Abstract
Transgenes introduced into the plant genome can be silenced. Plant transformation methods do not allow the introduction of a defined number of transgenes into the genome, so the number of inserted copies, their chromosomal position, and their local arrangement vary between transformants. In order to address how increased copy number affects expression of the transgene, we used intercrosses of transgenic Arabidopsis plants containing a single copy of a transgene. We analyzed 72 progeny derived from a hemizygous plant containing the transgene at four different chromosomal loci. When one to five copies of the transgene are present in the genome, a positive correlation between transgene copy number and expression is observed, whereas six, seven, and eight copies of the transgene result in gene silencing. The silencing is reversible during meiosis, and transgenes are epigenetically silenced. DNA methylation and siRNA from the transgenes is correlated with gene silencing.
