Expression of an antisense viral gene in transgenic tobacco confers resistance to the DNA virus tomato golden mosaic virus.

Transgenic tobacco plants carrying a genetic cassette including an antisense DNA sequence of the virally encoded AL1 gene of the geminivirus tomato golden mosaic virus (TGMV) were constructed; AL1 encodes a protein absolutely required for TGMV DNA replication. These genetic cassettes also contained, on the same transcription unit, a gene encoding hygromycin resistance, which allowed selection for concomitant expression of the antisense gene. In transgenic lines, RNA transcripts of the predicted size and strand specificity were detected in antisense plants and sense controls. After infection of plants with TGMV, by agroinoculation, the frequency of symptom development was very significantly reduced in a number of antisense lines and correlated, broadly, with the abundance of antisense RNA transcript and with a reduction in viral DNA harvested from infected leaf tissue. We used an in vitro assay to study viral DNA replication in the absence of cell-to-cell spread; no replication was seen in five of the six antisense lines studied, in contrast to controls.