ABSTRACT

Levels of transgene expression in plants are generally unpredictable and vary between independent transformants. This variability is the result of a number of factors, including transgene rearrangement, homology-based co-suppression, transgene copy number or the transgene integration site (position effect). There is mounting evidence that among other regulatory sequences and DNA elements, flanking repetitive sequences may enhance the frequency of transformation and gene expression by `overcoming` the negative position effect. Such elements are referred to as matrix attachment regions (MARs) or scaffold attachment regions (SARs). MARs are typically AT-rich sequences, and have been shown to enhance the stability of transgene expression, or, in other cases, actually up-regulate transgene expression. Experimental results demonstrate that heterologous MAR sequences from other plant species, or, indeed, from animal genomes, can be effective in a range of plants.

In this review we examine the evidence published to date to support the theory that MARs enhance expression of various heterologous reporter genes in plant systems when integrated into the genome.