Effect of protein aggregation state on coat protein-mediated protection against tobacco mosaic virus using a transient protoplast assay

Designing a recombinant coat protein to reduce tobacco mosaic virus infection in plants

The Tobacco Mosaic Virus (TMV) is a critical plant virus that can cause a significant drop in crop yield. To understand how recombinant coat-protein impacts the affinity and assembly of TMV's subunits, research is being conducted to assess the effect of recombinant protein on virus resistance. To develop a recombinant coat-protein that can lower TMV infection rates in plants, a design strategy was employed that involves creating defective viral subunits leading to incorrect assembly. This method is similar to using defective puzzle pieces that form incorrect connections resulting in disrupted viral assembly, ultimately affecting the production of mature virus particles. The study investigated the effect of mutations on one side of the Tobacco mosaic virus coat-protein using molecular modeling and dynamics simulation techniques. The simulation showed that the recombinant subunit had lower flexibility (between 0.15 to 0.20 nm) compared to the other subunits (between 0.45 to 0.75 nm), which was attributed to the smaller loop area. The study suggests an effective recombinant coat-protein with the potential to prevent virus infection by disrupting the coat-protein assembly process. This approach can be used to design a plant vaccine against viruses. Developing a recombinant protein can also provide benefits to plants such as protection from pests and enhancement of growth and productivity.

The coat protein of tobacco mosaic virus as an anti-tobacco mosaic virus: a molecular dynamics simulation

The Coat Protein (CP) of the Tobacco Mosaic Virus (TMV) executes an important duty in the protection of virus RNA. The interaction between the virus CP and host plant proteins induces infection in the host and creates dark and light green mosaics on crops, which disturb the growth and function of the plant. The interaction between the virus CP and the modified CP, expressed in transgenic plants, causes Coat Protein-Mediated Resistance (CP-MR), which reduces virus infection in transgenic plants. In this study, a model is suggested for resistance as "stop assembly of CP" in the virus. It is based on the fact that the CP, when mutated, acts as a dead-end in virus assembly. For evaluation of the model, we investigated the effect of four mutants including CBT28I, ABT42W, ABD77R, and ABT89W complexes on plant resistance against TMV infection by molecular dynamics simulation. Previous studies had shown the influence of such mutations on the CP-MR. The MD results of in the present study further confirmed the mentioned effect and demonstrated how the mutations could be the cause of CP-MR. The results are calculated by the RMSD, Rg, H-bond, and g-MMPBSA scripts. The change in binding energy between two chains is consistent with CP-MR such that with increase in binding energy, the affinity between two chains was reduced and the CP-MR increased. Based on this model, it is possible to design mutants with a high level of efficiency.Communicated by Ramaswamy H. Sarma.

Plant pathology and RNAi: a brief history

This article describes the discovery of RNA-activated sequence-specific RNA degradation, a phenomenon now referred to as RNA silencing or RNA interference (RNAi). From 1992 to 1996, a series of articles were published on virus resistant transgenic plants expressing either translatable or nontranslatable versions of the coat protein gene of Tobacco etch virus (TEV). Certain transgenic plant lines were resistant to TEV but not to closely related viruses. In these plants a surprising correlation was observed: Transgenic plant lines with the highest degree of TEV resistance had actively transcribed transgenes but low steady-state levels of transgene RNA. Molecular analysis of these transgenic plants demonstrated the existence of a cellular-based, sequence-specific, posttranscriptional RNA-degradation system that was programmed by the transgene-encoded RNA sequence. This RNA-degradation activity specifically targeted both the transgene RNA and TEV (viral) RNA for degradation and was the first description of RNA-mediated gene silencing.

Coat-protein-mediated resistance to tobacco mosaic virus: discovery mechanisms and exploitation

In 1986 we reported that transgenic plants which accumulate the coat protein of tobacco mosaic virus (TMV) are protected from infection by TMV, and by closely related tobamoviruses. The phenomenon is referred to as coat-protein-mediated resistance (CP-MR), and bears certain similarities to cross protection, a phenomenon described by plant pathologists early in this century. Our studies of CP-MR against TMV have demonstrated that transgenically expressed CP interferes with disassembly of TMV particles in the inoculated transgenic cell. However, there is little resistance to local, cell-to-cell spread of infection. CP-MR involves interaction between the transgenic CP and the CP of the challenge virus, and resistance to TMV is greater than to tobamo viruses that have CP genes more distantly related to the transgene. Using the known coordinates of the three-dimensional structure of TMV we developed mutant forms of CP that have stronger inter-subunit interactions, and confer increased levels of CP-MR compared with wild-type CP. Similarly, it is predicted that understanding the cellular and structural basis of CP-MR will lead to the development of variant CP transgenes that each can confer high levels of resistance against a range of tobamoviruses.

