Homology-dependent gene silencing in transgenic plants: epistatic silencing loci contain multiple copies of methylated transgenes
1994
Matzke, A.J.M. (Austrian Academy of Sciences, Salzburg (Austria). Inst. of Molecular Biology) | Neuhuber, F. | Park, Y.D. | Ambros, P.F. | Matzke, M.A.
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, the structure and methylation of different transgene loci is reported 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. These 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
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