Role of the Histone Variant Protein H2A.Z in H3K27me3 Homeostasis in Arabidopsis Thaliana

The histone variant protein H2A.Z plays a conserved role in transcription, replication, and repair in eukaryotic organisms. In plant chromatin, H2A.Z is enriched in the body of genes that are associated with differentiation and environmental responsivity and is generally thought to contribute to responsive gene expression in plants. H2A.Z is also enriched in the body of genes that are enriched for the repressive histone modification H3K27me3 in Arabidopsis. H3K27me3 is necessary for proper plant growth and development, and its loss is associated with failed differentiation and callus formation. Previous work from the lab has suggested that the presence of H2A.Z can enable deposition of H3K27me3. In particular, loss of PIE1, a conserved ATP-dependent chromatin remodeler that promotes deposition of H2A.Z in all eukaryotes, results in reduced levels of both the histone variant H2A.Z and of the histone modification H3K27me3. Although these data raise the possibility that SWR1 promotes H3K27me3 in an H2A.Z-dependent fashion, it is also possible that SWR1 acts via an independent mechanism. There are three genes that codes for H2A.Z in Arabidopsis: HTA8, HTA9, and HTA11. To test the hypothesis that loss of H2A.Z is sufficient to alter H3K27me3 levels, we are using RNA-seq and ChIP-seq to examine gene expression and chromatin-associated features in wild-type (WT) and hta9 hta11 plants. We complemented these genome-wide analysis with examination of environmentally responsive gene expression of genes enriched for H2A.Z. In addition, we are examining H2A.Z-dependent environmentally responsive traits such as hypocotyl elongation in response to heat stress. The analysis of the associated data is ongoing and will help to clarify the role of H2A.Z in homeostasis of H3K27me3 and in gene expression. This research has been funded by the National Science Foundation and the American Society of Plant Biology.