Investigation of CaMV-host co-evolution through synonymous codon pattern

Cauliflower mosaic virus (CaMV) has a double-stranded DNA genome and is globally distributed. The phylogeny tree of 121 CaMV isolates was categorized into two primary groups, with Iranian isolates showing the greatest genetic variations. Nucleotide A demonstrated the highest percentage (36.95%) in the CaMV genome and the dinucleotide odds ratio analysis revealed that TC dinucleotide (1.34 ≥ 1.23) and CG dinucleotide (0.63 ≤ 0.78) are overrepresented and underrepresented, respectively. Relative synonymous codon usage (RSCU) analysis confirmed codon usage bias in CaMV and its hosts. Brassica oleracea and Brassica rapa, among the susceptible hosts of CaMV, showed a codon adaptation index (CAI) value above 0.8. Additionally, relative codon deoptimization index (RCDI) results exhibited the highest degree of deoptimization in Raphanus sativus. These findings suggest that the genes of CaMV underwent codon adaptation with its hosts. Among the CaMV open reading frames (ORFs), genes that produce reverse transcriptase and virus coat proteins showed the highest CAI value of 0.83. These genes are crucial for the creation of new virion particles. The results confirm that CaMV co-evolved with its host to ensure the optimal expression of its genes in the hosts, allowing for easy infection and effective spread. To detect the force behind codon usage bias, an effective number of codons (ENC)-plot and neutrality plot were conducted. The results indicated that natural selection is the primary factor influencing CaMV codon usage bias.

The Carboxyl Terminal Regions of P0 Protein Are Required for Systemic Infections of Poleroviruses

P0 proteins encoded by poleroviruses Brassica yellows virus (BrYV) and Potato leafroll virus (PLRV) are viral suppressors of RNA silencing (VSR) involved in abolishing host RNA silencing to assist viral infection. However, other roles that P0 proteins play in virus infection remain unclear. Here, we found that C-terminal truncation of P0 resulted in compromised systemic infection of BrYV and PLRV. C-terminal truncation affected systemic but not local VSR activities of P0 proteins, but neither transient nor ectopic stably expressed VSR proteins could rescue the systemic infection of BrYV and PLRV mutants. Moreover, BrYV mutant failed to establish systemic infection in DCL2/4 RNAi or RDR6 RNAi plants, indicating that systemic infection might be independent of the VSR activity of P0. Partially rescued infection of BrYV mutant by the co-infected PLRV implied the functional conservation of P0 proteins within genus. However, although C-terminal truncation mutant of BrYV P0 showed weaker interaction with its movement protein (MP) when compared to wild-type P0, wild-type and mutant PLRV P0 showed similar interaction with its MP. In sum, our findings revealed the role of P0 in virus systemic infection and the requirement of P0 carboxyl terminal region for the infection.

Concatemeric Broccoli reduces mRNA stability and induces aggregates

Fluorogenic aptamers are an alternative to established methodology for real-time imaging of RNA transport and dynamics. We developed Broccoli-aptamer concatemers ranging from 4 to 128 substrate-binding site repeats and characterized their behavior fused to an mCherry-coding mRNA in transient transfection, stable expression, and in recombinant cytomegalovirus infection. Concatemerization of substrate-binding sites increased Broccoli fluorescence up to a concatemer length of 16 copies, upon which fluorescence did not increase and mCherry signals declined. This was due to the combined effects of RNA aptamer aggregation and reduced RNA stability. Unfortunately, both cellular and cytomegalovirus genomes were unable to maintain and express high Broccoli concatemer copy numbers, possibly due to recombination events. Interestingly, negative effects of Broccoli concatemers could be partially rescued by introducing linker sequences in between Broccoli repeats warranting further studies. Finally, we show that even though substrate-bound Broccoli is easily photobleached, it can still be utilized in live-cell imaging by adapting a time-lapse imaging protocol.

The complete genome sequence of a new mitovirus from the phytopathogenic fungus Colletotrichum higginsianum

In this study, a novel mitovirus designed "Colletotrichum higginsianum mitovirus 1" (ChMV1) was isolated from the phytopathogenic fungus Colletotrichum higginsianum. The genome of this mitovirus is 2,893 nt in length with an A + U content of 61% and contains a large open reading frame (ORF) encoding an RNA-dependent RNA polymerase (RdRp). A BLASTp analysis revealed that the RdRp domain of ChMV1 had 30.25% to 61.72% sequence identity to those of members of the genus Mitovirus and showed the highest degree of similarity (61.72% identity) to Botrytis cinerea mitovirus 3 (BcMV3). Phylogenetic analysis further indicated that ChMV1 is a member in the genus Mitovirus of the family Mitoviridae. To the best of our knowledge, this is the first report of a mitovirus in C. higginsianum.

