T-DNA INTEGRATION PATTERNS IN CO-TRANSFORMED PLANT-CELLS SUGGEST THATT-DNA REPEATS ORIGINATE FROM COINTEGRATION OF SEPARATE T-DNAS

Nicotiana protoplasts and Arabidopsis leaf discs or roots were co-cult ivated with two Agrobacterium strains each carrying a different T-DNA. Go-transformed plants were selected and the integration of the differ ent T-DNAs was analysed at the genetic and genomic level. Genetic anal ysis showed that the T-DNAs derived from different bacteria were frequ ently integrated at the same locus, independent of the plant species o r transformation method used. Southern analysis revealed that 12 out o f 27 Arabidopsis transformants contained the co-transferred T-DNAs lin ked to each other in all possible configurations but with a preference for those with at least one right border involved in linkage. Overall , our data support the hypothesis that ligation of separate T-DNAs is a dominant mechanism in formation of the frequently observed repeats o f identical T-DNAs. We propose a scheme which could explain the format ion of T-DNA repeats and the preferential involvement of right borders in T-DNA linkages.