Functional dissection of the VIM1 protein and its role in cytosine methylation in Arabidopsis
Elena Cravens, Molly Shook, Eric Richards
Epigenetics is the study of chromatin modifications, such as cytosine methylation and histone modification, which affect gene expression. VARIANT IN METHYLATION 1 (VIM1) is an epigenetic regulator required for both maintenance of DNA methylation and centromeric heterochromatin compaction in Arabidopsis thaliana. The VIM1 protein has a methyl DNA binding SRA (SET- and RING-associated) domain, as well as a PHD (plant homeo-domain) and two RING (presumptive ubiquitin E3 ligase) domains. We hypothesized that the VIM1 protein SRA domain is involved in maintaining cytosine methylation in Arabidopsis but that the RING and PHD domains are dispensable. To test this hypothesis, PHD and RING point mutants were expressed in vim1 null mutants. We studied whether or not the centromeric repeats were fully methylated in transgenic plants expressing the mutated versions of VIM1 using DNA blots of genomic DNA digested with methylation-sensitive endonucleases. Contrary to our original hypothesis, we found that the centromeric repeats portion of the DNA was not methylated in the plant lines expressing VIM1 containing point mutations in each domain, suggesting that both the PHD and RING domains in the VIM1 protein are involved in the maintenance of cytosine methylation. We are now investigating the role of VIM1, and the PHD and RING domains, in both centromere condensation and methylation. Our research can lead to new knowledge about how epigenetic modifications occur in plants as well as humans.