A 2-kb Mycovirus Converts a Pathogenic Fungus into a Beneficial Endophyte for Brassica Protection and Yield Enhancement

Mycoviruses are viruses that infect fungi, and hypovirulence-associated mycoviruses have the potential to control fungal diseases. However, it is unclear how mycovirus-mediated hypovirulent strains live and survive in the field, and no mycovirus has been applied for field crop protection. In this study, we found that a previously identified small DNA mycovirus (SsHADV-1) can convert its host, Sclerotinia sclerotiorum, from a typical necrotrophic pathogen to a beneficial endophytic fungus. SsHADV-1 downregulates the expression of key pathogenicity factor genes in S. sclerotiorum during infection. When growing in rapeseed, the SsHADV-1-infected strain DT-8 significantly regulates the expression of rapeseed genes involved in defense, hormone signaling, and circadian rhythm pathways. As a result, plant growth is promoted and disease resistance is enhanced. Field experiments showed that spraying DT-8 at the early flowering stage can reduce the disease severity of rapeseed stem rot by 67.6% and improve yield by 14.9%. Moreover, we discovered that SsHADV-1 could also infect other S. sclerotiorum strains on DT-8-inoculated plants and that DT-8 could be recovered from dead plants. These findings suggest that the mycoviruses may have the ability to shape the origin of endophytism. Our discoveries suggest that mycoviruses may influence the origin of endophytism and may also offer a novel strategy for disease control in which mycovirus-infected strains are used to improve crop health and release mycoviruses into the field.

An efficient virus-induced gene silencing (VIGS) system for functional genomics in Brassicas using a cabbage leaf curl virus (CaLCuV)-based vector

CaLCuV-based VIGS effectively works in cabbage and contributes to efficient functional genomics research in Brassica crop species. Virus-induced gene silencing (VIGS), a posttranscriptional gene silencing method, is an effective technique for analysing the functions of genes in plants. However, no VIGS vectors have been available for Brassica oleracea until now. Here, tobacco rattle virus (TRV), pTYs and cabbage leaf curl virus (CaLCuV) gene-silencing vectors (PCVA/PCVB) were chosen to improve the VIGS system in cabbage using the phytoene desaturase (PDS) gene as an efficient visual indicator of VIGS. We successfully silenced the expression of PDS and observed photobleaching phenomena in cabbage in response to pTYs and CaLCuV, with the latter being more easy to operate and less expensive. The parameters potentially affecting the silencing efficiency of VIGS by CaLCuV in cabbage, including the targeting fragment strategy, inoculation method and incubation temperature, were then compared. The optimized CaLCuV-based VIGS system involves the following: an approximately 500 bp insert sequence, an Agrobacterium OD₆₀₀ of 1.0, use of the vacuum osmosis method applied at the bud stage, and an incubation temperature of 22 °C. Using these parameters, we achieved a stable silencing efficiency of 65%. To further test the effectiveness of the system, we selected the Mg-chelatase H subunit (ChlH) gene in cabbage and knocked down its expression, and we observed yellow leaves, as expected. We successfully applied the CaLCuV-based VIGS system to two other representative Brassica crop species, B. rapa and B. nigra, and thus expanded the application scope of this system. Our VIGS system described here will contribute to efficient functional genomics research in Brassica crop species.

A novel formulation technology for baculoviruses protects biopesticide from degradation by ultraviolet radiation

Biopesticides are biological pest control agents that are viewed as safer alternatives to the synthetic chemicals that dominate the global insecticide market. A major constraint on the wider adoption of biopesticides is their susceptibility to the ultraviolet (UV: 290-400 nm) radiation in sunlight, which limits their persistence and efficacy. Here, we describe a novel formulation technology for biopesticides in which the active ingredient (baculovirus) is micro-encapsulated in an ENTOSTAT wax combined with a UV absorbant (titanium dioxide, TiO2). Importantly, this capsule protects the sensitive viral DNA from degrading in sunlight, but dissolves in the alkaline insect gut to release the virus, which then infects and kills the pest. We show, using simulated sunlight, in both laboratory bioassays and trials on cabbage and tomato plants, that this can extend the efficacy of the biopesticide well beyond the few hours of existing virus formulations, potentially increasing the spray interval and/or reducing the need for high application rates. The new formulation has a shelf-life at 30 °C of at least 6 months, which is comparable to standard commercial biopesticides and has no phytotoxic effect on the host plants. Taken together, these findings suggest that the new formulation technology could reduce the costs and increase the efficacy of baculovirus biopesticides, with the potential to make them commercially competitive alternatives to synthetic chemicals.

