Historical overview of research on the tobacco mosaic virus genome: genomeorganization, infectivity and gene manipulation

Early in the development of molecular biology TMV RNA was widely used as a mitochondrial RNA that could be purified easily, and it contributed much to research on protein synthesis. Also, in the early stages of elucidation of the genetic code, artificially produced TMV mutants were widely used and p rovided the first proof that the genetic code was non-overlapping. In 1982, Goelet et al. determined the complete TR IV RNA base sequence of 6395 nucl eotides. The four genes (130K, 180K, 30K and coat protein) could then be ma pped at precise locations in the TMV genome. Furthermore it had become clea r, a little earlier, that genes located internally in the genome were expre ssed via subgenomic mRNAs. The initiation site for assembly of TMV particle s was also determined. However, although TMV contributed so much at the beginning of the developme nt of molecular biology, its influence was replaced by that of Escherichia coli and its phages in the next phase. As recombinant DNA technology develo ped in the 1980s, RNA virus research became more detached from the frontier of molecular biology To recover from this setback, a gene-manipulation sys tem was needed for RNA viruses. In 1986, two such systems were developed fo r TMV, using full-length cDNA clones, by Dawson's group and by Okada's grou p. Thus, reverse genetics could be used to elucidate the basic functions of all proteins encoded by the TMV genome. Identification of the function of the 30K protein was especially important because it was the first evidence that a plant virus possesses a cell-to-cell movement function, Many other p lant viruses have since been found to encode comparable 'movement proteins' . TMV thus became the first plant virus for which structures and functions were known for all its genes. At the birth of molecular plant pathology, TM V became a leader again. TMV has also played pioneering roles in many other fields. TMV was the firs t virus for which the amino acid sequence of the coat protein was determine d and first virus for which cotranslational disassembly was demonstrated bo th in vivo and in vitro. It was the first virus for which activation of a r esistance gene in a host plant was related to the molecular specificity of a product of a viral gene. Also, in the field of plant biotechnology, TMV v ectors are among the most promising. Thus, for the 100 years since Beijerin ck's work, TMV research has consistently played a leading role in opening u p new areas of study, not only in plant pathology, but also in virology bio chemistry, molecular biology, RNA genetics and biotechnology.