Tobacco Mosaic Virus Vector And Its Expression Of Exogenous Peptides In Plants

Tobacco mosaic virus (TMV) is a rod-shaped plant virus with a single,positive-sense RNA genome of 6395 nucleotides. One of its separate 3'coterminal subgenomic mRNAs encodes the 17.5 kDa coat protein (CP) of 158amino acids that accumulates to high levels in many host plants. It isassembled by viral coat protein (CP) into rod-shaped virions of about 300nm×15nm.Generally, while a small foreign peptide is inserted after Ser154of the TMV CP, the recombinant TMV can still be assembled into rod-shapedvirus and replicated with high efficiency in host plants. In this paper,the relationship between characteristics of the foreign peptides fused toCP and CP expression, infectivity, morphology and stability of therecombinant viruses was studied using TMV-based vector in tobacco plants.By studying the recombinant viruses (TMVF18TAA and TMVF26TGA)containing a FMDV epitope (F18 and F26, respectively), the effect offoreign peptides containing a Cys residue on CP expression and morphologyof the recombinant TMV virions was studied. Western blot analyses detectednot only the CP fusion but also a high molecular weight CP-specificprotein band (hCP) from the viruses-systematically infected leaves andfrom the purified virus particles in vitro. The irregular shapes anddistorted central channels of TMVF18TAA and TMVF26TGA particles in thenewly infected young leaves were observed using transmission electronmicroscope. Subsequent Cys mutation analyses indicated that these changeswere caused by the Cys residue in the foreign peptide. So the relativitybetween foreign peptide composition, hCP formation and morphologicalchanges of the recombinant TMV particles was established. Moreover, theCys in the foreign peptide can influence foreign peptide expressionefficacy and infectivity of the recombinant TMVs in tobacco plants, amongwhich TMVF18CYTAA and TMVF18CGTAA with the highest.The biophysical properties of the tobacco mosaic tobamovirus (TMV)coat protein (CP) made it possible to display foreign peptides on thesurface of TMV. Many factors impact on symptoms, infectivity and stabilityof recombinant TMV in tobacco plants. These factors include charge andisoelectric point of the CP fusion, inserted sites of foreign peptide inTMV CP and its C-terminal partial amino acid deletion, hydrophilicity ofhybrid CP, composition and length of the foreign peptide and so on. Theseresults are important supplements to the viewpoint indicated by Bendahmaneet al(1999), that is, the pI of the epitope had apparent effect on thehybrid CP pI:charge value for successful epitope display as well as thelack of tolerance to positively charged epitopes on the surface of TMV. Sowe propose that different TMV vectors are suitable for expressingdifferent foreign peptides.