Proceedings of the National Academy of Sciences of the United States of America

About the PNAS Member Editor
Name Pikaard, Craig S.
Location Indiana University
Primary Field Plant, Soil and Microbial Sciences
Secondary Field Plant Biology
 Election Citation
Pikaard has revealed fundamental epigenetic mechanisms of gene dosage control and gene silencing in plants. He is a pioneer in studies of ribosomal RNA locus control, and has studied the specialized RNA polymerases Pol IV and Pol V that direct site-specific DNA methylation and formation of repressive chromatin.
 Research Interests
Craig Pikaard's laboratory is interested in how specific genes are targeted for silencing. One focus is the selective silencing of ribosomal RNA (rRNA) genes, which are genes encoding RNAs needed for the assembly and function of ribosomes, the protein-synthesizing machines of cells. Eukaryotes have hundreds of rRNA genes that are nearly identical in sequence. During early development, virtually all rRNA genes are active. However, later in development, only a subset of rRNA is active. Pikaard's lab has shown that the non-expressed genes are inactivated by DNA methylation and repressive histone modifications, with the choice of which genes to silence somehow dictated by the chromosomal positions of the genes, and not their sequences. Studies to understand the molecular basis for the choice mechanism are ongoing. A second focus of the lab is to understand the roles of nuclear multisubunit RNA polymerases IV and V in RNA-directed DNA methylation (RdDM), a process needed to silence transposable elements as well as a subset of genes. Using a combination of biochemical assays conducted in vitro and genetic and genomic experiments in vivo, Pikaard's lab is working to understand how Pol IV and Pol V transcription is initiated, terminated and coupled with the activities of other enzymes in the RdDM pathway.

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