A Brassica miRNA Regulates Plant Growth and Immunity through Distinct Modes of Action

In plants, high disease resistance often results in a reduction of yield. Therefore, breeding crops with balanced yield and disease resistance has become a major challenge. Recently, microRNA (miRNA)-mediated R gene turnover has been shown to be a protective mechanism used by plants to prevent autoimmunity in the absence of pathogens. However, whether these miRNAs play a role in plant growth and how miRNA-mediated R gene turnover responds to pathogen infection have rarely been explored. Here, we found that a Brassica miRNA, miR1885, targets both an immune receptor gene and a development-related gene for negative regulation through distinct modes of action. MiR1885 directly silences the TIR-NBS-LRR class of R gene BraTNL1 but represses the expression of the photosynthesis-related gene BraCP24 by targeting the Trans-Acting Silencing (TAS) gene BraTIR1 for trans-acting small interfering RNAs (tasiRNAs)-mediated silencing. We found that, under natural conditions, miR1885 was kept at low levels to maintain normal development and basal immunity but peaked during the floral transition to promote flowering. Interestingly, upon Turnip mosaic virus (TuMV) infection, miR1885-dependent trans-acting silencing of BraCP24 was enhanced to speed up the floral transition, whereas miR1885-mediated R gene turnover was overcome by TuMV-induced BraTNL1 expression, reflecting precise regulation of the arms race between plants and pathogens. Collectively, our results demonstrate that a single Brassica miRNA dynamically regulates both innate immunity and plant growth and responds to viral infection, revealing that Brassica plants have developed a sophisticated mechanism in modulating the interplay between growth, immunity, and pathogen infection.

A Turnip Mosaic Virus Determinant of Systemic Necrosis in Nicotiana benthamiana and a Novel Resistance-Breaking Determinant in Chinese Cabbage Identified from Chimeric Infectious Clones

Infectious clones of Korean turnip mosaic virus (TuMV) isolates KIH1 and HJY1 share 88.1% genomic nucleotides and 96.4% polyprotein amino acid identity, and they induce systemic necrosis or mild mosaic, respectively, in Nicotiana benthamiana. Chimeric constructs between these isolates exchanged the 5', central, and 3' domains of KIH1 (K) and HJY1 (H), where the order of the letters indicates the origin of these domains. KIH1 and chimeras KHH and KKH induced systemic necrosis, whereas HJY1 and chimeras HHK, HKK, and HKH induced mild symptoms, indicating the determinant of necrosis to be within the 5' 3.9 kb of KIH1; amino acid identities of the included P1, Helper component protease, P3, 6K1, and cylindrical inclusion N-terminal domain were 90.06, 98.91, 93.80, 100, and 100%, respectively. Expression of P1 or P3 from a potato virus X vector yielded symptom differences only between P3 of KIH1 and HJY1, implicating a role for P3 in necrosis in N. benthamiana. Chimera KKH infected Brassica rapa var. pekinensis 'Norang', which was resistant to both KIH1 and HJY1, indicating that two separate TuMV determinants are required to overcome the resistance. Ability of diverse TuMV isolates, chimeras, and recombinants to overcome resistance in breeding lines may allow identification of novel resistance genes.

Molecular characterization of a new recombinant brassica yellows virus infecting tobacco in China

Brassica yellows virus (BrYV), prevalently distributed throughout mainland China and South Korea while triggering serious diseases in cruciferous crops, is proposed to be a new species in the genus Polerovirus within the family Luteoviridae. There are three distinct genotypes (BrYV-A, BrYV-B and BrYV-C) reported in cabbage and radish. Here, we describe a new BrYV isolate infecting tobacco plants in the field, which was named BrYV-NtabQJ. The complete genome sequence of BrYV-NtabQJ is 5741 nt in length, and 89% of the sequence shares higher sequence identities (about 90%) with different BrYV isolates. However, it possesses a quite divergent region within ORF5, which is more close to Beet western yellows virus (BWYV), Beet mild yellowing virus (BMYV) and Beet chlorosis virus (BChV). A significant recombination event was then detected among BrYV-NtabQJ, BrYV-B Beijng isolate (BrYV-BBJ) and BWYV Leonurus sibiricus isolate (BWYV-LS). It is proposed that BrYV-NtabQJ might be an interspecific recombinant between BrYV-BBJ and BWYV-LS, and the recombination might result in the successful aphid transmission of BrYV from cruciferous crops to tobacco. And it also poses new challenges for BrYV diagnosis and the vegetable production.

