Poster: Chromatin Remodeling & Epigenetics

Abs # 1025: Epigenetic mechanisms and chromatin modifications controlling nucleolar dominance

Presenter:	Pikaard, Craig S, pikaard@biology.wustl.edu
Authors	Pikaard, Craig S (A)   Lawrence, Richard  (A)   Lewis, Michelle  (A)   Pikaard, Diane  (A)   Preuss, Sasha  (A)   Brower-Toland, Brent  (A)
Affiliations:	(A): Biology Department, Washington University, St. Louis, MO; USA
Web Site:	http://www.biology.wustl.edu/pikaard/

The silencing of one parent's ribosomal RNA genes in an inter-species hybrid is the epigenetic phenomenon known as nucleolar dominance. In Arabidopsis suecica, the allotetraploid hybrid of A. thaliana and A. arenosa, and in diploid A. thaliana x A. lyrata hybrids, the rRNA genes derived from A. thaliana are selectively silenced. Using RNA interference (RNAi) technology, we are systematically knocking down the expression of chromatin modifying enzymes and determining the consequences for nucleolar dominance. Targeting 13 genes representing the four families of histone deacetylases (HDAs) has revealed one HDA, within the family related to yeast Rpd3, that is required for rRNA gene silencing in nucleolar dominance. We have devised methods for obtaining pure nucleosomal histones and have identified all the core histones, including variants, using mass spectrometry. We have also identified the amino-terminal lysines of histones H3 and H4 that are acetylated and are determining the substrate specificity of the HDA that enforces nucleolar dominance. Interestingly, knocking down a variety of chromatin modifying activities, including HDAs, has little phenotypic consequence in A. thaliana but causes dramatic developmental abnormalities in hybrids, suggesting that epigenetic mechanisms are key to hybrid vigor.