Mutator transposon insertion is associated with ectopic expression of a tandemly repeated multicopy Myb gene pericarp color1 of maize

• Published in: Genetics (Austin) Vol. 178; no. 4; pp. 1859 - 1874
• Main Authors: Robbins, M.L, Sekhon, R.S, Meeley, R, Chopra, S
• Format: Journal Article
• Language: English
• Published: United States Genetics Soc America 01.04.2008; Genetics Society of America
• Subjects: Alleles; chromatin; color; corn; Crosses, Genetic; Data collection; DNA Methylation; DNA Transposable Elements - genetics; Enhancer Elements, Genetic - genetics; Gene Dosage; Gene Expression Regulation, Plant; Genes, myb; Genes, Plant - genetics; Genetic Linkage; Genetics; Genotype & phenotype; Introns - genetics; Investigations; molecular sequence data; mutagenesis; Mutagenesis, Insertional; p1 gene; pericarp; pericarp color1 gene; pigmentation; Pigmentation - genetics; Plant Proteins - genetics; Plant Proteins - metabolism; Proteins; Quantitative Trait, Heritable; red pericarp; Sequence Analysis, DNA; Signal transduction; Tandem Repeat Sequences - genetics; transposition (genetics); transposons; Up-Regulation - genetics; Zea mays; Zea mays - genetics
• ISSN: 0016-6731; 1943-2631; 1943-2631
• DOI: 10.1534/genetics.107.082503

The molecular basis of tissue-specific pigmentation of maize carrying a tandemly repeated multicopy allele of pericarp color1 (p1) was examined using Mutator (Mu) transposon-mediated mutagenesis. The P1-wr allele conditions a white or colorless pericarp and a red cob glumes phenotype. However, a Mu-insertion allele, designated as P1-wr-mum6, displayed an altered phenotype that was first noted as occasional red stripes on pericarp tissue. This gain-of-pericarp-pigmentation phenotype was heritable, yielding families that displayed variable penetrance and expressivity. In one fully penetrant family, deep red pericarp pigmentation was observed. Several reports on Mu suppressible alleles have shown that Mu transposons can affect gene expression by mechanisms that depend on transposase activity. Conversely, the P1-wr-mum6 phenotype is not affected by transposase activity. The increased pigmentation was associated with elevated mRNA expression of P1-wr-mum6 copy (or copies) that was uninterrupted by the transposons. Genomic bisulfite sequencing analysis showed that the elevated expression was associated with hypomethylation of a floral-specific enhancer that is approximately 4.7 kb upstream of the Mu1 insertion site and may be proximal to an adjacent repeated copy. We propose that the Mu1 insertion interferes with the DNA methylation and related chromatin packaging of P1-wr, thereby inducing expression from gene copy (or copies) that is otherwise suppressed.