Pikaard studies what's known as transcriptional gene silencing. This phenomenon is often regulated by short interfering RNAs, or siRNAs, which University of Cambridge scientist David Baulcombe has called "the dark matter of genetics". By bringing about changes in DNA that interfere with transcription -- the copying of DNA to RNA -- siRNAs can effectively extinguish gene expression at its earliest stage. Pikaard explains, "From yeast to plants to humans these small RNAs can specify the modification of DNA somehow in a way that prevents transcription in the first place." According to Pikaard, most eukaryotes use the same two-pronged method for silencing genes at the transcriptional level: DNA methylation, or adding chemical flags to genes, and modification of proteins called histones that act as spools for DNA.
All eukaryotes share three essential RNA polymerases: Pol I, II, and III. These polymerases are indispensable for expressing biological traits and play a critical role in maintaining basic metabolic functions necessary for survival. "If you're mutated for any of those, you die," says Pikaard. "However, Pol IV and Pol V -- which only plants have -- you don't need them to stay alive but they turn out to be really important for this whole RNA-directed silencing phenomenon."
Since discovering these plant-specific RNA polymerases a few years ago, Pikaard's lab has been on a hunt to figure out what Pol IV and Pol V are making. In 2005, Pikaard and his collaborators published research showing that the major function of Pol IV is to generate siRNAs, thereby singling out this RNA polymerase as a potential player in gene silencing. However, when subsequent genetic tests suggested that Pol V is also needed for gene silencing, but not siRNA production, Pikaard and his colleagues suspected that Pol V and Pol IV cooperate, but work independen
|Contact: Craig Pikaard|
Washington University in St. Louis