Epigenetic Modifications of Distinct Sequences of the p1 Regulatory Gene Specify Tissue-Specific Expression Patterns in Maize

摘要

Tandemly repeated endogenous genes are common in plants, but their transcriptional regulation is notnwell characterized. In maize, the P1-wr allele of pericarp color1 is composed of multiple copies arranged in anhead-to-tail fashion. P1-wr confers a white kernel pericarp and red cob glume pigment phenotype that isnstably inherited over generations. To understand the molecular mechanisms that regulate tissue-specificnexpression of P1-wr, we have characterized P1-wr*, a spontaneous loss-of-function epimutation that shows anwhite kernel pericarp and white cob glume phenotype. As compared to its progenitor P1-wr, the P1-wr* isnhypermethylated in exon 1 and intron 2 regions. In the presence of the epigenetic modifier Ufo1 (Unstablenfactor for orange1), P1-wr* plants exhibit a range of cob glume pigmentation whereas pericarps remainncolorless. In these plants, the level of cob pigmentation directly correlates with the degree of DNA demethylationnin the intron 2 region of p1. Further, genomic bisulfite sequencing indicates that a 168-bp regionnof intron 2 is significantly hypomethylated in both CG and CNG context in P1-wr* Ufo1 plants.nInterestingly, P1-wr* Ufo1 plants did not show any methylation change in a distal enhancer region that hasnpreviously been implicated in Ufo1-induced gain of pericarp pigmentation of the P1-wr allele. These resultsnsuggest that distinct regulatory sequences in the P1-wr promoter and intron 2 regions can undergonindependent epigenetic modifications to generate tissue-specific expression patterns.