Submitted to: Genes and Development
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/14/2000
Publication Date: 11/15/2000
Citation: Interpretive Summary: This work tested two hypotheses: 1) whether site-specific integration of a transgene into a defined chromosome target would result in a reproducible level of gene expression, and 2) whether different integration sites would confer a different expression level on the introduced transgene. The data supported both hypotheses. However, an unexpected finding was that regardless of the site of integration, half of the transgene insertions experience various degrees of transcriptional gene silencing. This silencing phenomenon is associated with new DNA methylation patterns found only on the newly introduced transgenic DNA.
Technical Abstract: In an effort to control the variability of transgene expression in plants, we used Cre-lox mediated recombination to insert a gus reporter gene precisely and reproducibly into different target loci. Each integrant line chosen for analysis harbors a single-copy of the transgene at the designated target site. At any given target site, nearly half of the insertions give a full spatial pattern of transgene expression. The absolute level of expression, however, showed target site-dependency that varied up to ten fold. This substantiates the view that the chromosome position can affect the level of gene expression. An unexpected finding was that nearly half of the insertions at any given target site failed to give a full spatial pattern of transgene expression. These partial patterns of expression appear to be due to gene silencing, as low gus expression correlates with DNA methylation and low transcription. The methylation is specific for the newly integrated DNA. Methylation changes are not found outside of the newly inserted DNA. Both the full and the partial expression states are meiotically heritable. The silencing of the introduced transgenes may be a stochastic event that occurs during transformation.