Transgenic rice as a system to study the stability of transgene expression: multiple heterologous transgenes show similar behaviour in diverse genetic backgrounds

The success of contemporary breeding programmes involving genetic engineeri ng depends on the stability of transgene expression over many generations. We studied the stability of transgene expression in 40 independent rice pla nt lines representing ii diverse cultivated varieties. Each line contained three or four different transgenes delivered by particle bombardment, eithe r by cotransformation or in the form of a cointegrate vector. Approximately 75% of the lines (29/40) demonstrated Mendelian inheritance of all transge nes, suggesting integration at a single locus. We found that levels of tran sgene expression varied among different lines, but primary transformants sh owing high-level expression of the gna, gusA, hpt and bar transgenes faithf ully transmitted these traits to progeny. Furthermore, we found that cry1Ac and cry2A transgene expression was stably inherited when primary transform ants showed moderate or low-level expression. Our results show that six tra nsgenes (three markers and three insect-resistance genes) were stably expre ssed over four generations of transgenic rice plants. We showed that transg ene expression was stable in lines of all the rice genotypes we analysed. O ur data represent a step forward in the transfer of rice genetic engineerin g technology from model varieties to elite breeding lines grown in differen t parts of the world.