Position: Post-doctoral Research Associate
Hometown: Harare, Zimbabwe
Education: Ph.D (2009), Plant Molecular and Cellular Biology Program (PMCB), University of Florida, Gainesville, FL.
B.S. (2004), Fort Valley State University, Fort Valley, GA.
Epigenetic regulation involves heritable modifications to chromatin that does not involve changes in DNA sequence. Such modifications include DNA (cytosine) methylation, histone modifications and changes in nucleosome distribution and overall chromatin compaction. Epigenetic modifications affect overall chromatin structure, accessibility of chromatin to regulatory proteins and gene expression. In plants, epigenetic modifications at gene promoters, repetitive sequences, transposons and transgenes can be associated with transcriptional gene silencing (TGS) via the RNA-dependent DNA methylation (RdDM) pathway. This pathway requires the production and activity of siRNAs to mediate epigenetic changes to chromatin at target loci (reviewed by Matzke et al. 2009). Several components of this pathway have been identified in maize and interestingly, many of these proteins also participate in paramutation (reviewed by Arteaga-Vazquez and Chandler, 2010). Using a forward genetic screen, we have identified additional novel epigenetic regulators of a transcriptionally silenced transgene in maize - the b1 genomic transgene (BTG-s), designated the transgene reactivated mutants (tgr). In these mutants, changes in promoter DNA methylation are associated with transgene activity (Madzima et al. 2011).
My work in the McGinnis Lab focuses on understanding the mechanisms global and local changes in chromatin structure in maize in response to a known epigenetic regulator: Mop1. The Mop1 gene encodes a putative RNA-dependent RNA polymerase (Alleman et al. 2006) required for several examples of epigenetic regulation of endogenous genes and transgenes in maize (Dorweiler et al. 2000; Lisch et al. 2002; McGinnis et al. 2006, Woodhouse et al. 2006) via the RdDM pathway. Based on mutant phenotypes, Mop1 likely influences chromatin structure on a genome-wide scale. We use Nimblegen microarray-based assays to characterize chromatin responses in maize. My research focuses on characterizing genomic response in chromatin accessibility in response to the mop1-1 mutation.
In maize, many components of the RdDM pathway are also involved in paramutation. Paramutation is allelic interaction in trans that results in heritable changes in expression of one allele (reviewed by Chandler 2010). I am also interested in understanding the mechanisms of paramutation and transgene silencing by components of the RdDM pathway such as Mop1.