Characterization of Left-border Flanking Sequences of T-DNA Integration in Transgenic Rice (Oryza sativa L.) Expressing cry1Ab
To understand the molecular details of T-DNA integration, the left border (LB) sequences and flanking plant DNA of 16 independent T-DNA insertions in transgenic cry1Ab rice were analyzed by an inverse PCR approach. DNA sequencing indicated that five of the 16 fragments (31%) were found to have simple or rearranged tandem repeats of right border sequences in a head to tail fashion. Mirror truncations of LB of the T-DNA, as well as mirror rearrangements, such as point mutations, small deletions and inversions were found in the region close to the LB breakpoints in some inserts. Host plant DNA flanking the T-DNA endpoints were also sequenced. The A+T contents in the plant DNA within 50 bp adjacent to the T-DNA endpoints were between 30–76% (average 52.5%), not different from the average genome value. Despite minor mutations and some rearrangements, it appears that T-DNA, harbouring a synthetic cry1Ab coding sequence of 49% GC (as well as uidA and hph), still carries such a foreign gene into ‘transcriptionally active regions’ of the rice genome, which are 55.8% GC on average as predicted from the rice genome sequence.
Keywordsrice cry1Ab Agrobacterium T-DNA left-border right-border repeat DNA sequence promoter
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