Coat protein-mediated resistance in transgenic plants

This review describes the proposed mechanism(s) of classical virus cross-protection in plants, followed by those suggested for coat protein-mediated resistance (CP-mediated resistance). Although both have common features, cross-protection is thought to be a complex response caused by the replication and expression of the entire viral genome, whereas the resistance conferred by the expression of a virus coat protein gene is more limited. The term genetically engineered cross-protection is frequently used because in many cases the phenotype of resistance mimics that of cross-protection. However, CP-mediated resistance, although a narrow term, more accurately describes the resistance that results from the expression of a virus CP gene in transgenic plants.

Transgenic corn plants expressing MDMV strain B coat protein are resistant to mixed infections of maize dwarf mosaic virus and maize chlorotic mottle virus

The maize dwarf mosaic virus strain B (MDMV-B) coat protein (cp) gene was cloned into a monocot expression cassette and introduced into sweet corn cell suspension cultures via particle bombardment or electroporation. Transformed cells were selected on culture media containing 300 mg/l kanamycin, and plants were regenerated. Cells from all transformed lines expressed the cp gene; and one transgenic line synthesized approximately 100-200 micrograms MDMV-cp per gram fresh weight. Plants regenerated from this line were challenged with a virus inoculum concentration adjusted to produce symptoms in nontransgenic controls at six days post inoculation. In growth chamber studies, the presence of the MDMV-cp provided resistance to inoculations with MDMV-A or MDMV-B and to mixed inoculations of MDMV and maize chlorotic mottle virus.

The TMV movement protein: role of the C-terminal 73 amino acids in subcellular localization and function

The role of the C-terminal one-third of the tobacco mosaic virus (TMV) 30-kDa movement protein (MP) on its subcellular localization and on virus spread was investigated. We have constructed eight cDNAs encoding MPs with variable size deletions from the C-terminal end. Expression of the truncated proteins was verified in recombinant yeast using an antiserum directed to a synthetic peptide corresponding to 21 amino acids near the N-terminal end of the MP. In transgenic tobacco plants, MP from which more than 55 amino acids were deleted no longer accumulated in the cell wall fraction of a cellular extract, where the complete MP accumulates. Dye diffusion studies showed that both unmodified and modified MPs that accumulate in the cell wall fraction are able to alter plasmodesmatal size exclusion limits. Biological function of the modified MPs was tested in the transgenic plants with the TMV thermosensitive mutant Ls1 and a TMV genomic RNA transcript lacking a functional MP. There was a correlation between the cell wall localization of the modified MPs and its ability to potentiate virus spread. The results presented here demonstrate the dispensability of the C-terminal 55 amino acids of the MP in its subcellular localization in tobacco plants and its role in virus movement. Moreover, our results show that a stretch of 19 amino acids (195 to 213) is essential for localization of the MP to the cell wall fraction of plant cells.

Tissue-specific expression of the TMV coat protein in transgenic tobacco plants affects the level of coat protein-mediated virus protection

Transgenic tobacco plants were produced that express a chimeric gene encoding the coat protein (CP) of tobacco mosaic virus (TMV) under the control of the promoter from a ribulose bisphosphate carboxylase small subunit (rbcS) gene. Plant lines expressing comparable levels of CP from the rbcS and cauliflower mosaic virus 35S promoters were compared for resistance to TMV. In whole plant assays the 35S:CP constructs gave higher resistance than the rbcS:CP constructs. On the other hand, leaf mesophyll protoplasts isolated from both plant lines were equally resistant to infection by TMV. This indicated that the difference in resistance between the lines in the whole plant assay reflects differences at the level of short- and/or long-distance spread of TMV. Therefore, we propose that the difference in tissue-specific expression between the 35S and rbcS promoters accounts for greater resistance in the plant lines that express the 35S:CP chimeric genes.

Genetic engineering of plants for virus resistance

Historically, control of plant virus disease has involved numerous strategies which have often been combined to provide effective durable resistance in the field. In recent years, the dramatic advances obtained in plant molecular virology have enhanced our understanding of viral genome organizations and gene functions. Moreover, genetic engineering of plants for virus resistance has recently provided promising additional strategies for control of virus disease. At present, the most promising of these has been the expression of coat-protein coding sequences in plants transformed with a coat protein gene. Other potential methods include the expression of anti-sense viral transcripts in transgenic plants, the application of artificial anti-sense mediated gene regulation to viral systems, and the expression of viral satellite RNAs, RNAs with endoribonuclease activity, antiviral antibody genes, or human interferon genes in plants.