The Aphid-Transmitted Turnip yellows virus Differentially Affects Volatiles Emission and Subsequent Vector Behavior in Two Brassicaceae Plants

Aphids are important pests which cause direct damage by feeding or indirect prejudice by transmitting plant viruses. Viruses are known to induce modifications of plant cues in ways that can alter vector behavior and virus transmission. In this work, we addressed whether the modifications induced by the aphid-transmitted Turnip yellows virus (TuYV) in the model plant Arabidopsis thaliana also apply to the cultivated plant Camelina sativa, both belonging to the Brassicaceae family. In most experiments, we observed a significant increase in the relative emission of volatiles from TuYV-infected plants. Moreover, due to plant size, the global amounts of volatiles emitted by C. sativa were higher than those released by A. thaliana. In addition, the volatiles released by TuYV-infected C. sativa attracted the TuYV vector Myzus persicae more efficiently than those emitted by non-infected plants. In contrast, no such preference was observed for A. thaliana. We propose that high amounts of volatiles rather than specific metabolites are responsible for aphid attraction to infected C. sativa. This study points out that the data obtained from the model pathosystem A. thaliana/TuYV cannot be straightforwardly extrapolated to a related plant species infected with the same virus.

Identification of Plant Virus Receptor Candidates in the Stylets of Their Aphid Vectors

Plant viruses transmitted by insects cause tremendous losses in most important crops around the world. The identification of receptors of plant viruses within their insect vectors is a key challenge to understanding the mechanisms of transmission and offers an avenue for future alternative control strategies to limit viral spread. We here report the identification of two cuticular proteins within aphid mouthparts, and we provide experimental support for the role of one of them in the transmission of a noncirculative virus. These two proteins, named Stylin-01 and Stylin-02, belong to the RR-1 cuticular protein subfamily and are highly conserved among aphid species. Using an immunolabeling approach, they were localized in the maxillary stylets of the pea aphid Acyrthosiphon pisum and the green peach aphid Myzus persicae, in the acrostyle, an organ earlier shown to harbor receptors of a noncirculative virus. A peptide motif present at the C termini of both Stylin-01 and Stylin-02 is readily accessible all over the surface of the acrostyle. Competition for in vitro binding to the acrostyle was observed between an antibody targeting this peptide and the helper component protein P2 of Cauliflower mosaic virus Furthermore, silencing the stylin-01 but not stylin-02 gene through RNA interference decreased the efficiency of Cauliflower mosaic virus transmission by Myzus persicae These results identify the first cuticular proteins ever reported within arthropod mouthparts and distinguish Stylin-01 as the best candidate receptor for the aphid transmission of noncirculative plant viruses.IMPORTANCE Most noncirculative plant viruses transmitted by insect vectors bind to their mouthparts. They are acquired and inoculated within seconds when insects hop from plant to plant. The receptors involved remain totally elusive due to a long-standing technical bottleneck in working with insect cuticle. Here we characterize the role of the two first cuticular proteins ever identified in arthropod mouthparts. A domain of these proteins is directly accessible at the surface of the cuticle of the acrostyle, an organ at the tip of aphid stylets. The acrostyle has been shown to bind a plant virus, and we consistently demonstrated that one of the identified proteins is involved in viral transmission. Our findings provide an approach to identify proteins in insect mouthparts and point at an unprecedented gene candidate for a plant virus receptor.

Efficacy of Combination Treatment with Sodium Metasilicate and Sodium Hypochlorite for Inactivation of Norovirus on Fresh Vegetables

