Multiple chromatin-associated modules regulate expression of an intracellular immune receptor gene in Arabidopsis

The expression of an intracellular immune receptor gene SNC1 (SUPPRESSOR OF npr1, CONSTITUTIVE 1) is regulated by multiple chromatin-associated proteins for tuning immunity and growth in Arabidopsis. Whether and how these regulators coordinate to regulate SNC1 expression under varying environmental conditions is not clear. Here, we identified two activation and one repression regulatory modules based on genetic and molecular characterizations of five chromatin-associated regulators of SNC1. Modifier of snc1 (MOS1) constitutes the first module and is required for the interdependent functions of ARABIDOPSIS TRITHORAX-RELATED 7 (ATXR7) and HISTONE MONOUBIQUITINATION 1 (HUB1) to deposit H3K4me3 and H2Bub1 at the SNC1 locus. CHROMATIN REMODELING 5 (CHR5) constitutes a second module and works independently of ATXR7 and HUB1 in the MOS1 module. HIGH EXPRESSION OF OSMOTICALLY RESPONSIVE GENES 15 (HOS15) constitutes a third module responsible for removing H3K9ac to repress SNC1 expression under nonpathogenic conditions. The upregulation of SNC1 resulting from removing the HOS15 repression module is partially dependent on the function of the CHR5 module and the MOS1 module. Together, this study reveals both the distinct and interdependent regulatory mechanisms at the chromatin level for SNC1 expression regulation and highlights the intricacy of regulatory mechanisms of NLR expression under different environment.