Linker histone H1 modulates defense priming and immunity in plants

Abstract

Linker H1 histones play an important role in animal and human pathogenesis, but their function in plant immunity is poorly understood. Here, we analyzed mutants of the three canonical variants of Arabidopsis H1 histones, namely H1.1, H1.2 and H1.3. We observed that double h1.1h1.2 and triple h1.1h1.2h1.3 (3h1) mutants were resistant to Pseudomonas syringae and Botrytis cinerea infections. Transcriptome analysis of 3h1 mutant plants showed H1s play a key role in regulating the expression of early and late defense genes upon pathogen challenge. Moreover, 3h1 mutant plants showed enhanced production of reactive oxygen species and activation of mitogen activated protein kinases upon pathogen-associated molecular pattern (PAMP) treatment. However, 3h1 mutant plants were insensitive to priming with flg22, a well-known bacterial PAMP which induces enhanced resistance in WT plants. The defective defense response in 3h1 upon priming was correlated with altered DNA methylation and reduced global H3K56ac levels. Our data place H1 as a molecular gatekeeper in governing dynamic changes in the chromatin landscape of defense genes during plant pathogen interaction.

Finding a good balance: two distinct chromatin factors fine‐tune stress response in Arabidopsis seedlings

“…In the recent report by Sheikh et al . (2023), changes in H3K56ac levels were correlated with the role of Arabidopsis H1 in the regulation of the defense gene expression after pathogen challenge. However, H3K27me3 levels were not significantly altered in the 3h1 mutant under these conditions.…”

“…Additionally, it will be important to determine whether H1 binding changes under stress conditions and whether it depends on H3K9/14 (de)acetylation and the presence of HDC1. Intriguingly, in both animals and plants, H1s have been functionally linked with a different histone acetylation mark, H3K56ac (Bernier et al ., 2015; Sheikh et al ., 2023). Therefore, it would be interesting to test whether HDC1 mediates deacetylation of this and/or other sites, or even H1, under salt stress.…”

Editorial: Systemic resistance and defense priming against pathogens

“…The establishment and maintenance of defense priming involve various processes, including epigenetic alterations, accumulation of inactive signaling factors, and changes in the levels of immune receptors, e.g. , pattern-recognition receptors ( Beckers et al., 2009 ; Tateda et al., 2014 ; Cecchini et al., 2015 ; Conrath et al., 2015 ; Tsuda and Somssich, 2015 ; Baum et al., 2019 ; Jiang et al., 2021 ; Sheikh et al., 2023 ). Different systemic resistance programs are activated depending on the specific stimulus in different plant organs/tissues and the long-distance mobile signals implicated ( De Kesel et al., 2021 ).…”