TRANSGENIC DNA INTEGRATED INTO THE OAT GENOME IS FREQUENTLY INTERSPERSED BY HOST DNA

Integration of transgenic DNA into the plant genome was investigated i n 13 transgenic oat (Avena sativa L.) lines produced using microprojec tile bombardment with one or two cotransformed plasmids, In all transf ormation events, the transgenic DNA integrated into the plant genome c onsisted of intact transgene copies that were accompanied by multiple, rearranged, and/or truncated transgene fragments,All fragments of tra nsgenic DNA cosegregated, indicating that they were integrated at sing le gene loci. Analysis of the structure of the transgenic loci indicat ed that the transgenic DNA was interspersed by the host genomic DNA. T he number of insertions of transgenic DNA within the transgene loci va ried from 2 to 12 among the 13 lines. Restriction endonucleases that d o not cleave the introduced plasmids produced restriction fragments ra nging from 3.6 to about 60 kb in length hybridizing to a probe compris ing the introduced plasmids, Although the size of the interspersing ho st DNA within the transgene locus is unknown, the sizes of the transge ne-hybridizing restriction fragments indicated that the entire transge ne locus must be at least from 35-280 kb, The observation that all tra nsgenic lines analyzed exhibited genomic interspersion of multiple clu stered transgenes suggests a predominating integration mechanism. We p ropose that transgene integration at multiple clustered DNA replicatio n forks could account for the observed interspersion of transgenic DNA with host genomic DNA within transgenic loci.