RUI: Genetic and Epigenetic Mechanisms Generating r1 Gene Complexity in Maize

Duquesne University, Pittsburgh PA

Investigators

Abstract

The maize R gene (red-1) encodes a helix-loop-helix transcription factor that determines the timing and tissue-specificity of anthocyanin expression. Anthocyanin is a non-essential plant pigment that can be used as a marker for gene expression. The R locus exhibits epigenetic phenomena such as genomic imprinting and paramutation. Imprinting is apparent in the differential expression of aleurone depending upon parental inheritance of the gene. Paramutation is a form of epigenetic silencing in which the presence of a specific allele such as R-st affect the level of expression of a sensitive allele such as R-r. Both imprinting and paramutation are linked to structural properties of R haplotypes. These structural properties include 1) haplotype complexity or gene number, 2) gene structure, for example, the presence or absence of inverted repeats, 3) transposable element insertion, and 4) cytosine methylation. A molecular genetic approach will be applied to the problem of R gene complexity and expression. The specific aims are: 1. To characterize R haplotypes from races of maize. A phylogenetic tree will be constructed with these data. Tissue specificity of anthocyanin distribution will be surveyed and alleles will be characterized in terms of paramutagenicity, paramutability and imprinting. 2. To use genetic recombination to separate selected haplotypes into single transcriptional unit genes to compare the anthocyanin distribution for each gene. 3. To define the 5' flanking regions of each of the unique non-imprinting alleles and to determine the distribution of methyl-cytosine in the DNA. The results from this study will give more insight into the structural and evolutionary aspects of genes exhibiting epigenetic phenomena, such as the maize R family.