Fischer Ute, Kuhlmann Markus, Pecinka Ales, Schmidt Renate, Mette Michael F
Leibniz-Institute of Plant Genetics and Crop Plant Research (IPK), Corrensstrasse 3, 06466 Gatersleben, Germany.
Plant J. 2008 Jan;53(1):1-10. doi: 10.1111/j.1365-313X.2007.03311.x. Epub 2007 Oct 27.
Transcription of a nopaline synthase promoter (pNOS) inverted repeat provides an RNA signal that can trigger transcriptional gene silencing and methylation of pNOS promoters in trans. The degree of silencing is influenced by the local DNA features close to the target promoter integration sites. Among 26 transgenic Arabidopsis thaliana lines harbouring single copies of a T-DNA including a pNOS-NPTII reporter gene at different chromosomal loci, NPTII RNA levels showed limited variation. When challenged by the silencer transgene providing the pNOS RNA signal, reduction of the NPTII RNA levels in the F(1) generation varied by more than 100-fold, ranging from no reduction to reduction to <1% of the non-silenced level. Silencing was generally correlated with proportional DNA methylation in the pNOS region, except for one target transgene showing substantial DNA methylation without adequate silencing. Silencing was progressive through generations. Differences in the degree of silencing among the target transgenes were transmitted at least to the F(3) generation, and seemed to be influenced by transgene-flanking sequences. Apparently, close-by repeats promoted, whereas close-by functional genes diminished, the response to the silencing signal.
胭脂碱合成酶启动子（pNOS）反向重复序列的转录产生一种RNA信号，该信号可在反式作用中触发转录基因沉默以及pNOS启动子的甲基化。沉默程度受靠近靶启动子整合位点的局部DNA特征影响。在26个携带包含pNOS-NPTII报告基因的T-DNA单拷贝且位于不同染色体位点的转基因拟南芥株系中，NPTII RNA水平显示出有限的变化。当受到提供pNOS RNA信号的沉默转基因挑战时，F(1)代中NPTII RNA水平的降低幅度超过100倍，范围从无降低到降低至非沉默水平的<1%。除了一个靶转基因显示出大量DNA甲基化但没有足够的沉默外，沉默通常与pNOS区域中按比例的DNA甲基化相关。沉默在世代间是渐进的。靶转基因之间沉默程度的差异至少传递到F(3)代，并且似乎受转基因侧翼序列的影响。显然，附近的重复序列促进了对沉默信号的响应，而附近的功能基因则减弱了这种响应。
