The N-Terminal Tail of H2A.Z Modulates the Magnitude of Transcriptional Response to Abscisic Acid in Arabidopsis thaliana

ABSTRACT: The role of the highly histone variant H2A.Z remains engimatic, in part because of its context-dependent effects on modulating transcription. Here, we investigate the role of the H2A.Z N-terminal tail in regulating transcriptional responses to the stress hormone abscisic acid (ABA) in Arabidopsis thaliana. In WT plants, treatment with ABA induces hundreds of transcripts to be rapidly up- and downregulated. Using h2a.z null mutant plants expressing either an H2A.Z missing the entire N-temrinal tail (Delta28), or carrying lysine to arginine mutations in either a single lysine (K>R 3) or all nine N-terminal lysines (K>R 1-9), we find that the H2A.Z N-terminus is surprisingly dispensable for the intiation of the ABA response program, but plays an important role in fine-tuning the magnitude of response. Interestingly, distinct subsets of genes exhibit altered response magnitude in each mutant, with limited overlap between genotypes. The most significantly dysregulated of these in the mutants compared to WT are associated with chromatin context: genes upregulated by ABA are enriched for gene-body H2A.Z (gbH2A.Z) at baseline, and show increased expression in mutants primarily under mock (non-ABA) conditions. Meanwhile, ABA-repressed genes tend to be enriched for transcription start site (TSS)-localized H2A.Z at baseline, and exhibit enhanced repression in mutants upon ABA treatment. Notably, the K>R 1-9 mutant produces more differentially expressed genes (DEGs) compared to WT in both mock and ABA-treated conditions that does complete removal of the tail, indiciating that loss of modifiability is not equivalent to loss of the N-terminus. Together, our results support a model in which the major regulatory functions of H2A.Z reside in the highly conserved histone fold domain, while the more evolutionarily variable N-terminal tail acts as a bidirectional buffer to fine-tune transcirptional output. While dispensable for the broad execution of transcriptional programs, this fine-tuning capacity is critical for maintaining transcriptional precision during stress responses, with implications for organismal fitness.

ORGANISM(S): Arabidopsis thaliana

PROVIDER: GSE338700 | GEO | 2026/07/24

REPOSITORIES: GEO