Benefits of using genomic insulators flanking transgenes to increase expression and avoid positional effects.

For more than 20 years, plant biologists have tried to achieve complete control of transgene expression. Until the techniques to target transgenes to safe harbor sites in the genome become routine, flanking transgenes with genetic insulators, DNA sequences that create independent domains of gene expression, can help avoid positional effects and stabilize their expression. We have, for the first time, compared the effect of three insulator sequences previously described in the literature and one never tested before. Our results indicate that their use increases transgene expression, but only the last one reduces variability between lines and between individuals. We have analyzed the integration of insulator-flanked T-DNAs using whole genome re-sequencing (to our knowledge, also for the first time) and found data suggesting that chiMARs can shelter transgene insertions from neighboring repressive epigenetic states. Finally, we could also observe a loss of accuracy of the RB insertion in the lines harboring insulators, evidenced by a high frequency of truncation of T-DNAs and of insertion of vector backbone that, however, did not affect transgene expression. Our data supports that the effect of each genetic insulator is different and their use in transgenic constructs should depend on the needs of each specific experiment.