Insertion in the coding region of the movement protein improves stability of the plasmid encoding a tomato mosaic virus-based expression vector

A major obstacle in the genetic manipulation of tomato mosaic virus (ToMV) is the instability of the plasmid containing the infectious full-length cDNA of the ToMV vector, which often prevents the subcloning of a foreign gene of interest into the vector. We found that an insertion of a 0.3-1.6-kbp DNA fragment in the movement protein (MP) coding region effectively attenuated bacterial toxicity of the plasmid and greatly increased plasmid yield. Accumulation of a modified ToMV containing a 0.3-kb insertion in the MP coding region was comparable to that of a modified ToMV without an insertion in tobacco BY-2 protoplasts, while an insertion more than 0.6 kb significantly reduced accumulation of the viral RNA. The modified ToMV vector containing a 0.3-kb insertion was easily manipulated to introduce a coding sequence for human interferon-gamma (HuIFN-gamma) and successfully utilized to produce HuIFN-gamma in both BY-2 protoplasts and transgenic BY-2 cells.