FLANK MATRIX ATTACHMENT REGIONS (MARS) FROM CHICKEN, BEAN, YEAST OR TOBACCO DO NOT PREVENT HOMOLOGY-DEPENDENT TRANS-SILENCING IN TRANSGENICTOBACCO PLANTS

The effect of flanking matrix attachment regions (MARs) on homology-de pendent trans-silencing was tested using two strong tuans-silencing lo ci. The transgenic tobacco line 271 carries at a single locus a p35S-R iN-tNos transgene which is able to silence, in trans and at the transc riptional level, the expression of any p35S-driven transgene irrespect ive of its position. The transgenic tobacco line 6b8 carries at a sing le locus a p35S-uidA-tRbcS transgene which is able to silence in tl ws , at the post-transcriptional level, the expression of any uidA-expres sing transgene irrespective of its position. Various transgenic tobacc o lines carrying a target p35S-uidA-tNos transgene, flanked on each si de by MARs from chicken, bean, yeast or tobacco, were crossed with lin es carrying the 271 and 6b8 loci. Expression of the target transgene w as silenced in all hybrids, irrespective of the presence or absence of MAR sequences. These results therefore demonstrate that MARs are not able to protect transgene expression from strong silencing loci that a ct in trans.