Tobacco mosaic virus movement protein complements a Potato spindle tuber viroid RNA mutant impaired for mesophyll entry but not mutants unable to enter the phloem.

Tobacco mosaic virus movement protein (TMV MP) is essential for virus spread between cells. To accomplish its task, TMV MP binds viral RNA, interacts with components of the cytoskeleton, and increases the size exclusion limit (SEL) of plasmodesmata. Plasmodesmata are gated intercellular channels that allow passage of small molecules and macromolecules, including RNA and protein, between plant cells. Moreover, plasmodesmata are diverse and those connecting different cell types appear to have unique mechanisms to regulate macromolecular trafficking, which likely contributes to the establishment of distinct cell boundaries. Consequently, TMV MP might be competent to mediate RNA transport through some but not all plasmodesmal gates. Due to a lack of viral mutants defective for movement between specific cell types, the ability of TMV MP in this regard is incompletely understood. In contrast, a number of trafficking impaired Potato spindle tuber viroid (PSTVd) mutants have been identified. PSTVd is a systemically infectious non-coding RNA that nevertheless can perform all functions required for replication as well as cell-to-cell and systemic spread. Previous studies have shown that PSTVd employs different structure and sequence elements to move between diverse cell types in host plants, and mutants defective for transport between specific cell types have been identified. Therefore, PSTVd may serve as a tool to analyze the functions of MPs of viral and cellular origin. To probe the RNA transport activity of TMV MP, transgenic plants expressing the protein were inoculated with PSTVd mutants. Remarkably, TMV MP complemented a PSTVd mutant defective for mesophyll entry but could not support two mutants impaired for phloem entry, suggesting it fails to productively interface with plasmodesmata at the phloem boundary and that additional viral and host factors may be required. Consistent with this idea, TMV co-infection, but not the combination of MP and coat protein (CP) expression, was able to complement one of the phloem entry mutants. These observations suggest that phloem loading is a critical impediment to establishing systemic infection that could involve the entire ensemble of TMV proteins. They also demonstrate a novel strategy for analysis of MPs.

Possible mechanism of action of antiviral proteins from the leaves of Chenopodium album L.

Antiviral proteins (AVPs) named CAP-I and CAP-II purified from the leaves of Chenopodium album cv Pusa Bathua-1 induced systemic resistance against tobacco mosaic virus (TMV) and sunnhemp rosette virus (SRV) in both hypersensitive as well as systemic hosts. An increased accumulation of two polypeptides (approximately 17 kDa and approximately 26 kDa) was observed in untreated upper leaves of Cyamopsis tetragonoloba plants whose basal leaves were treated with CAP-I/CAP-II. Both AVPs exhibited ribosomal RNA N-glycosidase activity on 28S rRNA of tobacco leaves and also caused in vitro degradation of TMV RNA. It is suggested that the CAP-I and -II are multi-functional and may be acting at multiple levels to ensure maximum possible inhibition of viral infection.

Effects of homeopathic arsenic on tobacco plant resistance to tobacco mosaic virus. Theoretical suggestions about system variability, based on a large experimental data set.

CONTEXT: This research aimed at verifying the efficacy of homeopathic treatments by plant-based bioassays, which may be suitable for basic research, because they lack placebo effects and provide large datasets for statistical analyses. OBJECTIVE: To evaluate the effects of homeopathic treatments of arsenic trioxide (As2O3) on tobacco plants subjected to tobacco mosaic virus (TMV) inoculation as biotic stress. DESIGN: Blind, randomized experiment using tobacco leaf disks. MATERIALS AND METHODS: Tobacco plants (Nicotiana tabacum L. cultivar Samsun) carrying the TMV resistance gene N. TMV inoculated leaf disks were floated for 3 days in the following: Distilled water (control). H2O 5 and 45 decimal and centesimal potencies. As2O3 5 and 45 decimal and centesimal potencies. The main outcome measures is the number of hypersensitive lesions observed in a leaf disk. RESULTS: Homeopathic treatments of arsenic induce two effects on the plant: (i) increased resistance to TMV; (ii) decrease variability between experiments (system variability). CONCLUSIONS: In this experimental model two actions of homeopathic treatment were detected: decrease in system variability and enhancement of the natural tendency of the system towards an 'equilibrium point'.

Site-specific cleavage of tobacco mosaic virus RNA: a study of factors influencing the cleavage.

DNA oligomer directed ribonuclease H (RNase H) methodology is applied to specifically cleave tobacco mosaic virus (TMV) RNA. Using a synthetic DNA oligomer P(dT8)dCdC, complementary to a region from nucleotide 5545 to nucleotide 5554 at the 3' end of TMV RNA, we have cleaved the RNA at the site of polynucleotides complementary to the DNA oligomer. Factors such as secondary structure of the RNA, concentrations of DNA oligomer, RNase H and magnesium ions in the reaction mixture, and time of incubation were optimized for the RNase H cleavage of TMV RNA-DNA oligomer complex. Denaturation of TMV RNA with 50% dimethyl sulphoxide at 50 degrees C is essential for the site-specific cleavage.