Genetic Control of Anthocyanin Biosynthesis in Maize
We are investigating the control of gene expression in different cell types and at different developmental stages by studying the regulated expression of the genes required for anthocyanin biosynthesis in maize. More than thirty naturally occurring alleles of the regulatory gene b have been described that show differences in the timing and tissue distribution of pigment synthesis. In higher plants, this system provides one of only a few examples of a known regulatory protein, which coordinately regulates a number of target genes that are cloned and characterized. Certain b alleles also undergo paramutation -- a heritable alteration in gene expression promoted by the presence of two specific alleles in the same plant. Our long-term goals are to understand how the B protein coordinately regulates the pathway in a tissue and developmental-specific manner and to determine the molecular mechanisms of b
paramutation.
Our recent experiments have demonstrated that differential anthocyanin synthesis conferred by various b alleles correlates with tissue-specific b mRNA accumulation. Cloning and DNA sequence analyses demonstrate that two b alleles with differential patterns of expression are 98 percent identical in the coding region but are completely divergent in a region of the leader mRNA and promoter sequences. In vitro mutagenesis and transformation experiments are in progress to identify the sites required for differential expression of these alleles. Experiments are also in progress to investigate the mechanism of B activation of the anthocyanin pathway. Recent experiments strongly suggest the B protein plays a major role in stimulating structural gene transcription. We are using both in vitro and in vivo assays to identify the regions of the B protein necessary for regulation, determine the function of these regions, and identify and investigate other proteins interacting with the B protein.
Paramutation at b occurs when a dark purple plant containing the B-I allele is heritably changed to B' (light purple phenotype) when B-I and B' are together in an
heterozygote. Paramutation could reflect directed, meiotically heritable changes in chromatin structure or DNA modification, directed DNA rearrangements, or gene conversion. We are examining the various alleles for structural differences using DNA blot analyses and cloning, analyzing b expression to determine the basis for altered pigment accumulation, developing functional assays using particle gun transformation, and isolating mutations with altered paramutation properties.
|
Search: [ current | former scholar ] [ current | awarded institution ] [ quick search ]
