (TSWV), Pepper mild mottle virus (PMMoV), or Beet western yellow virus (BWYV), respectively. Since this is the first identification of TSWV, PMMoV, and BWYV from L. sibiricus, complete genome sequences of three virus isolates were determined to examine their phylogenetic relationships with the previously reported strains and isolates. Phylogenetic analyses performed using full genome sequences of the viruses showed the isolates of TSWV and PMMoV obtained from L. sibiricus are closely related to the pepper isolates of the corresponding viruses. Our results suggest that L. sibiricus could act an alternative host and reservoir of viruses that cause damages in pepper fields.

Establishment of a Simple and Rapid Gene Delivery System for Cucurbits by Using Engineered of Zucchini yellow mosaic virus

The infectious full-length cDNA clone of zucchini yellow mosaic virus (ZYMV) isolate PA (pZYMV-PA), which was isolated from pumpkin, was constructed by utilizing viral transcription and processing signals to produce infectious in vivo transcripts. Simple rub-inoculation of plasmid DNAs of pZYMV-PA was successful to cause infection of zucchini plants (Cucurbita pepo L.). We further engineered this infectious cDNA clone of ZYMV as a viral vector for systemic expression of heterologous proteins in cucurbits. We successfully expressed two reporter genes including gfp and bar in zucchini plants by simple rub-inoculation of plasmid DNAs of the ZYMV-based expression constructs. Our method of the ZYMV-based viral vector in association with the simple rub-inoculation provides an easy and rapid approach for introduction and evaluation of heterologous genes in cucurbits.

A determinant of disease symptom severity is located in RNA2 of broad bean wilt virus 2

Broad bean wilt virus 2 (BBWV2), which belongs to the genus Fabavirus, is a destructive pathogen of many economically important horticultural and ornamental crops. In this study, we constructed infectious full-length cDNA clones of two distinct isolates of BBWV2 under control of the cauliflower mosaic virus 35S promoter. BBWV2-PAP1 isolated from paprika (Capsicum annuum var. gulosum) induces severe disease symptoms in various pepper varieties, whereas BBWV2-RP1 isolated from red pepper (Capsicum annuum L.) causes mild symptoms. Agrobacterium-mediated inoculation of the infectious cDNA clones of BBWV2-PAP1 and RP1 resulted in the same symptoms as the original virus isolates. The infectious cDNA clones of BBWV2-PAP1 and RP1 were used to examine the symptoms induced by pseudorecombinants between the two isolates to localize in which of the two genomic RNAs are the symptom severity determinants in BBWV2. The pseudorecombinant of RP1-RNA1 and PAP1-RNA2 induced severe symptoms, similar to those caused by the parental isolate PAP1, whereas the pseudorecombinant of PAP1-RNA1 and RP1-RNA2 induced mild symptoms, similar to those caused by the parental isolate RP1. Our results suggest that BBWV2 RNA2 contains a symptom determinant(s) capable of enhancing symptom severity.

Establishment of an Agrobacterium-mediated Inoculation System for Cucumber Green Mottle Mosaic Virus

The infectious full-length cDNA clones of Cucumber green mottle mosaic virus (CGMMV) isolates KW and KOM, which were isolated from watermelon and oriental melon, respectively, were constructed under the control of the cauliflower mosaic virus 35S promoter. We successfully inoculated Nicotiana benthamiana with the cloned CGMMV isolates KW and KOM by Agrobacterium-mediated infiltration. Virulence and symptomatic characteristics of the cloned CGMMV isolates KW and KOM were tested on several indicator plants. No obvious differences between two cloned isolates in disease development were observed on the tested indicator plants. We also determined full genome sequences of the cloned CGMMV isolates KW and KOM. Sequence comparison revealed that only four amino acids (at positions 228, 699, 1212, and 1238 of the replicase protein region) differ between the cloned isolates KW and KOM. A previous study reported that the isolate KOM could not infect Chenopodium amaranticolor, but the cloned KOM induced chlorotic spots on the inoculated leaves. When compared with the previously reported sequence of the original KOM isolate, the cloned KOM contained one amino acid mutation (Ala to Thr) at position 228 of the replicase protein, suggesting that this mutation might be responsible for induction of chlorotic spots on the inoculated leaves of C. amaranticolor.