In recent years, fresh vegetables have frequently been associated with the foodborne transmission of enteric viruses, such as human norovirus (NoV). Therefore, several studies have focused on developing methods to inactivate foodborne viruses for preventing outbreaks of foodborne illnesses. Sodium hypochlorite (NaOCl) is commonly used as a disinfectant, but results in undesirable effects on the appearance and taste of foods and can generate toxic byproducts when it exceeds the allowable concentration. Here, we evaluated the efficacy of a range of NaOCl concentrations (50-1000 ppm) for reducing the amounts of human NoV (NoV GII.4) on lettuce (Lactuca sativa), celery (Apium graveolens L.), and white cabbage (Brassica oleracea ssp. capitata). In addition, the combination treatment of NaOCl and sodium metasilicate (SMS, 0.1-0.5%) pentahydrate was evaluated for its ability to decrease the populations of NoV GII.4 in the three food samples. An immunomagnetic separation procedure combined with reverse transcription quantitative polymerase chain reaction was used for virus detection. For lettuce, celery, and cabbage, the NoV GII.4 recovery rates were 57.3% ± 6.5%, 52.5% ± 1.7%, and 60.3% ± 3.9%, respectively, using a glycine/NaCl elution buffer (0.25 M glycine/0.14 M NaCl, pH 9.5). The reductions of NoV GII.4 were 3.17, 3.06, and 3.27 log10 genomic copies/μL for lettuce, celery, and cabbage, respectively, at 1000 ppm NaOCl, while a reduction of ∼3 log10 genomic copies/μL was obtained when the samples were treated with a combination of 100 ppm NaOCl and 0.4% SMS pentahydrate. Taken together, these results demonstrated that combined treatment with NaOCl and SMS pentahydrate was an efficient strategy to reduce the concentration of NaOCl for control of NoV GII.4 contamination in fresh vegetables.

Insights in luteovirid structural biology guided by chemical cross-linking and high resolution mass spectrometry

Interactions among plant pathogenic viruses in the family Luteoviridae and their plant hosts and insect vectors are governed by the topology of the viral capsid, which is the sole vehicle for long distance movement of the viral genome. Previous application of a mass spectrometry-compatible cross-linker to preparations of the luteovirid Potato leafroll virus (PLRV; Luteoviridae: Polerovirus) revealed a detailed network of interactions between viral structural proteins and enabled generation of the first cross-linking guided coat protein models. In this study, we extended application of chemical cross-linking technology to the related Turnip yellows virus (TuYV; Luteoviridae: Polerovirus). Remarkably, all cross-links found between sites in the viral coat protein found for TuYV were also found in PLRV. Guided by these data, we present two models for the TuYV coat protein trimer, the basic structural unit of luteovirid virions. Additional cross-links found between the TuYV coat protein and a site in the viral protease domain suggest a possible role for the luteovirid protease in regulating the structural biology of these viruses.

The genome sequence of Brassica campestris chrysovirus 1, a novel putative plant-infecting tripartite chrysovirus

A putative chrysovirus recovered from Brassica campestris var. purpurea and provisionally named "Brassica campestris chrysovirus 1" (BrcCV1) was sequenced. The genome of the putative BrcCV1 consists of three double-stranded RNAs (dsRNAs) comprising 3,639 (dsRNA 1), 3,567 (dsRNA 2) and 3,337 (dsRNA 3) base pairs, respectively, each containing a single open reading frame (ORF 1-3). The putative proteins encoded by ORF 1-3 show homologies to RdRp, CP and chryso-P3 of approved or tentative chrysoviruses. In addition, the three dsRNAs of BrcCV1 contain highly conserved 5' and 3' untranslated regions (UTRs) in a way similar to known chrysoviruses. In a phylogenetic tree based on the conserved amino acid sequences of the RdRps of chrysoviruses, totiviruses and partitiviruses, the putative BrcCV1 formed a separate clade with Raphanus sativus chrysovirus 1 (RasCV1), a putative trisegmented, plant-infecting chrysovirus, in the family Chrysoviridae.

Simultaneous detection and differentiation of three genotypes of Brassica yellows virus by multiplex reverse transcription-polymerase chain reaction

BACKGROUND

Brassica yellows virus (BrYV), proposed to be a new polerovirus species, three distinct genotypes (BrYV-A, BrYV-B and BrYV-C) have been described. This study was to develop a simple, rapid, sensitive, cost-effective method for simultaneous detection and differentiation of three genotypes of BrYV.

