Linker histone H1 regulates immunity and defense priming in plants

Chromatin changes and nucleosome dynamics drive the fine tuning of gene expression in stress conditions. Besides core nucleosomal histones, linker histone H1 regulates gene expression by regulating RNA polymerase II accessibility to chromatin and epigenetic landscape, notably DNA methylation and histone H3 methylation/acetylation. The role of H1 in cell cycle regulation and disease progression is evident in animal systems, however we lack an understanding of their role in plant immunity. Here, we screened Arabidopsis mutants of three canonical variants of H1 namely H1.1, H1.2 and H1.3 for their disease progression and observed that double h1.1h1.2 and triple h1.1h1.2h1.3 (3h1) mutants were resistant to Pseudomonas syringae and Botrytis cinerea infections. Global transcriptome analysis revealed that the 3h1 mutant differentially regulates key defense related genes and has elevated levels of innate immunity. Interestingly, PAMP-induced defense priming was compromised in 3h1 and correlated with enhanced DNA methylation and reduced H3K56ac levels. These results reveal the molecular mechanism of H1 regulation in disease resistance and immunity in plants.