Molecular Characterization of Five Potyviruses Infecting Korean Sweet Potatoes Based on Analyses of Complete Genome Sequences

Sweet potatoes (Ipomea batatas L.) are grown extensively, in tropical and temperate regions, and are important food crops worldwide. In Korea, potyviruses, including Sweet potato feathery mottle virus (SPFMV), Sweet potato virus C (SPVC), Sweet potato virus G (SPVG), Sweet potato virus 2 (SPV2), and Sweet potato latent virus (SPLV), have been detected in sweet potato fields at a high (~95%) incidence. In the present work, complete genome sequences of 18 isolates, representing the five potyviruses mentioned above, were compared with previously reported genome sequences. The complete genomes consisted of 10,081 to 10,830 nucleotides, excluding the poly-A tails. Their genomic organizations were typical of the Potyvirus genus, including one target open reading frame coding for a putative polyprotein. Based on phylogenetic analyses and sequence comparisons, the Korean SPFMV isolates belonged to the strains RC and O with >98% nucleotide sequence identity. Korean SPVC isolates had 99% identity to the Japanese isolate SPVC-Bungo and 70% identity to the SPFMV isolates. The Korean SPVG isolates showed 99% identity to the three previously reported SPVG isolates. Korean SPV2 isolates had 97% identity to the SPV2 GWB-2 isolate from the USA. Korean SPLV isolates had a relatively low (88%) nucleotide sequence identity with the Taiwanese SPLV-TW isolates, and they were phylogenetically distantly related to SPFMV isolates. Recombination analysis revealed that possible recombination events occurred in the P1, HC-Pro and NIa-NIb regions of SPFMV and SPLV isolates and these regions were identified as hotspots for recombination in the sweet potato potyviruses.

Complete genome sequence of bellflower vein chlorosis virus, a novel putative member of the genus Waikavirus

The complete genome sequence of a new virus isolated from a bellflower (Campanula takesimana) plant was determined. The genome of this virus is composed of monopartite single-stranded RNA of 11,649 nucleotides in length. BLAST searches of protein databases showed that the encoded polyprotein has a maximum amino acid sequence identity of 42% (with 99% coverage) to the polyprotein of the isolate Orissa of rice tungro spherical virus (RTSV; genus Waikavirus). Phylogenetic analysis strongly supports that the identified virus is a member of a new species of the genus Waikavirus. The name bellflower vein chlorosis virus (BVCV) is proposed for this new virus.

Detection of admittivity anomaly on high-contrast heterogeneous backgrounds using frequency difference EIT

This paper describes a multiple background subtraction method in frequency difference electrical impedance tomography (fdEIT) to detect an admittivity anomaly from a high-contrast background conductivity distribution. The proposed method expands the use of the conventional weighted frequency difference EIT method, which has been used limitedly to detect admittivity anomalies in a roughly homogeneous background. The proposed method can be viewed as multiple weighted difference imaging in fdEIT. Although the spatial resolutions of the output images by fdEIT are very low due to the inherent ill-posedness, numerical simulations and phantom experiments of the proposed method demonstrate its feasibility to detect anomalies. It has potential application in stroke detection in a head model, which is highly heterogeneous due to the skull.

The current incidence of viral disease in korean sweet potatoes and development of multiplex rt-PCR assays for simultaneous detection of eight sweet potato viruses

Sweet potato is grown extensively from tropical to temperate regions and is an important food crop worldwide. In this study, we established detection methods for 17 major sweet potato viruses using single and multiplex RT-PCR assays. To investigate the current incidence of viral diseases, we collected 154 samples of various sweet potato cultivars showing virus-like symptoms from 40 fields in 10 Korean regions, and analyzed them by RT-PCR using specific primers for each of the 17 viruses. Of the 17 possible viruses, we detected eight in our samples. Sweet potato feathery mottle virus (SPFMV) and sweet potato virus C (SPVC) were most commonly detected, infecting approximately 87% and 85% of samples, respectively. Furthermore, Sweet potato symptomless virus 1 (SPSMV-1), Sweet potato virus G (SPVG), Sweet potato leaf curl virus (SPLCV), Sweet potato virus 2 ( SPV2), Sweet potato chlorotic fleck virus (SPCFV), and Sweet potato latent virus (SPLV) were detected in 67%, 58%, 47%, 41%, 31%, and 20% of samples, respectively. This study presents the first documented occurrence of four viruses (SPVC, SPV2, SPCFV, and SPSMV-1) in Korea. Based on the results of our survey, we developed multiplex RT-PCR assays for simple and simultaneous detection of the eight sweet potato viruses we recorded.