RESULTS

In this study, a multiplex reverse transcription-polymerase chain reaction (mRT-PCR) was developed for simultaneous detection and differentiation of the three genotypes of BrYV. The three genotypes of BrYV and Tunip yellows virus (TuYV) could be differentiated simultaneously using six optimized specific oligonucleotide primers, including one universal primer for detecting BrYV, three BrYV genotype-specific primers, and a pair of primers for specific detection of TuYV. Primers were designed from conserved regions of each virus and their specificity was confirmed by sequencing PCR products. The mRT-PCR products were 278 bp for BrYV-A, 674 bp for BrYV-B, 505 bp for BrYV-C, and 205 bp for TuYV. Amplification of three target genotypes was optimized by increasing the PCR annealing temperatures to 62 °C. One to three fragments specific for the virus genotypes were simultaneously amplified from infected samples and identified by their specific molecular sizes in agarose gel electrophoresis. No specific products could be amplified from cDNAs of other viruses which could infect crucifer crops. Detection limits of the plasmids for multiplex PCR were 100 fg for BrYV-A and BrYV-B, 10 pg for BrYV-C, and 1 pg for TuYV, respectively. The mRT-PCR was applied successfully for detection of three BrYV genotypes from field samples collected in China.

CONCLUSIONS

The simple, rapid, sensitive, and cost-effective mRT-PCR was developed successfully for detection and differentiation of the three genotypes of BrYV.

RNA-Seq reveals virus-virus and virus-plant interactions in nature

As research on plant viruses has focused mainly on crop diseases, little is known about these viruses in natural environments. To understand the ecology of viruses in natural systems, comprehensive information on virus-virus and virus-host interactions is required. We applied RNA-Seq to plants from a natural population of Arabidopsis halleri subsp. gemmifera to simultaneously determine the presence/absence of all sequence-reported viruses, identify novel viruses and quantify the host transcriptome. By introducing the criteria of read number and genome coverage, we detected infections by Turnip mosaic virus (TuMV), Cucumber mosaic virus and Brassica yellows virus Active TuMV replication was observed by ultramicroscopy. De novo assembly further identified a novel partitivirus, Arabidopsis halleri partitivirus 1 Interestingly, virus reads reached a maximum level that was equivalent to that of the host's total mRNA, although asymptomatic infection was common. AhgAGO2, a key gene in host defence systems, was upregulated in TuMV-infected plants. Multiple infection was frequent in TuMV-infected leaves, suggesting that TuMV facilitates multiple infection, probably by suppressing host RNA silencing. Revealing hidden plant-virus interactions in nature can enhance our understanding of biological interactions and may have agricultural applications.

Effect of Leaf Surface Chemical Properties on Efficacy of Sanitizer for Rotavirus Inactivation

The use of sanitizers is essential for produce safety. However, little is known about how sanitizer efficacy varies with respect to the chemical surface properties of produce. To answer this question, the disinfection efficacies of an oxidant-based sanitizer and a new surfactant-based sanitizer for porcine rotavirus (PRV) strain OSU were examined. PRV was attached to the leaf surfaces of two kale cultivars with high epicuticular wax contents and one cultivar of endive with a low epicuticular wax content and then treated with each sanitizer. The efficacy of the oxidant-based sanitizer correlated with leaf wax content as evidenced by the 1-log10 PRV disinfection on endive surfaces (low wax content) and 3-log10 disinfection of the cultivars with higher wax contents. In contrast, the surfactant-based sanitizer showed similar PRV disinfection efficacies (up to 3 log10) that were independent of leaf wax content. A statistical difference was observed with the disinfection efficacies of the oxidant-based sanitizer for suspended and attached PRV, while the surfactant-based sanitizer showed similar PRV disinfection efficacies. Significant reductions in the entry and replication of PRV were observed after treatment with either disinfectant. Moreover, the oxidant-based-sanitizer-treated PRV showed sialic acid-specific binding to the host cells, whereas the surfactant-based sanitizer increased the nonspecific binding of PRV to the host cells. These findings suggest that the surface properties of fresh produce may affect the efficacy of virus disinfection, implying that food sanitizers should be carefully selected for the different surface characteristics of fresh produce.

IMPORTANCE

Food sanitizer efficacies are affected by the surface properties of vegetables. This study evaluated the disinfection efficacies of two food sanitizers, an oxidant-based sanitizer and a surfactant-based sanitizer, on porcine rotavirus strain OSU adhering to the leaf epicuticular surfaces of high- and low-wax-content cultivars. The disinfection efficacy of the oxidant-based sanitizer was affected by the surface properties of the vegetables, while the surfactant-based sanitizer was effective for both high- and low-wax leafy vegetable cultivars. This study suggests that the surface properties of vegetables may be an important factor that interacts with disinfection with food sanitizers of rotaviruses adhering to fresh produce.

