A new layer of chromatin regulation in plant salt tolerance: <scp>H3K37ac</scp> emerges as an evolutionarily conserved stress‐responsive histone mark

Given its location in the nucleosome core, H3K37ac may alter DNA unwrapping kinetics, facilitate chromatin remodeler recruitment, or enhance transcription factor access… Histone acetylation has been extensively studied at canonical N-terminal lysines, such as H3K9ac, H3K14ac, H3K27ac, and H4K5ac, which collectively loosen chromatin structure and promote transcription (Chen et al., 2024). Acetylation within the histone core domain is comparatively underexplored, though emerging evidence suggests that it may influence nucleosome stability, DNA accessibility, and transcription factor recruitment (Tropberger & Schneider, 2013). The discovery of H3K37ac is therefore notable. Lysine 37 resides near the DNA entry/exit site of the nucleosome, a region critical for regulating DNA ‘breathing’ dynamics. The evolutionary conservation of this residue from budding yeast to mammals and across plant species indicates that its acetylation could represent a widespread regulatory mechanism. Ma et al. convincingly validate the existence of H3K37ac using mass spectrometry, peptide competition assays, and genetic mutagenesis – an essential step given the challenges in distinguishing low-abundance or recently evolved histone marks. A key discovery of the study is that salt stress triggers a genome-wide increase in H3K37ac. While several acetylation marks respond to environmental cues (Yuan et al., 2013; Luo et al., 2017), the rapid and pronounced induction of H3K37ac stands out among tested conditions (heat, cold, osmotic stress). Genome-wide CUT&Tag mapping reveals that, under salinity, thousands of genes gain H3K37ac enrichment, particularly near transcription start sites and gene bodies. This aligns H3K37ac with other active acetyl marks known to facilitate transcription (Liu et al., 2014). Importantly, genes gaining H3K37ac during salt stress include master regulators of osmotic and ionic homeostasis, such as HsfC1b, CBL1, CIPK24/SOS2, PRX29, and PRX61, canonical components of the salt stress regulatory network (Deinlein et al., 2014). Such coordinated changes support the idea that H3K37ac functions as an active epigenetic signal enabling rapid transcriptional reprogramming during environmental stress. Histone acetylation dynamics are governed by the opposing actions of histone acetyltransferases (HATs) and histone deacetylases (HDACs). Multiple studies have established HDACs as critical regulators of abiotic stress adaptation (Luo et al., 2017). In Arabidopsis, HDA9 represses drought and salt responses (Zheng et al., 2016), whereas HDA6 and HD2C positively regulate salt responses (Sridha & Wu, 2006; Chen et al., 2010; Luo et al., 2012b). In rice, HDA706 enhances salt tolerance by deacetylating H4K5/K8ac (Liu et al., 2023). In this context, the identification of HDA705 as a deacetylase that specifically removes H3K37ac is a major advance. Loss-of-function hda705 mutants show elevated H3K37ac and enhanced transcription of stress-responsive genes, alongside striking improvements in salt survival. These findings position HDA705 as a chromatin ‘brake’ on salt tolerance, a discovery that could translate into practical breeding or biotechnological applications. An important future step will be clarifying whether HDA705 acts exclusively on H3K37ac or also modulates a broader substrate spectrum. Previous work suggests HATs and HDACs often have multiple histone and nonhistone targets (Shih et al., 2025), raising the possibility of coordinated multimark regulation during stress. Over the last decade, the plant chromatin field has greatly expanded the known diversity of histone modifications. Novel marks, including H3K56ac, H3K122ac, and diverse histone acylations have revealed unexpected layers of chromatin regulation (Yang et al., 2020). The discovery of H3K37ac adds to this growing repertoire and underscores the continuing need for systematic, unbiased proteomic discovery. Mechanistically, H3K37ac is uniquely positioned to influence nucleosome architecture. Given its location in the nucleosome core, H3K37ac may alter DNA unwrapping kinetics, facilitate chromatin remodeler recruitment, or enhance transcription factor access: mechanisms established for other core-domain acetylations (Tropberger & Schneider, 2013). Identifying ‘reader’ proteins that recognize H3K37ac will be crucial for defining its functional consequences. By uncovering H3K37ac, Ma et al. illuminate a previously unrecognized layer of chromatin regulation in plant stress biology. Their work raises several exciting questions. Which/what acetyltransferase(s) catalyze H3K37ac deposition? Do interacting proteins (‘readers’) interpret H3K37ac as a transcriptional activation signal? What structural or biophysical effects does H3K37ac impart on the nucleosome? Is this modification conserved and functional across diverse crops? Addressing these questions will deepen our understanding of how chromatin encodes environmental responses and offers promising routes to strengthen crop resilience in an increasingly stressful world. This work was supported by the National Science and Technology Council of Taiwan (114-2311-B-002-019) and National Taiwan University (15L891901 and 115L8516). The New Phytologist Foundation remains neutral with regard to jurisdictional claims in maps and in any institutional affiliations.