title: Paramutagenicity of a p1 epiallele in maize.
abstract: Complex silencing mechanisms in plants and other kingdoms target transposons, repeat sequences, invasive viral nucleic acids and transgenes, but also endogenous genes and genes involved in paramutation. Paramutation occurs in a heterozygote when a transcriptionally active allele heritably adopts the epigenetic state of a transcriptionally and/or post-transcriptionally repressed allele. P1-rr and its silenced epiallele P1-pr, which encode a Myb-like transcription factor mediating pigmentation in floral organs of Zea mays, differ in their cytosine methylation pattern and chromatin structure at a complex enhancer site. Here, we tested whether P1-pr is able to heritably silence its transcriptionally active P1-rr allele in a heterozygote and whether DNA methylation is associated with the establishment and maintenance of P1-rr silencing. We found that P1-pr participates in paramutation as the repressing allele and P1-rr as the sensitive allele. Silencing of P1-rr is highly variable compared to the inducing P1-pr resulting in a wide range of gene expression. Whereas cytosine methylation at P1-rr is negatively correlated with transcription and pigment levels after segregation of P1-pr, methylation lags behind the establishment of the repressed p1 gene expression. We propose a model in which P1-pr paramutation is triggered by changing epigenetic states of transposons immediately adjacent to a P1-rr enhancer sequence. Considering the vast amount of transposable elements in the maize genome close to regulatory elements of genes, numerous loci could undergo paramutation-induced allele silencing, which could also have a significant impact on breeding agronomically important traits.
authors.affiliation: Waksman Institute of Microbiology, Rutgers University, 190 Frelinghuysen Road, Piscataway, NJ 08854, USA.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Goettel
authors.forename: Joachim
authors.initials: J
authors.lastname: Messing
mesh_terms: D000483:Alleles; D018899:CpG Islands; D003433:Crosses, Genetic; D003596:Cytosine / Q000378:metabolism; D019175:DNA Methylation; D044127:Epigenesis, Genetic; D020868:Gene Silencing; D017343:Genes, Plant; D005838:Genotype; D006579:Heterozygote; D008957:Models, Genetic; D009153:Mutagens; D009154:Mutation; D010641:Phenotype; D010858:Pigmentation; D010940:Plant Proteins / Q000235:genetics; D014158:Transcription, Genetic; D003313:Zea mays / Q000235:genetics*
chemical_list: D009153:Mutagens; D010940:Plant Proteins; D003596:Cytosine