HOMOLOGY-DEPENDENT GENE SILENCING IN TRANSGENIC PLANTS - EPISTATIC SILENCING LOCI CONTAIN MULTIPLE COPIES OF METHYLATED TRANSGENES
HOMOLOGY-DEPENDENT GENE SILENCING IN TRANSGENIC PLANTS - EPISTATIC SILENCING LOCI CONTAIN MULTIPLE COPIES OF METHYLATED TRANSGENES
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DOI：
10.1007/bf00285449
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发表时间：
1994-08-02
期刊：
影响因子：
--
通讯作者：
MATZKE, MA
中科院分区：
文献类型：
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作者：
MATZKE, AJM;NEUHUBER, F;MATZKE, MA
先前的工作表明，两个同源、不连锁的转基因位点可以在植物细胞核中相互作用，导致一个位点上基因的非相互反式失活和甲基化。在这里，我们报告了不同转基因位点的结构和甲基化，这些转基因位点包含相同的构建体，但能够不同程度地失活和甲基化部分同源的、未连锁的靶位点。沉默基因座包含转基因构建体的多个甲基化拷贝，而非沉默基因座包含单个未甲基化拷贝。通过产生强沉默基因座的新等位基因，进一步证明了沉默活性强度与拷贝数/甲基化程度之间的对应关系：减少该沉默基因座内的转基因拷贝数和甲基化降低了其灭活靶基因座的能力。强沉默位点位于端粒附近，可以使原始目标构建体的各种结构变体反式失活，无论它们在基因组中的位置如何。这表明沉默位点可以扫描整个基因组中的同源区域，这一过程可能受到其端粒位置的帮助。我们的数据支持这样的观点，即植物中未连锁的同源转基因的上位性反式失活是由于转基因位点之间预先存在的表观遗传差异造成的，随后通过涉及DNA-DNA配对的“表观基因转换”来平衡这种差异。
Previous work has shown that two homologous, unlinked transgene loci can interact in plant nuclei, leading to non-reciprocal trans-inactivation and methylation of genes at one locus. Here, we report the structure and methylation of different transgene loci that contain the same construct but are variably able to inactivate and methylate a partially homologous, unlinked target locus. Silencing loci comprised multiple, methylated copies of the transgene construct, whereas a non-silencing locus contained a single, unmethylated copy. The correspondence between strength of silencing activity and copy number/degree of methylation was further demonstrated by producing novel alleles of a strong silencing locus: reducing the transgene copy number and methylation within this silencing locus decreased its ability to inactivate the target locus. The strong silencing locus, which was located close to a telomere, trans-inactivated various structural variants of the original target construct, regardless of their location in the genome. This suggests that the silencing locus can scan the entire genome for homologous regions, a process possibly aided by its telomeric location. Our data support the idea that epistatic trans-inactivation of unlinked, homologous transgenes in plants results from a pre-existing epigenetic difference between transgene loci, which is subsequently equalized by ''epigene conversion'' involving DNA-DNA pairing.