The Arabidopsis RRM domain protein EDM3 mediates race-specific disease resistance by controlling H3K9me2-dependent alternative polyadenylation of RPP7 immune receptor transcripts.

The NLR-receptor RPP7 mediates race-specific immunity in Arabidopsis. Previous screens for enhanced downy mildew (edm) mutants identified the co-chaperone SGT1b (EDM1) and the PHD-finger protein EDM2 as critical regulators of RPP7. Here, we describe a third edm mutant compromised in RPP7 immunity, edm3. EDM3 encodes a nuclear-localized protein featuring an RNA-recognition motif. Like EDM2, EDM3 promotes histone H3 lysine 9 dimethylation (H3K9me2) at RPP7. Global profiling of H3K9me2 showed EDM3 to affect this silencing mark at a large set of loci. Importantly, both EDM3 and EDM2 co-associate in vivo with H3K9me2-marked chromatin and transcripts at a critical proximal polyadenylation site of RPP7, where they suppress proximal transcript polyadeylation/termination. Our results highlight the complexity of plant NLR gene regulation, and establish a functional and physical link between a histone mark and NLR-transcript processing.