Autoxidation Products of the Methanolic Extract of the Leaves of Combretum micranthum Exert Antiviral Activity against Tomato Brown Rugose Fruit Virus (ToBRFV).

Tomato brown rugose fruit virus (ToBRFV) is a new damaging plant virus of great interest from both an economical and research point of view. ToBRFV is transmitted by contact, remains infective for months, and to-date, no resistant cultivars have been developed. Due to the relevance of this virus, new effective, sustainable, and operator-safe antiviral agents are needed. Thus, 4-hydroxybenzoic acid was identified as the main product of the alkaline autoxidation at high temperature of the methanolic extract of the leaves of C. micranthum, known for antiviral activity. The autoxidized extract and 4-hydroxybenzoic acid were assayed in in vitro experiments, in combination with a mechanical inoculation test of tomato plants. Catechinic acid, a common product of rearrangement of catechins in hot alkaline solution, was also tested. Degradation of the viral particles, evidenced by the absence of detectable ToBRFV RNA and the loss of virus infectivity, as a possible consequence of disassembly of the virus coat protein (CP), were shown. Homology modeling was then applied to prepare the protein model of ToBRFV CP, and its structure was optimized. Molecular docking simulation showed the interactions of the two compounds, with the amino acid residues responsible for CP-CP interactions. Catechinic acid showed the best binding energy value in comparison with ribavirin, an anti-tobamovirus agent.

Enhanced Antimicrobial Activity and Low Phytotoxicity of Acoustically Synthesized Large Aspect Ratio Cu-BTC Metal-Organic Frameworks with Exposed Metal Sites.

Metal-organic frameworks (MOFs) have recently been shown to be effective antimicrobial agents, particularly if they comprise pathogenicidal metal ions. Nevertheless, the accessibility of these active metal sites to the pathogen, and hence the MOFs' antimicrobial activity itself, is often poor since the metal nodes are usually embedded deep within its three-dimensional (3D) structure. We show that a unique copper-based (copper(II)-benzene-1,3,5-tricarboxylate) MOF, whose quasi-two-dimensional (quasi-2D) swordlike structure facilitates exposure of the metal ions along its surface, exhibits enhanced antimicrobial properties against three representative plant pathogens: a bacterium (Pseudomonas syringae), a fungus (Fusarium solani), and a virus (Odontoglossum ringspot virus (ORSV)). Such superior antimicrobial activity results in low minimum inhibitory concentrations (MICs)─half that of a commercial pesticide and an eighth of its conventional 3D cubic MOF counterpart (HKUST-1)─and hence low phytotoxicity, which can be attributed to the accessibility of the surface copper sites to the pathogen, thereby facilitating their adhesion and physical contact with the MOF. Additionally, we observed that orchids treated with the quasi-2D MOF showed negligible phytotoxicity and 80% decreased viral load. This work constitutes the first study to demonstrate the antimicrobial properties of this novel MOF against bacterial, fungal, and viral plant pathogens, and the first chemical control of ORSV.

Effectiveness of disinfectants against the spread of tobamoviruses: Tomato brown rugose fruit virus and Cucumber green mottle mosaic virus.

BACKGROUND: Tobamoviruses, including tomato brown rugose fruit virus (ToBRFV) on tomato and pepper, and cucumber green mottle mosaic virus (CGMMV) on cucumber and watermelon, have caused many disease outbreaks around the world in recent years. With seed-borne, mechanical transmission and resistant breaking traits, tobamoviruses pose serious threat to vegetable production worldwide. With the absence of a commercial resistant cultivar, growers are encouraged to take preventative measures to manage those highly contagious viral diseases. However, there is no information available on which disinfectants are effective to deactivate the virus infectivity on contaminated hands, tools and equipment for these emerging tobamoviruses. The purpose of this study was to evaluate a collection of 16 chemical disinfectants for their effectiveness against mechanical transmission of two emerging tobamoviruses, ToBRFV and CGMMV. METHODS: Bioassay was used to evaluate the efficacy of each disinfectant based on virus infectivity remaining in a prepared virus inoculum after three short exposure times (10 s, 30 s and 60 s) to the disinfectant and inoculated mechanically on three respective test plants (ToBRFV on tomato and CGMMV on watermelon). Percent infection of plants was measured through symptom observation on the test plants and the presence of the virus was confirmed through an enzyme-linked immunosorbent assay with appropriate antibodies. Statistical analysis was performed using one-way ANOVA based on data collected from three independent experiments. RESULTS: Through comparative analysis of percent infection of test plants, a similar trend of efficacy among 16 disinfectants was observed between the two pathosystems. Four common disinfectants with broad spectrum activities against two different tobamoviruses were identified. Those effective disinfectants with 90-100% efficacy against both tobamoviruses were 0.5% Lactoferrin, 2% Virocid, and 10% Clorox, plus 2% Virkon against CGMMV and 3% Virkon against ToBRFV. In addition, SP2700 generated a significant effect against CGMMV, but poorly against ToBRFV. CONCLUSION: Identification of common disinfectants against ToBRFV and CGMMV, two emerging tobamoviruses in two different pathosystems suggest their potential broader effects against other tobamoviruses or even other viruses.

Antiphytoviral toxins of Actinidia chinensis root bark (ACRB) extract: laboratory and semi-field trials.

