Expression of a bacterial gene in plants by using a viral vector

Abstract

Several properties of the cauliflower mosaic virus (CaMV) indicate that it could provide a useful vector for gene transfer in higher plants: (1) it has a relatively small double-stranded genome that can be easily manipulated in vitro1–3; (2) cloned viral DNA is infectious when rubbed onto healthy leaves4,5; (3) virus spreads throughout the plant and can be found in most cells at high copy number. Two regions of the CaMV genome—open reading frames (ORFs) II and VII—do not seem to be essential for infection, as both can be either deleted or expanded by small inserts of foreign DNA6–8. No functional genes have yet been introduced into these ORFs. Here we report the replacement of CaMV ORF II by the R67 plasmid-encoded dihydrofolate reductase (DHFR) gene; this gene (dhfr) confers resistance to methotrexate in Escherichia coli. The chimaeric viral DNA can be stably propagated in turnip plants and the dhfr gene is expressed, producing a functional enzyme.