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首页> 外文期刊>Genetics: A Periodical Record of Investigations Bearing on Heredity and Variation >TnpA trans-activates methylated maize Suppressor-mutator transposable elements in transgenic tobacco.
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TnpA trans-activates methylated maize Suppressor-mutator transposable elements in transgenic tobacco.

机译：TnpA反式激活转基因烟草中的甲基化玉米抑制子-突变子转座因子。

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The maize Suppressor-mutator (Spm) transposable element is subject to epigenetic inactivation in transgenic tobacco, as it is in maize. Spm inactivation in tobacco is correlated with increased methylation of sequences near the element's transcription start site. To determine whether element-encoded gene products can promote the reactivation of an inactive element, we investigated the effects of introducing individual CaMV 35S promoter-driven cDNAs for tnpA, tnpB, tnpC and tnpD, the element's four known protein-coding sequences. Introduction of the tnpA cDNA promoted the reactivation of the inactive resident Spm element, as judged by the appearance of regenerants with very early excision events and transposed elements. By contrast, the tnpB, tnpC and tnpD cDNAs had no affect on the activity of the resident Spm element. Similar results were obtained when the element-encoded cDNAs were introduced either by Agrobacterium-mediated retransformation or by a genetic cross. Reactivation of an inactive Spm by the tnpA cDNA is accompanied by reduced methylation of several methylation-sensitive restriction sites near the element's transcription start site. Maintenance of the reactivated Spm element in an active state requires the continued presence of the tnpA cDNA. Elimination of the tnpA cDNA locus by genetic segregation generally results in decreased element activity, as judged by a low frequency of excision events, and is accompanied by increased methylation of the element's 5'-end. Exceptions resembling the phenomenon of "presetting" are also observed in which progeny plants that did not receive the tnpA cDNA locus after meiotic segregation maintain high excision activity and exhibit low methylation levels.
机译：玉米抑制子-突变体（Spm）转座因子在玉米中和在转基因烟草中一样都遭受表观遗传失活。烟草中的Spm失活与元件转录起始位点附近序列的甲基化增加有关。为了确定元素编码的基因产物是否可以促进失活元件的重新激活，我们研究了为该元素的四个已知蛋白编码序列tnpA，tnpB，tnpC和tnpD引入单独的CaMV 35S启动子驱动的cDNA的作用。 tnpA cDNA的引入促进了失活的常驻Spm元件的重新激活，这可以通过具有非常早期切除事件和转座元件的再生子的出现来判断。相反，tnpB，tnpC和tnpD cDNA对驻留的Spm元件的活性没有影响。当通过农杆菌介导的再转化或通过遗传杂交引入元件编码的cDNA时，获得了相似的结果。通过tnpA cDNA重新激活无活性的Spm时，伴随着该元件转录起始位点附近几个甲基化敏感的限制性位点的甲基化降低。将重新激活的Spm元件维持在活性状态需要tnpA cDNA的持续存在。通过基因分离消除tnpA cDNA基因座通常导致元件活性降低，这由切除事件的频率较低来判断，并伴有该元件5'-末端甲基化的增加。还观察到类似于“预设”现象的例外，其中在减数分裂分离后未接受tnpA cDNA基因座的后代植物保持较高的切除活性并表现出较低的甲基化水平。

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