BACKGROUND: Actinidia chinensis Planch, which is distributed only in China, has been used to treat hepatitis and cancer. The objective of the present work was to identify the antiviral active ingredient of A. chinensis root bark (ACRB). RESULTS: Bioassay-guided isolation of the most active fraction, the EtOAc extract, led to the identification of seven compounds, (+)-catechins-7-phytol (1), 5-methoxy-coumarin-7-ß-D-glycosidase (2), (+)-catechins (3), fupenzic acid (4), spathodic acid-28-O-ß-D-glucopyranoside (5), 3-oxo-9, 12-diene-30-oic acid (6), and 3-ß-(2-carboxy benzoyloxy) oleanolic acid (7). Of these, 5-methoxy-coumarin-7-ß-D-glycosidase (2) possessed the highest antiviral activity, followed by spathodic acid-28-O-ß-D-glucopyranoside (5). Thus, compounds 2 and 5 were the main active constituents, with potential for further development as biological antiviral agents. CONCLUSION: The results suggest that ACRB possesses great potential value for development of an antiviral agent to control phytoviral diseases. © 2018 Society of Chemical Industry.

Inhibitory Components from Glycosmis stenocarpa on Pepper Mild Mottle Virus.

The goal of this study was to identify a source of natural plant compounds with inhibitory activity against pepper mild mottle virus (PMMoV). We showed, using a half-leaf assay, that murrayafoline-A (1) and isomahanine (2) isolated from the aerial parts of Glycosmis stenocarpa have inhibitory activity against PMMoV through curative, inactivation, and protection effects. Using a leaf-disk assay, we confirmed that 2 inhibited virus replication in Nicotiana benthamiana. Using electron microscopy, we found that a mixture of the virus with 2 resulted in damage to the rod-shaped virus.

Overexpression of a host factor TOM1 inhibits tomato mosaic virus propagation and suppression of RNA silencing.

A plant integral membrane protein TOM1 is involved in the multiplication of Tomato mosaic virus (ToMV). TOM1 interacts with ToMV replication proteins and has been suggested to tether the replication proteins to the membranes where the viral RNA synthesis takes place. We have previously demonstrated that inactivation of TOM1 results in reduced ToMV multiplication. In the present study, we show that overexpression of TOM1 in tobacco also inhibits ToMV propagation. TOM1 overexpression led to a decreased accumulation of the soluble form of the replication proteins and interfered with the ability of the replication protein to suppress RNA silencing. The reduced accumulation of the soluble replication proteins was also observed in a silencing suppressor-defective ToMV mutant. Based on these results, we propose that RNA silencing suppression is executed by the soluble form of the replication proteins and that efficient ToMV multiplication requires balanced accumulation of the soluble and membrane-bound replication proteins.

The systemic movement of a tobamovirus is inhibited by a cadmium-ion-induced glycine-rich protein.

Systemic movement is central to plant viral infection. Exposure of tobacco plants to low levels of cadmium ions blocks the systemic spread of turnip vein-clearing tobamovirus (TVCV). We identified a tobacco glycine-rich protein, cdiGRP, specifically induced by low concentrations of cadmium and expressed in the cell walls of plant vascular tissues. Constitutive cdiGRP expression inhibited systemic transport of TVCV, whereas suppression of cdiGRP production allowed TVCV movement in the presence of cadmium. cdiGRP exerted its inhibitory effect on TVCV transport by enhancing callose deposits in the vasculature. So cdiGRP may function to control plant viral systemic movement.

Non-toxic concentrations of cadmium inhibit systemic movement of turnip vein clearing virus by a salicylic acid-independent mechanism.

Systemic movement of plant viruses is a central event in viral infection. To better understand this process, the heavy metal cadmium was used to inhibit systemic spread of turnip vein clearing virus (TVCV), a tobamovirus, in tobacco plants. Study of the mechanism by which cadmium exerts this inhibitory effect may provide insights into the essential steps of the TVCV systemic movement pathway. Our results demonstrated that cadmium treatment did not affect TVCV transport from the inoculated non-vascular tissue into the plant vasculature but blocked viral exit into uninoculated non-vascular tissues. Thus, TVCV virions may enter and exit the host plant vascular system by two different mechanisms. We also showed that cadmium-treated plants still supported systemic spread of an unrelated tobacco etch virus (TEV), suggesting multiple pathways for systemic infection. Finally, cadmium-induced arrest in TVCV systemic infection was shown to occur by a salicylic acid-independent mechanism.

Inhibition of plant viral systemic infection by non-toxic concentrations of cadmium.

Heavy metal, such as cadmium, have a significant impact on plant physiology. However, their potential effect on plant-pathogen interaction, an important biological process, has not been examined. This study shows that exposure of tobacco plants to non-toxic concentrations of cadmium completely blocked viral disease caused by turnip vein clearing virus. Cadmium-mediated viral protection was due to inhibition of the systemic movement of the virus, i.e. its spread from the inoculated into uninoculated leaves. Exposure of plants to cadmium had no effect on viral replication, assembly and local movement within the inoculated leaf. Analysis of the viral presence in different tissues suggested that cadmium treatment inhibited virus exit from the vascular tissue into uninoculated leaves rather than its entry into the host plant vasculature. Higher, toxic levels of cadmium did not produce this inhibitory effect on viral movement, allowing the systemic spread of the virus and development of the viral disease. These observations suggest that cadmium-induced viral protection requires a relatively healthy, unpoisoned plant in which non-toxic levels of cadmium may trigger the production of cellular factors which interfere with the viral systemic movement.

Inhibition of a plant virus infection by analogs of melittin.

An approach that enables identification of specific synthetic peptide inhibitors of plant viral infection is reported. Synthetic analogs of melittin that have sequence and structural similarities to an essential domain of tobacco mosaic virus coat protein were found to possess highly specific antiviral activity. This approach involves modification of residues located at positions analogous to those that are critical for virus assembly. The degree of inhibition found correlates well with sequence similarities between the viral capsid protein and the melittin analogs studied as well as with the induced conformational changes that result upon interaction of the peptides and ribonucleic acid.