Complete genome sequence of motherwort yellow mottle virus, a novel putative member of the genus Torradovirus

The complete genome sequence of a new virus isolated from a motherwort plant exhibiting yellow mottle, mild mosaic, and stunting symptoms in Andong, Korea, was determined. The genome of this virus is composed of two single-stranded RNAs (7068 and 4963 nucleotides in length, respectively) carrying poly(A) tails. RNA1 contains one large open reading frame (RNA1-ORF1), while two potential ORFs (RNA2-ORF1 and RNA2-ORF2) were found in RNA2. BLAST searches of protein databases showed that RNA1-ORF1 and RNA2-ORF2 have maximum amino acid sequence identities of 53 % and 57 % to the RNA1-ORF1 and RNA2-ORF2, respectively, of lettuce necrotic leaf curl virus (LNLCV, a recently identified torradovirus). Phylogenetic analysis provided further evidence that the virus identified in this study is probably a member of a new species in the genus Torradovirus. The name "motherwort yellow mottle virus" (MYMoV) is proposed for this new virus.

Molecular genetic analysis of cucumber mosaic virus populations infecting pepper suggests unique patterns of evolution in Korea

Studying genetic structure and diversity of viruses is important to understand the evolutionary mechanisms that generate and maintain variations in viral populations. Cucumber mosaic virus (CMV) is endemic in most pepper fields in Korea. Currently, no effective methods for control of CMV are available due to many environmental and biological factors such as the extensive evolutionary capacity of CMV. Thus, analyzing the genetic structure of CMV populations may facilitate the development of strategies for the control of CMV. In this study, 252 pepper (Capsicum annuum) samples showing virus symptoms were collected by field surveys performed throughout Korea in 2007. Reverse-transcription polymerase chain reaction analyses revealed that, in total, 165 collected samples were infected with CMV. Forty-five CMV isolates were randomly selected within each regional subpopulation and analyzed by full-genome sequencing. Analyses of genetic diversity showed that the 2b gene of CMV is under weaker purifying selection than the other genes. Based on the phylogenetic analysis of RNA1, the CMV isolates from pepper were divided into three clusters in subgroup I. Our full-genome sequence-based molecular analyses of the CMV Korean population suggest that the subpopulations of CMV have been geographically localized in pepper fields in Korea.

Pseudorecombination between Two Distinct Strains of Cucumber mosaic virus Results in Enhancement of Symptom Severity

Recently, a Cucumber mosaic virus (CMV) strain, named as CMV-209, was isolated from Glycine soja. In this study, symptom expression of CMV-209 was analyzed in detail in Nicotiana benthamiana by comparing with that of CMV-Fny, which is a representative strain of CMV. Using infectious cDNA clones of CMV strains 209 and Fny, symptom expression of various pseudorecombinants between these two strains were examined in the early and late infection stages. In the early infection stage, the pseudorecombinants containing Fny-RNA2 induced stunting and leaf distortion on the newly emerged leaves whereas the pseudorecombinants containing 209-RNA2 caused no obvious symptoms. In the late infection stage, the pseudorecombinants containing 209-RNA1 and Fny-RNA2 induced severe leaf distortion and stunting, while CMV-209 induced mild symptom and CMV-Fny caused typical mosaic, general stunting, and leaf distortion symptoms, indicating that RNA 2 encodes a symptom determinant(s) of CMV, which is capable of enhancing symptoms. Furthermore, our results support the possibility that natural recombination between compatible viruses can result in emergence of novel viruses causing severe damages in crop fields.

Type 2C protein phosphatase is a key regulator of antiviral extreme resistance limiting virus spread

Effector-triggered immunity (ETI) is an active immune response triggered by interactions between host resistance proteins and their cognate effectors. Although ETI is often associated with the hypersensitive response (HR), various R genes mediate an HR-independent process known as extreme resistance (ER). In the soybean-Soybean mosaic virus (SMV) pathosystem, the strain-specific CI protein of SMV functions as an effector of Rsv3-mediated ER. In this study, we used the soybean (Rsv3)-SMV (CI) pathosystem to gain insight into the molecular signaling pathway involved in ER. We used genome-wide transcriptome analysis to identify a subset of the type 2C protein phophatase (PP2C) genes that are specifically up-regulated in Rsv3-mediated ER. Gain-of-function analysis of the most significantly expressed soybean PP2C gene, GmPP2C3a, showed that ABA-induced GmPP2C3a functions as a key regulator of Rsv3-mediated ER. Our results further suggest that the primary mechanism of ER against viruses is the inhibition of viral cell-to-cell movement by callose deposition in an ABA signaling-dependent manner.

