Transgene-induced silencing identifies sequences involved in the establishment of paramutation of the maize p1 gene.
A transgene carrying a distal enhancer element of the maize P1-rr promoter caused silencing of an endogenous P1-rr allele in the progeny of transgenic maize plants. Expression of both the transgene and the endogenous P1-rr allele was reduced in the affected plants. The silenced phenotype was observed in the progeny of seven of eight crosses involving three independent transgenic events tested (average frequency of 19%). This phenotype was associated with an induced epigenetic state of the P1-rr allele, termed P1-rr', which is characterized by increased methylation of the P1-rr flanking regions and decreased levels of P1-rr transcript. The P1-rr' epiallele is highly heritable in the absence of the inducing P1.2b::GUS transgene, and it can impose an equivalent state on a naive P1-rr allele in subsequent crosses (paramutation). In contrast, parallel experiments with two other P::GUS transgenes that contained the same basal P1-rr promoter fragment but different upstream sequences revealed no detectable silencing effect. Thus, transgenes carrying a specific enhancer fragment of the P1-rr gene promoter can trigger a paramutant state (P1-rr') of the endogenous P1-rr gene that is maintained in the absence of the inducing transgene. We discuss the potential role of the P1-rr distal enhancer element in the establishment and propagation of a paramutation system in maize.
Department of Zoology and Genetics, Iowa State University, Ames, Iowa 50011, USA.
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Sidorenko
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Peterson
D000483:Alleles; D003433:Crosses, Genetic; D019175:DNA Methylation; D018744:DNA, Plant / Q000737:chemistry / Q000235:genetics; D004742:Enhancer Elements, Genetic; D020868:Gene Silencing; D017343:Genes, Plant; D008957:Models, Genetic; D009154:Mutation; D010641:Phenotype; D030821:Plants, Genetically Modified; D011401:Promoter Regions, Genetic; D020080:Tandem Repeat Sequences; D014158:Transcription, Genetic; D003313:Zea mays / Q000235:genetics*
D018744:DNA, Plant