Matrix attachment regions increase transgene expression levels and stability in transgenic rice plants and their progeny

To investigate the effect of matrix attachment regions (MARs) on transgene expression levels and stability in cereal crops, we generated 83 independen t transgenic rice callus lines containing a gusA expression cassette either as a simple expression unit, or flanked with MARs from tobacco (Rb7) or ye ast (ARS1). Transgenic rice plants were regenerated from these callus lines and analysed at the structural and expression levels over two generations. In the first generation (T-0), both Rb7 and ARS1 MARs significantly increa sed transgene expression levels. In the populations of plants containing MA Rs, we observed a significant reduction in the number of non-expressing lin es compared to the population of plants without MARs. However, variation in beta-glucuronidase (GUS) expression levels between independent lines was s imilar both in the presence and absence of flanking MARs. In the presence o f MARs, GUS activity increased in proportion to transgene copy number up to 20 copies, but was generally reduced in lines carrying a higher copy numbe r. In the population of plants without MARs, there was no correlation betwe en expression revel and transgene copy number. In the second generation (T- 1), transgene expression levels were significantly correlated with those of the T-0 parents. The Rb7 MARs significantly improved the stability of tran sgene expression levels over two generations, and therefore appear to offer protection against transgene silencing. Our study shows that the exploitat ion of MARs may be an important strategy for stabilising transgene expressi on revels in genetically engineered cereals.