Isolation and Characterization of a Novel Virulent Phage of Lactobacillus casei ATCC 393

A new virulent phage (Lcb) of Lactobacillus casei ATCC 393 was isolated from Chinese sauerkraut. It was specific to L. casei ATCC 393. Electron micrograph revealed that it had an icosahedral head (60.2 ± 0.8 nm in diameter) and a long tail (251 ± 2.6 nm). It belonged to the Siphoviridae family. The genome of phage Lcb was estimated to be approximately 40 kb and did not contain cohesive ends. One-step growth kinetics of its lytic development revealed latent and burst periods of 75 and 45 min, respectively, with a burst size of 16 PFU per infected cell. The phage was able to survive in a pH range between 4 and 11. However, a treatment of 70 °C for 30 min and 75% ethanol or isopropanol for 20 min was observed to inactivate phage Lcb thoroughly. The presence of both Ca(2+) and Mg(2+) showed a little influence on phage adsorption, but they were indispensable to gain complete lysis and improve plaque formation. The adsorption kinetics were similar on viable or nonviable cells, and high adsorption rates maintained between 10 and 37 °C. The highest adsorption rate was at 30 °C. This study increased the knowledge on phages of L. casei. The characterization of phage Lcb is helpful to establish a basis for adopting effective strategies to control phage attack in industry.

Omics Approach to Identify Factors Involved in Brassica Disease Resistance

Understanding plant's defense mechanisms and their response to biotic stresses is of fundamental meaning for the development of resistant crop varieties and more productive agriculture. The Brassica genus involves a large variety of economically important species and cultivars used as vegetable source, oilseeds, forage and ornamental. Damage caused by pathogens attack affects negatively various aspects of plant growth, development, and crop productivity. Over the last few decades, advances in plant physiology, genetics, and molecular biology have greatly improved our understanding of plant responses to biotic stress conditions. In this regard, various 'omics' technologies enable qualitative and quantitative monitoring of the abundance of various biological molecules in a high-throughput manner, and thus allow determination of their variation between different biological states on a genomic scale. In this review, we have described advances in 'omic' tools (genomics, transcriptomics, proteomics and metabolomics) in the view of conventional and modern approaches being used to elucidate the molecular mechanisms that underlie Brassica disease resistance.

The 'emergence' of turnip mosaic virus was probably a 'gene-for-quasi-gene' event

Turnip mosaic potyvirus is a virus of brassicas that emerged from a lineage of monocotyledon-infecting potyviruses about 1000 years ago. In vivo and in silico studies all indicate that sites, primarily in its protein 3 (P3) and cylindrical inclusion protein (CI) genes, but also its small 6 kDa 2 protein (6K2) and genome-linked viral protein (VPg) genes, control host specificity in a dynamic way. It is most likely that non-unique combinations of transient viral genomic single nucleotide polymorphisms (SNPs), not all of them non-synonymous, allowed the host switch to occur. These SNPs were probably ephemeral and replaced over time by other combinations as the population subsequently diverged within, and adapted to, the brassica host population.

Piperitone-derived saturated lactones: synthesis and aphid behavior-modifying activity

Two racemic and two enantiomeric pairs of new saturated lactones with the p-menthane system were obtained. The lactones were synthesized from racemic and enantiomerically enriched cis- and trans-piperitols, which were obtained from piperitone. The structures of the compounds were confirmed by spectroscopic data. The antifeedant activity of piperitone to Myzus persicae was studied, and the biological consequences of structural modifications of piperitone, that is, lactonization and chiral center configuration, were examined as well. The behavioral responses of M. persicae to piperitone and piperitone-derived saturated lactones were investigated to reveal the biological background of their deterrent activity. Piperitone appeared rather neutral or weakly deterrent to aphids. The introduction of a lactone moiety into a piperitone molecule dramatically changed its biological activity. All piperitone-derived lactones evoked negative aphid responses. However, the deterrent activity of individual compounds varied in potency, the time of expression, and the duration of the effect, depending on the spatial structure of the lactone. Lactones (1R,3S,6R)-3-isopropyl-6-methyl-9-oxabicyclo[4.3.0]nonan-8-one and trans-3-isopropyl-6-methyl-9-oxabicyclo[4.3.0]nonan-8-one showed the broadest ranges and the highest potencies and durabilities of deterrent activity to M. persicae: they acted immediately after application, caused a cessation of probing before aphids reached phloem elements, and decreased the quality of phloem sap.

