H3K27me3 Dynamic Turnover as a Gate Keeper of Defence Gene Expression in Arabidopsis

Background: Histone 3 lysine 27 tri-methylation (H3K27me3) is a chromatin mark typically associated with transcriptional repression. Histone demethylation, and particularly the removal of H3K27me3, has been linked to abiotic stress tolerance in plants. However, less is known about its role in biotic stress responses. Methods: We exploited immunity-related transcriptomics data combined with chromatin-state data to identify an association between chromatin modifications and plant immunity in Arabidopsis thaliana. We also measured the expression and H3K27me3 levels at immune-responsive loci, at Col-0 and at histone deacetylase mutants. Results: We identified H3K27me3 as a mark correlated with the silencing of defence gene loci. Moreover, we showed that the expression of a subset of flg22-induced genes is repressed by H3K27me3 prior to elicitation, and that expression negatively correlates with the mark upon activation of immunity. Notably, our studies also revealed a role for the H3K27 demethylase REF6 in plant defence. Loss of REF6 allows ectopic H3K27me3 deposition at target genes, revealing that these loci are actively regulated by the demethylase. Conclusions: Our data provide insight into the regulation of plant immune responses through chromatin dynamics.