Graduate Student Emory University Decatur, Georgia
Body of Abstract: In the plant nucleus, histone proteins bind and package DNA into chromatin. Histones and trans-acting factors are in a constant battle over DNA access; histones must bind to package DNA, and trans-acting factors must access DNA sequence to coordinate gene expression specific to a plants’ developmental and environmental state. Modulation of DNA-histone interactions is therefore crucial to promote proper gene expression at any given moment within the cell. In the model plant organism Arabidopsis thaliana, the chromatin remodeler SWI2/SNF2-Related 1 (SWR1) regulates DNA-histone interactions by depositing the conserved histone variant H2A.Z. H2A.Z is a highly conserved, divergent histone essential for plant environmental response and phase transitions. H2A.Z is deposited at a wide range of sites throughout the Arabidopsis genome and is associated with a myriad of processes anywhere from transcriptional regulation to DNA repair. The unifying mechanism behind how H2A.Z is deposited to participate in such diverse functions is unknown. We previously found that H2A.Z deposition in Arabidopsis is dependent on the protein Methyl-cpg-Binding Domain-containing protein 9 (MBD9). MBD9 complexes with SWR1, but the mechanism behind MBD9-mediated H2A.Z deposition is not well defined. To address this, we altered two putative domains of MBD9 and investigated the downstream effects of these alterations on SWR1 recruitment and H2A.Z deposition using enhanced Chromatin ImmunoPrecipitation followed by Sequencing (eChIP-Seq). We found that a functional MBD9 acetyl-binding Bromo domain is not necessary for proper H2A.Z deposition and that the substitution of another domain results in the mis-localization of MBD9 to new sites where SWR1 and H2A.Z follow. Interestingly, we also see that SWR1 and MBD9 do not associate with facultative heterochromatin, indicating that SWR1 targeting could be linked to transcription. Taken together, these results help us clarify the role of SWR1 and H2A.Z in the regulation of DNA-histone interactions.