Turnip mosaic potyvirus probably first spread to Eurasian brassica crops from wild orchids about 1000 years ago

Turnip mosaic potyvirus (TuMV) is probably the most widespread and damaging virus that infects cultivated brassicas worldwide. Previous work has indicated that the virus originated in western Eurasia, with all of its closest relatives being viruses of monocotyledonous plants. Here we report that we have identified a sister lineage of TuMV-like potyviruses (TuMV-OM) from European orchids. The isolates of TuMV-OM form a monophyletic sister lineage to the brassica-infecting TuMVs (TuMV-BIs), and are nested within a clade of monocotyledon-infecting viruses. Extensive host-range tests showed that all of the TuMV-OMs are biologically similar to, but distinct from, TuMV-BIs and do not readily infect brassicas. We conclude that it is more likely that TuMV evolved from a TuMV-OM-like ancestor than the reverse. We did Bayesian coalescent analyses using a combination of novel and published sequence data from four TuMV genes [helper component-proteinase protein (HC-Pro), protein 3(P3), nuclear inclusion b protein (NIb), and coat protein (CP)]. Three genes (HC-Pro, P3, and NIb), but not the CP gene, gave results indicating that the TuMV-BI viruses diverged from TuMV-OMs around 1000 years ago. Only 150 years later, the four lineages of the present global population of TuMV-BIs diverged from one another. These dates are congruent with historical records of the spread of agriculture in Western Europe. From about 1200 years ago, there was a warming of the climate, and agriculture and the human population of the region greatly increased. Farming replaced woodlands, fostering viruses and aphid vectors that could invade the crops, which included several brassica cultivars and weeds. Later, starting 500 years ago, inter-continental maritime trade probably spread the TuMV-BIs to the remainder of the world.

Reference gene selection for qRT-PCR analysis in the sweetpotato whitefly, Bemisia tabaci (Hemiptera: Aleyrodidae)

BACKGROUND

Accurate evaluation of gene expression requires normalization relative to the expression of reliable reference genes. Expression levels of "classical" reference genes can differ, however, across experimental conditions. Although quantitative real-time PCR (qRT-PCR) has been used extensively to decipher gene function in the sweetpotato whitefly Bemisia tabaci, a world-wide pest in many agricultural systems, the stability of its reference genes has rarely been validated.

RESULTS

In this study, 15 candidate reference genes from B. tabaci were evaluated using two Excel-based algorithms geNorm and Normfinder under a diverse set of biotic and abiotic conditions. At least two reference genes were selected to normalize gene expressions in B. tabaci under experimental conditions. Specifically, for biotic conditions including host plant, acquisition of a plant virus, developmental stage, tissue (body region of the adult), and whitefly biotype, ribosomal protein L29 was the most stable reference gene. In contrast, the expression of elongation factor 1 alpha, peptidylprolyl isomerase A, NADH dehydrogenase, succinate dehydrogenase complex subunit A and heat shock protein 40 were consistently stable across various abiotic conditions including photoperiod, temperature, and insecticide susceptibility.

CONCLUSION

Our finding is the first step toward establishing a standardized quantitative real-time PCR procedure following the MIQE (Minimum Information for publication of Quantitative real time PCR Experiments) guideline in an agriculturally important insect pest, and provides a solid foundation for future RNA interference based functional study in B. tabaci.

Application of a simple method using minute particles of amorphous calcium phosphate for recovery of norovirus from cabbage, lettuce, and ham

In this study, the amorphous calcium phosphate (ACP) method developed previously for calicivirus concentration from water was applied for norovirus detection from food. The viral recovery from cabbage, lettuce, or ham (10g of each) was firstly examined in seeding experiments with feline caliciviruses (FCVs). The viruses were concentrated by viral adsorption to ACP particles (0.3g) in the eluent solution (40ml) from foods, collection of the particles by centrifugation, followed by dissolution of the particles with 3.3M citric acid (3ml). In ham, FCV recovery was improved by addition of ascorbic acids into the eluent solution before ACP-particle adsorption. Quantitative real-time reverse transcription-PCR (qRT-PCR) revealed that FCV recoveries were 32-33%, 50-55%, and 37-46% from cabbage, lettuce, and ham, respectively, when seeded with 10(3)-10(4) viruses, and detection limits were estimated ∼10(3) genomic copies in all 3 foods. Subsequently, the ACP-concentration method was evaluated for norovirus (NoV) detection from these 3 foods. The recoveries and detection limit of NoVs determined by qRT-PCR were 12-41% and 10(3) (genomic copies) from cabbage, 30-57% and 10(3) from lettuce, and 20-26% and 10(4) from ham, when seeded with 10(3)-10(5) viruses. This simple method may be suitable for NoV detection from these foods.