The Arabidopsis Chromatin Remodeling Factor CHR5 Regulates Plant Immune Responses and Nucleosome Occupancy.

ATP-dependent chromatin remodeling factors use the energy of ATP hydrolysis to alter the structure of chromatin and are important regulators of eukaryotic gene expression. One such factor CHR5 (Chromatin Remodeling Factor 5) in Arabidopsis (Arabidopsis thaliana) was previously found to be involved in growth and development regulation. Here we show that CHR5 is required for the upregulation of the intracellular immune receptor gene SNC1 (SUPPRESSOR OF npr1-1, CONSTITUTIVE1) and consequently the autoimmunity induced by SNC1 upregulation. CHR5 functions antagonistically with another chromatin remodeling gene DDM1 (DECREASED DNA METHYLATION 1) and independently with a histone mono-ubiquitinase HUB1 (HISTONE MONOUBIQUITINATION 1) in SNC1 regulation. In addition, CHR5 is a positive regulator of SNC1-independent plant immunity against bacterial pathogens Pseudomonas syringae. Furthermore, the chr5 mutant has increased nucleosome occupancy in the promoter region relative to the gene body region at the whole genome level, suggesting a global role of CHR5 in remodeling nucleosome occupancy. Our study thus establishes CHR5 as a positive regulator of plant immune responses including the expression of SNC1 and reveals a role of CHR5 in nucleosome occupancy which likely impact gene expression genome-wide.

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