Expression of randomly integrated single complete copy transgenes does not vary in Arabidopsis thaliana

The high variability of transgene expression is frequently observed in independent transgenic lines. Variability of transgene expression has been attributed to several factors, including differences in chromosome position, repeat sequences and copy number. The eukaryotic genome, with a heterogeneous chromatin structure, is not homogeneous for transcriptional activity. Chromatin structure at the site of integration can affect transgene expression; this phenomenon is called the position effect. In this study, we investigated whether position effects confer variability of transgene expression in Arabidopsis thaliana. We analyzed the expression of randomly integrated single 'complete' (intact, non-truncated, non-rearranged) copy transgenes in A. thaliana. Ten independent lines containing single complete copies of the transgene located at different chromosome positions showed very similar levels of transgene expression, and variability of transgene expression was not observed. This result indicates that position effects may not generally be a major cause of variability of transgene expression in A. thaliana.