Transgene organisation in potato after particle bombardment-mediated (co-)transformation using plasmids and gene cassettes

Protocols for efficient co-transformation of potato internodes with genes contained in separate plasmids or gene cassettes (i.e., linear PCR fragments comprising a promoter-gene-terminator) using particle bombardment were established. Twenty-eight out of 62 (45%) and 11 out of 65 (17%) plants transformed with a plasmid containing the selectable marker contained one and two additional non-selected genes, respectively. When gene cassettes were used in transformation, six out of eight plants were co-transformed. Expression analysis showed that 75-80% of the plants transformed with two transgenes expressed both of them, irrespective of the use of plasmids or gene cassettes. Thirty-eight plants containing the gusA reporter-gene and the nptII selectable-marker have been characterised with respect to the molecular organisation of the donor DNAs. Seventeen out of 49 (35%) gusA sites of integration contained one copy of the gene. Only 11 gusA sites (22%) were linked to the site of integration of the selectable marker. When one site of integration contained several copies of the transgene, a predominance of 3'-3' inverted re-arrangement repeats was observed.