The Maize Unstable factor for orange1 Is a Dominant Epigenetic Modifier of a Tissue Specifically Silent Allele of pericarp color1

Abstract

<p>We have characterized <em>Unstable factor for orange1</em> (<em>Ufo1</em>), a dominant, allele-specific modifier of expression of the maize <em>pericarp color1</em> (<em>p1</em>) gene. The <em>p1</em> gene encodes an <em>Myb</em>-homologous transcriptional activator of genes required for biosynthesis of red phlobaphene pigments. The <em>P1-wr</em> allele specifies colorless kernel pericarp and red cobs, whereas <em>Ufo1</em> modifies <em>P1-wr</em> expression to confer pigmentation in kernel pericarp, as well as vegetative tissues, which normally do not accumulate significant amounts of phlobaphene pigments. In the presence of <em>Ufo1, P1-wr</em> transcript levels and transcription rate are increased in kernel pericarp. The <em>P1-wr</em> allele contains approximately six <em>p1</em> gene copies present in a hypermethylated and multicopy tandem array. In <em>P1-wr Ufo1</em> plants, methylation of <em>P1-wr</em> DNA sequences is reduced, whereas the methylation state of other repetitive genomic sequences was not detectably affected. The phenotypes produced by the interaction of <em>P1-wr</em> and <em>Ufo1</em> are unstable, exhibiting somatic mosaicism and variable penetrance. Moreover, the changes in <em>P1-wr</em> expression and methylation are not heritable: meiotic segregants that lack <em>Ufo1</em> revert to the normal <em>P1-wr</em> expression and methylation patterns. These results demonstrate the existence of a class of modifiers of gene expression whose effects are associated with transient changes in DNA methylation of specific loci.</p>