Abstract
BackgroundMeiotically heritable epimutations affecting transgene expression are not well understood, even and in particular in the plant model species, Arabidopsis thaliana. The Arabidopsis trans-silencer locus, C73, which encodes a fusion protein between the repressor of photomorphogenesis, COP1, and green fluorescent protein (GFP-COP1), heritably modifies the expression pattern and cop1-like cosuppression phenotypes of multiple GFP-COP1 target loci by transcriptional gene silencing.ResultsHere we describe three additional features of trans-silencing by the C73 locus. First, the silencing phenotype of C73 and of similar complex loci was acquired epigenetically over the course of no more than two plant generations via a stage resembling posttranscriptional silencing. Second, imprints imposed by the C73 locus were maintained heritably for at least five generations in the absence of the silencer with only sporadic spontaneous reversion. Third, the pairing of two other GFP-COP1 transgene loci, L91 and E82, showed an increased tendency for epigenetic modification when L91 carried an epigenetic imprint from C73, but not when E82 bore the imprint.ConclusionsThe latter data suggest a transfer of trans-silencing activity from one transgene locus, C73, to another, namely L91. These results extend our operational understanding of interactions among transgenes in Arabidopsis.
Highlights
Heritable epimutations affecting transgene expression are not well understood, even and in particular in the plant model species, Arabidopsis thaliana
Unambiguous evidence for a cosuppression of transgene and endogene, as opposed to a dominant negative effect of the transgenic protein, has previously been shown for line L4 and others [27], and Constitutive Photomorphogenesis1 protein (COP1) endogene suppression was associated with green fluorescent protein (GFP)-COP1 silencing in T2 generation type C lines
Two additional oligomeric GFPCOP1 loci, C11 and C71, which have not been tested for their trans-silencing behavior, changed from a cosuppressing state in the T2 generation to a non-cosuppressing state in the T3 (Fig. 2A)
Summary
Heritable epimutations affecting transgene expression are not well understood, even and in particular in the plant model species, Arabidopsis thaliana. Certain genetic loci are known to modify the expression of other allelic or non-allelic partner loci in a meiotically heritable fashion. If allelic, such non-Mendelian interactions are referred to as paramutation. Interactions resembling paramutation occur among non-allelic transgene loci with DNA sequence homology. In these cases one master locus tends to suppress the expression of its target locus ('trans-silencing') [7,8,9,10,11]. Complex synthetic transgenes composed of PAI inverted repeats were able to trans-methylate homologous, yet non-allelic, target loci [12]. Similar events have been observed in other species [e.g. [13]]
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