2 T-DNAS CO-TRANSFORMED INTO BRASSICA-NAPUS BY A DOUBLE AGROBACTERIUM-TUMEFACIENS INFECTION ARE MAINLY INTEGRATED AT THE SAME LOCUS

Hypocotyl explants of three Brassica napus varieties were infected with two nopaline type Agrobacterium strains each carrying a distinct disarmed T-DNA containing different selectable markers. Selection was done for only one of the markers, after which the regenerated plants were screened for the presence of the second marker. High co-transformation frequencies of both T-DNA's were obtained (39%-85% of the transformants). Where the two T-DNA's were integrated linked, they were usually present in an inverted orientation relative to each other; in all of the cases observed the two right borders were adjacent. Tandem orientations occurred less frequently. The T-DNA's were mainly integrated as intact copies and deletions did not often occur. The co-transformation system described favors a genetically linked integration of the two T-DNA's (78%), although in a single transformed plant both linked and unlinked copies of both T-DNA's may be present.