Characterization of Cellulolytic and Xylanolytic Enzymes of Bacillus licheniformis JK7 Isolated from the Rumen of a Native Korean Goat

A facultative bacterium producing cellulolytic and hemicellulolytic enzymes was isolated from the rumen of a native Korean goat. The bacterium was identified as a Bacillus licheniformis on the basis of biochemical and morphological characteristics and 16S rDNA sequences, and has been designated Bacillus licheniformis JK7. Endoglucanase activities were higher than those of β-glucosidase and xylanase at all temperatures. Xylanase had the lowest activity among the three enzymes examined. The optimum temperature for the enzymes of Bacillus licheniformis JK7 was 70°C for endoglucanase (0.75 U/ml) and 50°C for β-glucosidase and xylanase (0.63 U/ml, 0.44 U/ml, respectively). All three enzymes were stable at a temperature range of 20 to 50°C. At 50°C, endoglucanse, β-glucosidase, and xylanase had 90.29, 94.80, and 88.69% residual activity, respectively. The optimal pH for the three enzymes was 5.0, at which their activity was 1.46, 1.10, and 1.08 U/ml, respectively. The activity of all three enzymes was stable in the pH range of 3.0 to 6.0. Endoglucanase activity was increased 113% by K⁺, while K⁺, Zn⁺, and tween 20 enhanced β-glucosidase activity. Xylanase showed considerable activity even in presence of selected chemical additives, with the exception of Mn²⁺ and Cu²⁺. The broad range of optimum temperatures (20 to 40°C) and the stability under acidic pH (4 to 6) suggest that the cellulolytic enzymes of Bacillus licheniformis JK7 may be good candidates for use in the biofuel industry.

Molecular and Biological Characterization of an Isolate of Cucumber mosaic virus from Glycine soja by Generating its Infectious Full-genome cDNA Clones

Molecular and biological characteristics of an isolate of Cucumber mosaic virus (CMV) from Glycine soja (wild soybean), named as CMV-209, was examined in this study. Comparison of nucleotide sequences and phylogenetic analyses of CMV-209 with the other CMV strains revealed that CMV-209 belonged to CMV subgroup I. However, CMV-209 showed some genetic distance from the CMV strains assigned to subgroup IA or subgroup IB. Infectious full-genome cDNA clones of CMV-209 were generated under the control of the Cauliflower mosaic virus 35S promoter. Infectivity of the CMV-209 clones was evaluated in Nicotiana benthamiana and various legume species. Our assays revealed that CMV-209 could systemically infect Glycine soja (wild soybean) and Pisum sativum (pea) as well as N. benthamiana, but not the other legume species.

A novel set of polyvalent primers that detect members of the genera Bromovirus and Cucumovirus

Rapid detection and diagnosis of plant virus infection is one of the most important steps in preventing damages caused by viral diseases. Bromoviruses and cucumoviruses belong to the family Bromoviridae, which is one of the most important families of plant viruses, and infect a broad range of host plants including various economically important crops. In this study, an RT-PCR assay was developed for the universal detection of bromoviruses and cucumoviruses using a set of primers designed to target the conserved sequences in viral RNA1. The assay detected three species of Cucumovirus (Cucumber mosaic virus (CMV), Peanut stunt virus (PSV) and Tomato aspermy virus (TAV)) and two species of Bromovirus (Brome mosaic virus (BMV) and Cowpea chlorotic mottle virus (CCMV)) with high specificity and sensitivity. The assay developed in this study is predicted to have the potential to detect all major members of the genera Bromovirus and Cucumovirus and to be used as a routine diagnostic assay.

Molecular Characterization and Variation of the Broad bean wilt virus 2 Isolates Based on Analyses of Complete Genome Sequences

The full-genome sequences of fourteen isolates of Broad bean wilt virus 2 (BBWV2), collected from broad bean, pea, spinach, bell pepper and paprika plants in Korea during the years 2006-2012, were determined and analyzed comparatively along with fifteen previously reported BBWV2 genome sequences. Sequence analyses showed that RNA-1 and RNA-2 sequences of BBWV2 Korean isolates consisted of 5950-5956 and 3568-3604 nucleotides, respectively. Full-length genome sequence-based phylogenetic analyses revealed that the BBWV2 Korean isolates could be divided into three major groups comprising GS-I (isolates BB2 and RP7) along with isolate IP, GS-II (isolates BB5, P2, P3 and RP3) along with isolate B935, and GS-III including 16 BBWV2 Korean isolates. Interestingly, GS-III appears to be newly emerged and predominant in Korea. Recombination analyses identified two recombination events in the analyzed BBWV2 population: one in the RNA-1 of isolate K and another one in the RNA-2 of isolate XJ14-3. However, no recombination events were detected in the other 21 Korean isolates. On the other hand, out of 29 BBWV2 isolates, 16 isolates were found to be reassortants, of which each RNA segment (i.e. RNA1 and RNA2) was originated from different parental isolates. Our findings suggested that reassortment rather than recombination is a major evolutionary force in the genetic diversification of BBWV population in Korea.