Originally published as Genetics Published Articles Ahead of Print on December 18, 2006.

Genetics, Vol. 175, 1059-1070, March 2007, Copyright © 2007
doi:10.1534/genetics.106.066134

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

Rajandeep S. Sekhon^*, Thomas Peterson and Surinder Chopra^*,1

^* Department of Crop and Soil Sciences, Pennsylvania State University, University Park, Pennsylvania 16802 and Department of Genetics, Development and Cell Biology, Iowa State University, Ames, Iowa 50011

¹ Corresponding author: Department of Crop and Soil Sciences, 116 Agricultural Sciences and Industries Bldg., Pennsylvania State University, University Park, PA 16802.
E-mail: sic3{at}psu.edu

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

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Genetics 2007 175: NP. [Full Text]  

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