Efficient targeting of foreign genes into the tobacco plastid genome.

The pPRV plasmids are vectors for targeted insertion of foreign genes into the tobacco plastid genome (ptDNA). The vectors are based on the pUC119 plasmid which replicates in E. coli but not in plastids. The spectinomycin resistance (aadA) gene and a multiple cloning site (MCS) are flanked by 1.8-kb and 1.2-kb ptDNA sequences. Biolistic delivery of vector DNA, followed by spectinomycin selection, yields plastid transformants at a reproducible frequency, approximately 1 transplastomic line per bombarded sample. The selected aadA gene and linked non-selectable genes cloned into the MCS are incorporated into the ptDNA by two homologous recombination events via the flanking ptDNA sequences. The transplastomes thus generated are stable, and are maternally transmitted to the seed progeny. The pPRV vector series targets insertions between the divergently transcribed trnV gene and the rps12/7 operon. The lack of readthrough transcription of appropriately oriented transgenes makes the vectors an ideal choice for the study of transgene promoter activity.